# Choosing the Right Diagnostic Test

## Quick Answer

- Select diagnostic tests by matching the clinical question to test type, considering sensitivity, specificity, cost, invasiveness, and turnaround time for each suspected condition.
- Start with the least invasive test that can confirm or exclude the leading differential, then escalate to more definitive sampling when initial results remain ambiguous.
- No single test provides perfect accuracy, and false negatives occur with early infections, prior vaccination, or sampling error, so interpret results alongside physical examination findings.

## At a Glance

The table below summarizes common diagnostic test categories and their practical applications in veterinary practice. This framework helps clinicians match the clinical question to the appropriate laboratory method.

| Test Category | Primary Clinical Question | Key Considerations | Typical Turnaround |
| --- | --- | --- | --- |
| Serology (antibody detection) | Has the animal been exposed to or vaccinated against a specific pathogen? | Cannot distinguish active infection from past exposure or vaccination, timing of sample collection affects results | 1 to 7 days depending on laboratory |
| PCR (nucleic acid detection) | Is the pathogen present in this sample right now? | High sensitivity for active infection, requires proper sample handling and timing, can detect nonviable organisms | 1 to 3 days for standard panels |
| Cytology | What cell types are present in a mass, fluid, or tissue sample? | Rapid, minimally invasive, provides preliminary classification of inflammation, infection, or neoplasia | Same day in most practice settings |
| Histopathology | What is the tissue architecture and definitive diagnosis? | Requires biopsy, provides definitive diagnosis for neoplasia and many inflammatory conditions | 3 to 7 days after submission |
| Culture and sensitivity | Which bacteria are present and which antibiotics will kill them? | Essential for chronic infections, treatment failures, and antimicrobial stewardship | 3 to 7 days for bacterial culture |

## The Clinical Decision Framework

Veterinary diagnostic test selection begins with a clear definition of the clinical question. The clinician must determine whether the goal is to confirm a suspected diagnosis, exclude a differential diagnosis, monitor disease progression, or guide therapeutic decisions. Each goal requires a different testing strategy, and the choice of test affects the interpretation of results.

The decision framework follows a logical sequence. First, establish the signalment, history, and physical examination findings. Second, rank the differential diagnoses by likelihood based on prevalence, exposure history, and clinical signs. Third, select the test that best discriminates between the leading differentials while considering the practical constraints of the patient, the owner, and the practice. Fourth, interpret the results in the context of the test characteristics and the clinical picture.

The Merck Veterinary Manual provides background on the clinical presentation of common diseases and the diagnostic approaches used in practice. This resource supports the clinician in understanding which tests are appropriate for specific conditions and how to interpret results in the context of the patient's history and physical findings.

### Matching Test to Clinical Question

The clinical question determines the test category. For example, when a veterinarian suspects an infectious disease, the choice between serology and PCR depends on whether the question is about exposure or active infection. Serology detects antibodies produced by the host in response to infection or vaccination, while PCR detects the genetic material of the pathogen itself.

For endocrine diseases such as hypothyroidism or hyperadrenocorticism, the question is about hormone levels and dynamic function. These conditions require specific hormone assays, often with stimulation or suppression testing to establish a diagnosis. The choice of test depends on the sensitivity and specificity of each assay for the suspected condition.

For neoplastic diseases, the question is about the nature of the mass and the degree of invasiveness. Cytology provides a preliminary assessment of cell types, while histopathology provides a definitive diagnosis based on tissue architecture. The choice between these tests depends on the accessibility of the lesion, the risk of sampling, and the need for a detailed explanation.

### Test Performance Characteristics

Sensitivity and specificity are the fundamental performance characteristics of any diagnostic test. Sensitivity is the probability that a test will be positive when the disease is present. Specificity is the probability that a test will be negative when the disease is absent. A test with high sensitivity is useful for excluding disease when negative, while a test with high specificity is useful for confirming disease when positive.

The positive and negative predictive values of a test depend on the prevalence of the disease in the population being tested. A test with high sensitivity and specificity may still produce false positives or false negatives when the disease prevalence is low. Clinicians must consider the pretest probability of disease when interpreting test results.

The World Organisation for Animal Health provides official guidance on animal health surveillance and reporting, which includes the use of diagnostic tests for disease detection and monitoring. This context is relevant for clinicians who work with livestock or who encounter reportable diseases in companion animals.

## Core Principles of Test Selection

The selection of a diagnostic test involves balancing several factors. The clinician must consider the accuracy of the test, the cost to the owner, the invasiveness of the sampling procedure, and the turnaround time for results. These factors are often in tension, and the clinician must prioritize based on the clinical situation.

### Accuracy and Reliability

The accuracy of a test is determined by its sensitivity and specificity, but also by the quality of the sample and the laboratory performing the test. Sample handling errors, such as improper storage or delayed transport, can affect the results of PCR and culture. The clinician must follow the laboratory's instructions for sample collection and transport to ensure reliable results.

The reliability of a test also depends on the stage of the disease. For example, serology may be negative in the early stages of infection before the host has produced detectable antibodies. PCR may be negative if the organism is not present in the sample collected, even if the animal is infected. The clinician must consider the timing of the test relative to the onset of clinical signs.

### Cost and Client Considerations

The cost of diagnostic testing is a significant factor in veterinary practice. The clinician must discuss the cost of each test with the owner and consider the owner's ability to pay. The American Veterinary Medical Association provides resources for pet owners about preventive care and the importance of regular veterinary visits, which can help owners understand the value of diagnostic testing.

The American Animal Hospital Association provides practice guidance for companion-animal care, including preventive care and life-stage considerations. These guidelines help clinicians structure their approach to diagnostic testing within the context of routine care.

### Invasiveness and Risk

The invasiveness of a diagnostic test ranges from noninvasive blood collection to surgical biopsy. The clinician must consider the risk of the procedure to the patient and the potential for complications. For example, a fine-needle aspirate of a superficial mass is minimally invasive and carries low risk, while a surgical biopsy of an internal organ requires anesthesia and carries higher risk.

The World Small Animal Veterinary Association provides global guidelines for companion-animal care, including vaccination and clinical guidelines. These guidelines help clinicians understand the appropriate use of diagnostic tests in the context of preventive care and disease management.

### Turnaround Time

The turnaround time for a diagnostic test affects the speed of clinical decision-making. Some tests, such as cytology and in-house blood tests, provide results within minutes to hours. Other tests, such as histopathology and bacterial culture, require days to weeks. The clinician must consider the urgency of the clinical situation when selecting a test.

For a critically ill patient, the clinician may need to start treatment based on preliminary results while waiting for definitive results. For a stable patient, the clinician may choose a test with a longer turnaround time to obtain a definitive diagnosis.

## Practical Workflow for Test Selection

The following workflow provides a systematic approach to selecting a diagnostic test for a given presentation. This workflow is designed to be used in a clinical setting and can be adapted to the specific needs of the practice.

### Step 1: Define the Clinical Question

The first step is to define the clinical question. The clinician must determine what information is needed to make a clinical decision. This question should be specific and actionable. For example, the question might be, "Is this animal infected with a specific pathogen?" or "What type of cell is present in this mass?"

### Step 2: Rank the Differential Diagnoses

The second step is to rank the differential diagnoses based on the signalment, history, and physical examination findings. The clinician should consider the prevalence of each disease in the population and the severity of the clinical signs. The leading differential diagnosis is the one that is most likely and most important to confirm or exclude.

### Step 3: Select the Test

The third step is to select the test that best answers the clinical question. The clinician should consider the accuracy of the test, the cost, the invasiveness, and the turnaround time. The test should be selected based on its ability to discriminate between the leading differential diagnoses.

### Step 4: Interpret the Results

The fourth step is to interpret the results in the context of the clinical picture. The clinician should consider the sensitivity and specificity of the test, the pretest probability of disease, and the clinical signs. A positive result on a test with high specificity is strong evidence of disease, while a negative result on a test with high sensitivity is strong evidence against disease.

### Step 5: Escalate if Necessary

The fifth step is to escalate the diagnostic workup if the results are ambiguous or if the clinical picture does not match the test results. The clinician may need to repeat the test, choose a different test, or refer the patient to a specialist for advanced diagnostics.

## Serology vs. PCR for Infectious Disease

The choice between serology and PCR is a common decision in veterinary practice. Both tests are used to diagnose infectious diseases, but they answer different clinical questions.

### Serology

Serology detects antibodies produced by the host in response to infection or vaccination. The presence of antibodies indicates that the host has been exposed to the pathogen, but it does not necessarily indicate active infection. Antibodies may persist for months or years after the infection has resolved, and vaccination can produce antibodies that are indistinguishable from those produced by natural infection.

Serology is useful for screening for exposure to a pathogen, for confirming a diagnosis in a patient with clinical signs, and for monitoring the response to vaccination. The timing of the sample collection is important. A single sample may not be sufficient to distinguish between acute and past infection. A paired sample, taken two to four weeks apart, can demonstrate a rising antibody titer, which is evidence of active infection.

### PCR

PCR detects the genetic material of the pathogen itself. A positive PCR result indicates that the pathogen is present in the sample. PCR is highly sensitive and can detect small amounts of the pathogen, but it requires the pathogen to be present in the sample at the time of collection. A negative PCR result does not rule out infection if the pathogen is present in a different location or if the sample was collected at a time when the pathogen was not present.

PCR is useful for confirming an active infection, for identifying the specific strain of the pathogen, and for monitoring the response to treatment. The timing of the sample collection is critical. PCR may be negative in the early stages of infection before the pathogen has reached detectable levels in the sample.

### Choosing Between Serology and PCR

The choice between serology and PCR depends on the clinical question. If the question is about exposure or immunity, serology is the appropriate test. If the question is about active infection, PCR is the appropriate test. The clinician should also consider the cost and turnaround time of each test.

The Merck Veterinary Manual provides background on the clinical presentation of infectious diseases and the diagnostic approaches used in veterinary practice. This resource helps the clinician understand the strengths and limitations of each test for specific pathogens.

## Cytology vs. Histopathology for Masses

The evaluation of a mass lesion is a common clinical problem in veterinary practice. The choice between cytology and histopathology depends on the clinical question and the nature of the mass.

### Cytology

Cytology involves the microscopic examination of cells obtained from a mass or fluid sample. The sample is typically collected by fine-needle aspiration, which is minimally invasive and can be performed in the clinic. Cytology provides a rapid assessment of the cell types present and can distinguish between inflammatory, infectious, and neoplastic processes.

Cytology is useful for the initial evaluation of a mass. It can provide a preliminary diagnosis and help the clinician decide whether further testing is needed. However, cytology has limitations. It does not provide information about the tissue architecture, and it may not be able to distinguish between benign and malignant neoplasms.

### Histopathology

Histopathology involves the microscopic examination of a tissue sample that has been fixed, embedded, and stained. The sample is typically collected by biopsy, which may be performed surgically or with a needle. Histopathology provides a definitive diagnosis based on the tissue architecture and the cellular characteristics.

Histopathology is the gold standard for the diagnosis of neoplastic diseases. It can distinguish between benign and malignant neoplasms, identify the tissue of origin, and provide information about the grade of the tumor. Histopathology is also useful for the diagnosis of inflammatory diseases and infectious diseases.

### Choosing Between Cytology and Histopathology

The choice between cytology and histopathology depends on the clinical question and the nature of the mass. If the clinician needs a quick answer to guide the initial management, cytology is the appropriate test. If the clinician needs a definitive diagnosis to plan treatment, histopathology is the appropriate test.

The clinical situation also affects the choice. For a small, superficial mass, a fine-needle aspirate may be sufficient. For a large, deep mass, a surgical biopsy may be required. The clinician should consider the risk of the procedure and the cost to the owner.

## Endocrine Testing

Endocrine diseases require a different approach to diagnostic testing. The clinical question is about hormone levels and the function of the endocrine gland.

### Thyroid Testing

Hypothyroidism is a common endocrine disease in dogs. The diagnosis is based on the measurement of thyroid hormone levels, including total thyroxine (T4) and free thyroxine (fT4). A low T4 level is suggestive of hypothyroidism, but it can also be seen in sick animals with non-thyroidal illness. A low fT4 level is more specific for hypothyroidism.

The diagnosis of hypothyroidism may require additional testing, such as a thyroid-stimulating hormone (TSH) level. A high TSH level with a low T4 level is consistent with hypothyroidism. The clinician should interpret the results in the context of the clinical signs and the results of other tests.

### Adrenal Testing

Hyperadrenocorticism, also known as Cushing's syndrome, is a common endocrine disease in dogs. The diagnosis is based on the measurement of cortisol levels and the response to dynamic testing. The ACTH stimulation test and the low-dose dexamethasone suppression test are the two most common tests.

The ACTH stimulation test measures the cortisol response to the administration of synthetic ACTH. The low-dose dexamethasone suppression test measures the cortisol response to the administration of dexamethasone. The choice of test depends on the clinical presentation and the suspected cause of the disease.

The Merck Veterinary Manual provides background on the clinical presentation of endocrine diseases and the diagnostic approaches used in veterinary practice. The clinician should use this background to interpret the results of endocrine testing in the context of the patient's clinical signs.

## Culture and Sensitivity Testing

Culture and sensitivity testing is essential for the management of bacterial infections. The test identifies the bacteria present in a sample and determines which antibiotics are effective against the bacteria.

### Sample Collection

The quality of the culture result depends on the quality of the sample. The sample should be collected from the site of infection using a sterile technique. The sample should be transported to the laboratory in a sterile container and processed as soon as possible.

### Interpretation of Results

The culture result identifies the bacteria present in the sample. The sensitivity result indicates which antibiotics are effective against the bacteria. The clinician should use the results to guide the choice of antibiotic therapy.

Culture and sensitivity testing is particularly important for infections that have failed to respond to treatment, for chronic infections, and for infections that are likely to be resistant to antibiotics. The World Organisation for Animal Health provides official guidance on the use of antimicrobials and the importance of culture and sensitivity testing for the management of antimicrobial resistance.

## Point-of-Care Testing

Point-of-care testing refers to diagnostic tests that can be performed in the clinic and provide results within minutes. These tests are useful for the rapid assessment of a patient and for the monitoring of treatment.

### Common Point-of-Care Tests

Common point-of-care tests include blood glucose, blood urea nitrogen, creatinine, and electrolyte panels. These tests are useful for the assessment of a patient with a metabolic disease or for the monitoring of a patient with a chronic disease.

### Limitations of Point-of-Care Testing

Point-of-care tests have limitations. They may be less accurate than laboratory tests, and they may not provide the same level of detail. The clinician should interpret the results of point-of-care tests in the context of the clinical picture and confirm the results with laboratory tests when necessary.

The American Animal Hospital Association provides guidelines for the use of point-of-care testing in veterinary practice. These guidelines help the clinician understand the strengths and limitations of point-of-care tests and how to use them effectively.

## Common Failure Patterns

The selection of a diagnostic test can fail for several reasons. The following are common failure patterns in veterinary practice.

### Failure to Define the Clinical Question

The most common failure is the failure to define the clinical question. The clinician may order a test without a clear question in mind, which can lead to a result that is not useful for the clinical decision. The clinician should always define the clinical question before ordering a test.

### Failure to Consider the Test Characteristics

The clinician may fail to consider the sensitivity and specificity of the test. A test with low sensitivity may miss a disease, while a test with low specificity may produce false positives. The clinician should consider the test characteristics when selecting a test.

### Failure to Consider the Timing of the Test

The clinician may fail to consider the timing of the test. Serology may be negative in the early stages of infection, and PCR may be negative if the pathogen is not present in the sample. The clinician should consider the timing of the test relative to the onset of the disease.

### Failure to Interpret the Results in Context

The clinician may fail to interpret the results in the context of the clinical picture. A positive result on a test with low specificity may be a false positive, and a negative result on a test with low sensitivity may be a false negative. The clinician should interpret the results in the context of the clinical signs and the pretest probability of the disease.

## Records and Measurements

The following records and measurements are important for the use of diagnostic tests in veterinary practice.

### Patient Records

The patient record should include the signalment, the clinical signs, the results of the physical examination, and the results of the diagnostic tests. The record should also include the clinical question and the rationale for the choice of test.

### Test Results

The test results should be recorded in the patient record, including the date of the test, the type of test, and the result. The results should be interpreted in the context of the clinical picture and the test characteristics.

### Quality Control

The practice should have a quality control program for the use of diagnostic tests. The program should include the calibration of the equipment, the training of the staff, and the review of the test results.

## Welfare and Safety Context

The welfare of the patient is an important consideration in the choice of a diagnostic test. The clinician should consider the risk of the procedure to the patient and the potential for pain or distress. The clinician should also consider the welfare of the patient in the context of the disease and the treatment.

The World Organisation for Animal Health provides a guidance on the welfare of animals in the context of animal health and welfare. The clinician should consider the welfare of the patient when choosing a diagnostic test.

## Professional Escalation Criteria

The clinician should escalate the diagnostic workup to a specialist in the following situations.

### When the Results Are Ambiguous

If the results of the diagnostic test are ambiguous or do not match the clinical picture, the clinician should consider a referral to a specialist. The specialist may have access to additional tests or may be able to interpret the results in a different context.

### When the Disease Is Complex

If the disease is complex or the diagnosis is difficult, the clinician should consider a referral to a specialist. The specialist may have experience with the disease and may be able to provide a more accurate diagnosis.

### When the Treatment Is Not Working

If the treatment is not working, the clinician should consider a referral to a specialist. The specialist may be able to identify the cause of the failure and recommend a different treatment.

## A Structured Record System for Diagnostic Test Selection

A recurring source of diagnostic error in veterinary practice is not the choice of a single test but the absence of a structured record that tracks the reasoning behind each test selection. When a case becomes complex, spans multiple visits, or involves a referral, the original clinical question and the rationale for test selection are often lost. This section provides a practical record system that documents the diagnostic pathway from the first presentation to the final interpretation, allowing the clinician to audit decisions, identify errors, and communicate the case to colleagues or specialists.

### The Diagnostic Decision Record

The diagnostic decision record is a structured document that captures the clinical reasoning at each step of the diagnostic process. It is not a substitute for the medical record but a supplement that focuses specifically on the diagnostic pathway. The record should be initiated at the first consultation and updated at each subsequent visit or when new test results become available.

The record consists of six fields that correspond to the steps of the clinical decision framework. Each field is designed to be completed in a few minutes during the consultation. The fields are the clinical question, the ranked differentials, the selected test, the test rationale, the result interpretation, and the next action. The record should be stored in the patient file and reviewed when the diagnostic pathway becomes complex or when the results do not match the clinical picture.

The first field, the clinical question, is a single sentence that states what the clinician needs to know to make a treatment decision. For example, the question might be, "Does this dog have an active Leptospira infection that requires antibiotic therapy?" or "Is this splenic mass a hemangiosarcoma or a benign hematoma?" The question must be specific and actionable. A vague question such as "What is wrong with this patient?" does not provide a basis for test selection.

The second field, the ranked differential tests, lists the leading differential diagnoses in order of likelihood. The ranking is based on the signalment, history, physical examination findings, and the prevalence of each disease in the local population. The ranking should be reviewed at each visit because new information can change the order of the differentials.

The third field, the selected test, records the test that was chosen and the reason for the choice. The reason should reference the clinical question and the test characteristics. For example, "PCR was selected because the clinical question is about active infection and PCR detects the pathogen directly" or "Cytology was selected because the mass is superficial and a rapid preliminary classification is needed."

The fourth field, the test result, records the result of the test in the context of the clinical question. The result should be recorded as positive, negative, or ambiguous, with the actual value or finding noted. The result should not be interpreted in isolation but in the context of the clinical question and the test characteristics.

The fifth field, the result interpretation, records the clinician's interpretation of the result in the context of the clinical picture. This field should include the pretest probability of the disease, the sensitivity and specificity of the test, and the clinical signs. For example, "The PCR result was negative, but the pretest probability of infection was high because the patient had a fever and a history of exposure. The negative result does not exclude infection because the sample was collected from a site that may not contain the pathogen."

The sixth field, the next step, records the action that will be taken based on the interpretation. The next step may be to start treatment, to repeat the test, to select a different test, or to refer the patient to a specialist. The next step should be specific and actionable.

### Implementing the Record in Practice

The diagnostic decision record can be implemented in a paper or electronic format. The record should be integrated into the practice's existing medical record system so that it is accessible to all clinicians who see the patient. The record should be reviewed at each visit and updated when new information becomes available.

The implementation of the record system requires a commitment from the practice to use the record consistently. The record is most useful when it is completed at the time of the consultation, not at the end of the day. The clinician should complete the first three fields during the consultation and the remaining fields when the test results are available.

The practice should designate a staff member to monitor the use of the record and to provide feedback to the clinicians. The staff member can review the records at regular intervals to identify patterns of diagnostic error, such as the repeated selection of a test with low sensitivity for a particular condition or the failure to escalate the diagnostic workup when the results are ambiguous.

The record system is particularly useful for cases that involve multiple tests over a period of time. For example, a patient with a chronic skin condition may have a cytology, a culture, and a biopsy over several weeks. The record provides a timeline of the diagnostic pathway and helps the clinician to see the progression of the diagnostic workup.

### Using the Record for Troubleshooting

The record system provides a structured method for troubleshooting when the diagnostic pathway fails. When a test result does not match the clinical picture, the clinician can review the record to identify the source of the error. The review should focus on the clinical question, the test selection, and the result interpretation.

The first step in the troubleshooting process is to review the clinical question. The question may have been too broad or too narrow. For example, the question "Is this patient infected?" is too broad because it does not specify the pathogen or the site of infection. The question "Is this patient infected with a specific pathogen?" is more useful because it provides a basis for test selection.

The second step is to review the test selection. The test may not have been appropriate for the clinical question. For example, a serology test may have been selected when the clinical question was about active infection, but serology cannot distinguish active infection from past exposure. The test may also have been selected without considering the timing of the test relative to the onset of the disease.

The third step is to review the result interpretation. The result may have been interpreted without considering the pretest probability of the disease or the test characteristics. For example, a positive result on a test with low specificity may have been interpreted as a confirmed diagnosis when the result was a false positive.

The record system also provides a method for troubleshooting the diagnostic pathway as a whole. The clinician can review the sequence of tests to identify patterns of failure. For example, the clinician may have repeated the same test multiple times without changing the test selection, or the clinician may have escalated to a more invasive test without first exhausting the less invasive options.

### The Diagnostic Pathway Log

The diagnostic pathway log is a companion to the diagnostic decision record. The log is a chronological list of all the diagnostic tests that were performed for a patient, including the date of the test, the type of test, the sample type, the laboratory, and the result. The log provides a summary of the diagnostic pathway and is useful for the review of the case.

The log should be maintained for every patient who undergoes diagnostic testing. The log should be updated when a test is performed and when the result is available. The log should be reviewed at the end of the diagnostic workup to identify the sequence of tests and the time between the tests.

The log is particularly useful for the referral of a patient to a specialist. The specialist can review the log to understand the diagnostic pathway and to identify the tests that have already been performed. The specialist can then select the next test based on the results of the previous tests.

The log also provides a record of the diagnostic pathway for the owner. The owner can see the sequence of tests and the results, which can help the owner to understand the diagnostic process and the cost of the tests. The American Veterinary Medical Association provides resources for pet owners about the importance of regular veterinary visits and the value of diagnostic testing, which can be used to support the owner's understanding of the diagnostic pathway.

### Common Failure Patterns in the Record

The record system can identify common failure patterns in the diagnostic process. The following patterns are frequently observed in veterinary practice.

The first failure pattern is the failure to define the clinical question. The record may show that the clinical question was vague or that the question was not recorded. The clinician may have ordered a test without a clear question in mind, which can lead to a result that is not useful for the clinical decision.

The second failure pattern is the failure to consider the test characteristics. The record may show that the test was selected without considering the sensitivity and specificity of the test. The clinician may have selected a test with low sensitivity for a disease that requires a high sensitivity test, or a test with low specificity for a disease that requires a high specificity test.

The third failure pattern is the failure to consider the timing of the test. The record may show that the test was performed at a time when the result was likely to be negative. For example, a serology test may have been performed in the early stages of infection before the host had produced detectable antibodies.

The fourth failure pattern is the failure to interpret the results in context. The record may show that the result was interpreted without considering the pretest probability of the disease or the clinical picture. The clinician may have interpreted a positive result on a test with low specificity as a confirmed diagnosis when the result was a false positive.

The fifth failure pattern is the failure to escalate the diagnostic workup. The record may show that the clinician repeated the same test multiple times without changing the test selection, or that the clinician did not refer the patient to a specialist when the results were ambiguous.

### Using the Record for Professional Escalation

The record system provides a structured basis for the escalation of the diagnostic workup to a specialist. When the results are ambiguous or the disease is complex, the clinician can use the record to prepare a referral. The record provides the specialist with the clinical question, the ranked differentials, the tests performed, and the results. The specialist can use the record to understand the diagnostic pathway and to select the next test.

The record also provides a basis for the discussion of the case with the owner. The clinician can use the record to explain the diagnostic process and the rationale for the test selection. The record can help the owner to understand the cost of the diagnostic and the value of the tests.

The World Small Animal Veterinary Association provides global guidelines for the clinical practice, including the use of diagnostic tests in the context of preventive care and disease management. The guidelines support the use of a structured approach to the diagnostic process and the importance of the clinical reasoning in the test selection.

### Records and Measurements for the Diagnostic Decision Record

The diagnostic decision record should be reviewed at regular intervals to identify patterns of diagnostic error. The practice should designate a staff member to review the records and to report the findings to the clinicians. The review should focus on the following measurements.

The first measurement is the percentage of records that include a specific clinical question. A low percentage indicates that the clinicians are not defining the clinical question before ordering a test.

The second measurement is the percentage of records that include a ranked differential diagnosis. A low percentage indicates that the clinicians are not considering the differential diagnoses before selecting a test.

The third measurement is the percentage of records that include a rationale for the test selection. A low percentage indicates that the clinicians are not considering the test characteristics when selecting a test.

The fourth measurement is the percentage of records that include a result interpretation. A low percentage indicates that the clinicians are not interpreting the results in the context of the clinical picture.

The fifth measurement is the percentage of records that include a next action. A low percentage indicates that the clinicians are not planning the next step in the diagnostic pathway.

The practice should use the measurements to identify the areas of the diagnostic process that need improvement. The practice should provide training to the clinicians on the use of the record and the interpretation of the test results.

The Cornell University College of Veterinary Medicine provides educational resources for the veterinary profession, including the clinical reasoning and the diagnostic decision-making. These resources can be used to support the training of the clinicians in the use of the diagnostic decision record.

### The Record in the Context of the Practice

The diagnostic decision record is a practical tool that can be implemented in any veterinary practice. The record does not require a specific software or a specific laboratory. The record can be used with the existing medical record system and the existing laboratory services.

The record is most useful when the practice has a culture of the clinical reasoning and the quality improvement. The practice should encourage the clinicians to use the record and to review the records at regular intervals. The practice should also provide the clinicians with the training and the resources to use the record effectively.

The record system is a complement to the clinical decision framework. The framework provides the steps for the test selection, and the record provides the documentation of the steps. The record helps the clinician to be consistent in the application of the framework and to identify the areas of the diagnostic process that need improvement.

The record also provides a basis for the communication with the owner. The clinician can use the record to explain the diagnostic process and the cost of the tests. The record can help the owner to understand the value of the diagnostic and the importance of the follow-up.

The American Animal Hospital Association provides practice guidance for the companion-animal care, including the preventive care and the life-stage considerations. The guidelines support the use of the structured diagnostic in the practice and the importance of the clinical decision.

### The Record as a Teaching Tool

The diagnostic decision record can be used as a teaching tool for the veterinary students and the new graduates. The record provides a structured approach to the diagnostic decision-making and helps the learner to understand the clinical reasoning behind the test selection.

The record can be used in the clinical rounds to review the diagnostic pathway of a patient. The clinician can present the record to the students and the discussion of the clinical question, the test selection, and the result interpretation. The record can also be used to identify the common failure patterns and to discuss the strategies for the improvement.

The World Small Animal Veterinary Association provides global guidelines for the clinical practice, which include the use of the diagnostic in the veterinary education. The guidelines support the use of the record as a teaching tool for the clinical reasoning.

The record system is a practical tool that can be implemented in any practice. The record provides a structured approach to the diagnostic decision-making and helps the clinician to identify the errors and to improve the quality of the diagnostic. The record is a complement to the clinical decision framework and provides the documentation of the clinical reasoning.

## Frequently Asked Questions

### What is the difference between a screening test and a diagnostic test?

A screening test is used to detect a disease in a population that does not have clinical signs. A diagnostic test is used to confirm or exclude a disease in a patient with clinical signs. Screening tests are often less accurate than diagnostic tests, but they are useful for identifying patients who need further testing.

### How do I choose between a serology test and a PCR test?

The choice between serology and PCR depends on the clinical question. Serology detects antibodies and is useful for assessing exposure or immunity. PCR detects the genetic material of the pathogen and is useful for confirming an active infection. The clinician should consider the timing of the test and the cost of the test.

### What is the difference between cytology and histopathology?

Cytology involves the examination of cells collected from a mass lesion. Histopathology involves the examination of a tissue sample. Cytology is faster and less invasive, but histopathology provides a definitive diagnosis based on the tissue architecture.

### When should I use a culture and sensitivity test?

A culture and sensitivity test should be used when a bacterial infection is suspected and the choice of antibiotic is not clear. The test identifies the bacteria present and provides information about the antibiotics that are effective against the bacteria.

### What is the role of point-of-care testing in veterinary practice?

Point-of-care testing provides rapid results in the clinic. It is useful for the initial assessment of a patient and for the monitoring of a patient with a chronic disease. The results of point-of-care tests should be confirmed with laboratory tests when necessary.

### How do I interpret a positive result on a test with low specificity?

A positive result on a test with low specificity may be a false positive. The clinician should consider the pretest probability of the disease and the clinical picture when interpreting the result. A confirmatory test with higher specificity may be needed.

### How do I interpret a negative result on a test with low sensitivity?

A negative result on a test with low sensitivity may be a false negative. The clinician should consider the pretest probability of the disease and the clinical picture when interpreting the result. A confirmatory test with higher sensitivity may be needed.

### When should I refer a patient to a specialist?

The clinician should refer a patient to a specialist when the diagnostic is ambiguous, when the disease is complex, or when the treatment is not working. The specialist may have access to additional tests or may be able to interpret the results in a different context.

## Using the Evidence

| Source | Best use in this topic | Important limitation |
|---|---|---|
| [Pet Care](https://www.avma.org/resources-tools/pet-owners) | official guidance | Check the linked page for current local requirements |
| [AAHA Guidelines](https://www.aaha.org/resources) | official guidance | Check the linked page for current local requirements |
| [Global Guidelines](https://wsava.org/global-guidelines) | official guidance | Check the linked page for current local requirements |

## Related Veterinary Guides

- [Decision Framework for Choosing Antifungal Therapy in Veterinary Patients](/knowledge/veterinary-medicine/veterinary-pathology-microbiology/decision-framework-antifungal-therapy-veterinary)
- [Conducting Systematic Reviews of Veterinary Diagnostic Test Accuracy](/knowledge/veterinary-medicine/veterinary-research-methods/conducting-systematic-reviews-veterinary-diagnostic-test-accuracy)
- [Diagnostic Cytology: Sample Collection and Interpretation](/knowledge/veterinary-medicine/veterinary-pathology-microbiology/diagnostic-cytology-sample-collection-and-interpretation)
- [Cytology of Lymph Nodes: Diagnostic Approach to Lymphadenopathy](/knowledge/veterinary-medicine/clinical-pathology/cytology-lymph-nodes-diagnostic)
- [Toxicology in Emergency Practice: Common Poisons and Diagnostic Approach](/knowledge/veterinary-medicine/emergency-critical-care/toxicology-emergency-practice-common-poisons-diagnostic-approach)

## References and Further Reading

- [Pet Care](https://www.avma.org/resources-tools/pet-owners). American Veterinary Medical Association.
- [AAHA Guidelines](https://www.aaha.org/resources). American Animal Hospital Association.
- [Global Guidelines](https://wsava.org/global-guidelines). World Small Animal Veterinary Association.
- [Merck Veterinary Manual](https://www.merckvetmanual.com/). Merck Veterinary Manual.
- [Cornell University College of Veterinary Medicine](https://www.vet.cornell.edu/). Cornell University.
- [Animal Health and Welfare](https://www.woah.org/en/what-we-do/animal-health-and-welfare). World Organisation for Animal Health.
- [Special Issue on Digital Pathology, Tissue Image Analysis, Artificial Intelligence, and Machine Learning: Approximation of the Effect of Novel Technologies on Toxicologic Pathology.](https://pubmed.ncbi.nlm.nih.gov/33840332). Toxicologic pathology, 2021.
- [Automated diagnosis of 7 canine skin tumors using machine learning on H&E-stained whole slide images.](https://pubmed.ncbi.nlm.nih.gov/37515411). Veterinary pathology, 2023.
- [Automatic Oral Cancer Detection Using Improved Honey Badger Algorithm-Based Feature Selection.](https://pubmed.ncbi.nlm.nih.gov/42449751). Diagnostics (Basel, Switzerland), 2026.
- [Lipidomics as a Diagnostic Tool for Prostate Cancer.](https://pubmed.ncbi.nlm.nih.gov/33919225). Cancers, 2021.
- [Estimation of the accuracy of an ELISA test applied to bulk tank milk for predicting herd-level status for Salmonella Dublin in dairy herds using Bayesian Latent Class Models.](https://pubmed.ncbi.nlm.nih.gov/35780658). Preventive veterinary medicine, 2022.

> This article is educational and is not a substitute for veterinary diagnosis or treatment. Contact a veterinarian for advice about an individual animal.