# Common Pitfalls in Veterinary Cytology ## Quick Answer - Cytology errors that lead to misdiagnosis most often arise from sample collection, preparation, and interpretation, not from the patient's disease itself. - The practical next step is to establish a standardized collection and staining protocol and to confirm any uncertain diagnosis with histopathology. - A key limitation is that cytology cannot define tissue architecture, so some benign and malignant processes remain indistinguishable without biopsy. ## Understanding the Role of Cytology in Veterinary Diagnosis Cytology is a diagnostic method that examines individual cells collected from lesions, body fluids, or tissue surfaces. It is a rapid, minimally invasive tool that provides preliminary information about inflammation, infection, and neoplasia. In veterinary practice, cytology is often the first step in evaluating a mass or effusion because it can be performed in the clinic with basic equipment and yields results within minutes. The value of cytology depends on the quality of the sample and the skill of the interpreter. A well-prepared smear that is representative of the lesion can guide the next diagnostic step, whether that is surgical biopsy, culture, or medical therapy. A poorly prepared or misinterpreted smear can lead to an incorrect diagnosis and inappropriate patient management. The American Veterinary Medical Association emphasizes that pet owners should work with their veterinarian to understand the purpose of diagnostic tests and the meaning of results, which underscores the importance of accurate laboratory information in clinical decision making. Cytology is not a substitute for histopathology. Histopathology examines intact tissue architecture and provides information about invasion and organization that cytology cannot. When cytology results conflict with clinical findings, or when the sample is inadequate, histopathology is the appropriate next step. The Merck Veterinary Manual provides background on the use of laboratory tests in veterinary diagnosis and notes that test results must be interpreted in the context of the patient's history and physical examination. ## At a Glance: Common Pitfalls and Prevention The table below summarizes the most frequent cytology pitfalls, their typical causes, and the practical steps that reduce their occurrence. | Pitfall | Typical Cause | Prevention Strategy | | --- | --- | --- | | Hemodilution | Excessive blood contamination during aspiration | Use gentle suction, stop when blood appears, and prepare smears from the needle hub | | Crush artifact | Excessive pressure during smear preparation | Use a coverslip or pull-apart technique with minimal pressure | | Stain precipitate | Inadequate washing or expired stain | Filter stains, change solutions regularly, and rinse slides thoroughly | | Overinterpretation of reactive mesothelial cells | Confusing reactive cells with malignant cells | Recognize that mesothelial cells can appear atypical after inflammation or fluid accumulation | | Air-drying delay | Smears left exposed before fixation | Fix or dry smears promptly according to the stain protocol | | Thick smear | Too much sample on the slide | Use a small drop and spread it evenly | | Degenerate cells | Delayed processing or improper storage | Process samples promptly and store slides in a dry, clean container | ## Sample Collection and Preparation Errors ### Hemodilution and Blood Contamination Hemodilution occurs when the sample contains a large number of red blood cells that dilute the cells of interest. This is a common problem when aspirating vascular lesions or when the needle passes through a blood vessel before entering the target tissue. The result is a smear that is difficult to interpret because the diagnostic cells are sparse and obscured by blood. The veterinarian can reduce hemodilution by using a smaller needle, applying gentle suction, and withdrawing the needle as soon as blood appears in the hub. In some cases, a nonaspiration technique, where the needle is moved within the tissue without suction, produces a less bloody sample. The sample should be expressed onto a slide from the needle hub instead of from the syringe, because the hub contains the most concentrated portion of the aspirate. When blood contamination is unavoidable, the smear can still be useful if the diagnostic cells are present in sufficient numbers. The interpreter should note the degree of hemodilution in the report and consider whether a repeat aspirate or a biopsy is needed. The Merck Veterinary Manual describes the general approach to sample collection and preparation for cytology, and it emphasizes that the quality of the smear directly affects the reliability of the interpretation. ### Crush Artifact Crush artifact occurs when the cells are damaged by excessive pressure during smear preparation. The cells appear distorted, with ruptured membranes and smeared nuclei, which makes it difficult to assess cell size, nuclear to cytoplasmic ratio, and other features that are important for distinguishing benign from malignant cells. Crush artifact is most common when the smear is made with a heavy hand or when the sample is too thick. The preparation technique should use a gentle, even pressure. A common method is the two-slide pull or the coverslip method, where the sample is spread with a single, smooth motion. The goal is to create a monolayer of cells that are intact and evenly distributed. If the sample is too thick, the slide can be discarded and a new smear prepared from the remaining sample. The interpreter should recognize crush artifact and avoid making a diagnosis based on damaged cells. If the smear is too damaged, the veterinarian should repeat the aspirate or proceed to biopsy. The Cornell University College of Veterinary Medicine provides educational materials on sample preparation and interpretation that emphasize the importance of a well-prepared smear. ### Stain Precipitate and Staining Artifacts Stain precipitate appears as dark, granular deposits on the smear that can be mistaken for bacteria, fungal elements, or nuclear debris. It is caused by undissolved stain crystals, contamination of the stain with water or other solutions, or inadequate washing after staining. The precipitate can obscure the cells and lead to a false diagnosis of infection or neoplasia. The prevention of stain precipitate requires proper stain maintenance. The stain should be filtered regularly, the containers should be covered to prevent evaporation and contamination, and the slides should be rinsed thoroughly after staining. The staining protocol should be followed exactly, and the stain should be replaced according to the manufacturer's recommendations. When precipitate is present, the interpreter should examine the smear for the pattern of the deposit. Precipitate is often distributed evenly across the slide, while bacteria are associated with cells or are present in a specific pattern. If the precipitate is severe, the slide should be restained or the sample should be repeated. ## Interpretation Errors and Overdiagnosis ### Overinterpretation of Reactive Mesothelial Cells Reactive mesothelial cells are a common source of confusion in cytology. These cells line the body cavities and can become enlarged and atypical in response to inflammation, infection, or the presence of fluid. They can appear similar to malignant cells, with a high nuclear to cytoplasmic ratio and prominent nucleoli, which can lead to a false diagnosis of carcinoma. The interpreter must consider the clinical context when evaluating mesothelial cells. Reactive mesothelial cells are often present in effusions that are associated with inflammation, heart failure, or other nonneoplastic conditions. The presence of a mixed population of cells, including inflammatory cells, supports a reactive process. Malignant cells, in contrast, are often more uniform and may form clusters or acinar structures. When the cytology is ambiguous, the veterinarian should recommend a biopsy or a second opinion from a clinical pathologist. The Merck Veterinary Manual provides guidance on the interpretation of effusions and the limitations of cytology in distinguishing reactive from malignant cells. ### Misclassification of Inflammatory Cells Inflammatory cells can be misclassified when the smear is poorly prepared or when the cells are degenerate. Neutrophils, macrophages, and lymphocytes have distinct morphologies, but they can be difficult to identify when the cells are damaged or when the smear is too thick. A misclassification can lead to an incorrect diagnosis of the underlying process, such as a bacterial infection versus a sterile inflammation. The interpreter should use a systematic approach to identify the cell types. The presence of a large number of neutrophils suggests a bacterial infection, while a mixed population of neutrophils and macrophages suggests a chronic inflammatory process. The presence of eosinophils may indicate a parasitic or allergic condition. The Merck Veterinary Manual provides a description of the inflammatory cell types and their clinical significance. When the cell type is uncertain, the veterinarian should consider additional tests, such as a bacterial culture or a special stain. The cytology report should note the uncertainty and recommend the appropriate follow-up. ### Overdiagnosis of Malignancy Overdiagnosis of malignancy is a serious error that can lead to unnecessary surgery, chemotherapy, or euthanasia. The cytology can show cells that are atypical, but the atypical features may be due to inflammation, repair, or a benign process. The interpreter must use a conservative approach and only diagnose malignancy when the features are clear and consistent. The criteria for malignancy include a high nuclear to cytoplasmic ratio, anisocytosis, anisokaryosis, and the presence of prominent nucleoli. These features are not always present in malignant cells, and they can be present in benign cells. The interpreter should consider the entire smear and the clinical context before making a diagnosis. When the cytology is suspicious but not diagnostic, the veterinarian should recommend a biopsy. The biopsy provides the tissue architecture that is needed to confirm the diagnosis. The Cornell University of Veterinary Medicine provides educational materials on the cytology of neoplasia and the limitations of the technique. ## Sample Handling and Storage Errors ### Delayed Processing and Degeneration The cells in a cytology sample begin to degenerate as soon as the sample is collected. The degeneration is accelerated by heat, moisture, and the presence of blood. The cells lose their detail, and the nuclei become pyknotic or karyorrhectic, which makes the smear difficult to interpret. The sample should be processed as soon as possible after collection. If the sample cannot be processed immediately, it should be stored in a refrigerator or on a cold pack. The smear should be air-dried and fixed according to the protocol. The delay between collection and processing should be noted in the report. The interpreter should recognize the signs of degeneration and avoid making a diagnosis based on degenerate cells. If the sample is too degenerate, the veterinarian should repeat the aspirate. ### Improper Storage of Slides The slides should be stored in a clean, dry container to prevent contamination and damage. The slides should be labeled with the patient's name, the date, and the site of the sample. The slides should be protected from dust, moisture, and direct sunlight. The storage of the slides is important for the quality of the smear. The slides should be stored in a slide box or a slide folder, and they should be handled by the edges to avoid smudging the smear. The slides should be transported to the laboratory in a rigid container to prevent breakage. The laboratory should be informed of the storage conditions and the time between collection and processing. The Merck Veterinary Manual provides guidance on the submission of samples to the laboratory and the importance of proper labeling and handling. ## Quality Control and Standardization The quality of the cytology is improved by a standardized protocol for collection, preparation, and staining. The protocol should be written and followed by all members of the practice. The protocol should include the type of needle and syringe, the number of passes, the preparation method, and the staining schedule. The practice should have a quality control program that includes the regular review of smears and the comparison of cytology results with histology results. The program should identify the common errors and the areas for improvement. The program should also include the training of new staff and the continuing education of the existing staff. The quality control program should be documented, and the results should be reviewed by the practice manager or the lead veterinarian. The program should be updated as new techniques and guidelines are introduced. The American Animal Hospital Association provides guidance on the standards of care in veterinary practice, including the importance of diagnostic testing and quality assurance. ## Common Failure Patterns in Cytology Practice The following patterns are common in practices that have a high rate of cytology errors. The patterns are not exhaustive, but they represent the most frequent causes of misdiagnosis. ### Failure to Correlate with Clinical Findings The cytology result is interpreted in isolation, without consideration of the patient's history, physical examination, and other test results. The result is then used to make a diagnosis that is inconsistent with the clinical picture. The error is common when the cytology is performed by a technician or a veterinarian who is not familiar with the patient. The solution is to review the cytology result in the context of the patient. The veterinarian should ask whether the result is consistent with the clinical findings. If the result is not consistent, the veterinarian should repeat the aspirate or proceed to biopsy. ### Failure to Use a Clinical Pathologist The cytology is interpreted by a general practitioner who does not have the training or experience to identify the subtle features of the cells. The result is then a misdiagnosis that is not recognized until the patient fails to respond to treatment. The solution is to use a clinical pathologist for the interpretation of the cytology. The pathologist has the training and experience to identify the cells and to provide a differential diagnosis. The pathologist can also provide a second opinion on the smears that are ambiguous. ### Failure to Document the Cytology The cytology result is not documented in the medical record. The result is then lost, and the patient is not followed up. The error is to the result in the record, which is a legal and professional requirement. The solution is to document the cytology result in the medical record, including the date, the site, the preparation method, and the interpretation. The documentation should be complete and accurate, and it should be signed by the veterinarian. ## Practical Implementation and Assessment Steps The following steps are a practical approach to improving the quality of cytology in a veterinary practice. The steps are based on the principles of quality control and the common failure patterns. 1. Review the current cytology protocol and identify the areas that are not standardized. 2. Develop a written protocol for the collection, preparation, and staining of cytology samples. 3. Train all staff members in the protocol and the proper technique. 4. Implement a quality control program that includes the regular review of smears. 5. Compare the cytology results with the histology results to identify the errors. 6. Use a clinical pathologist for the interpretation of the cytology. 7. Document the cytology results in the medical record. 8. Review the quality control data on a regular basis and update the protocol as needed. ## Records and Measurements The following records and measurements are important for the quality of cytology. The records should be kept for each patient and each sample. - The date and time of the collection. - The site of the collection. - The method of the collection. - The preparation method. - The staining method. - The interpretation of the smear. - The name of the interpreter. - The follow-up recommendation. The measurements that are important for the quality of cytology include the number of cells on the smear, the degree of hemodilution, the presence of the artifact, and the time between the collection and the processing. These measurements should be recorded and reviewed to identify the trends. ## Welfare and Safety Context The welfare of the patient is the primary concern in the collection of cytology samples. The collection should be performed with the least possible pain and distress. The patient should be restrained in a way that is safe for the patient and the staff. The collection should be performed by a trained professional. The safety of the staff is also important. The collection of cytology samples involves the use of needles and syringes, which can cause injury. The staff should be trained in the safe handling of the needles and the disposal of the sharps. The staff should also be aware of the risk of infection from the samples. The World Organisation for Animal Health provides guidance on the welfare of animals in veterinary practice, including the importance of the humane handling of animals during diagnostic procedures. ## Limitations of Cytology Cytology has several limitations that should be recognized by the veterinarian. The limitations are not a reason to avoid cytology, but they are a reason to use the technique appropriately. ### Inability to Assess Tissue Architecture Cytology cannot assess the architecture of the tissue. The cells are examined in isolation, and the relationship between the cells is not visible. The architecture is important for the diagnosis of some tumors, such as the distinction between a benign and a malignant tumor. ### Inability to Distinguish Some Benign and Malignant Cells Cytology cannot distinguish some benign and malignant cells. The cells may have a similar appearance, and the diagnosis is uncertain. The histology is needed to make the distinction. ### The Need for a Skilled Interpreter The cytology is only as good as the interpreter. The interpreter must have the training and experience to identify the cells and the artifacts. The interpreter must also be aware of the limitations of the technique. ## When to Escalate to a Specialist The veterinarian should escalate the cytology to a specialist in the following situations: - The cytology is ambiguous or the diagnosis is uncertain. - The cytology is not consistent with the clinical findings. - The cytology is not diagnostic because of the artifact or the degeneration. - The cytology is the basis for a major decision, such as the decision to treat or to euthanize. The specialist is a clinical pathologist or a veterinary oncologist. The specialist can provide a second opinion on the cytology and can recommend the next step in the diagnostic plan. ## A Structured Cytology Triage System for Daily Practice A recurring problem in veterinary cytology is not the absence of knowledge about artifacts and interpretation errors but the absence of a consistent method for deciding what to do when a smear is imperfect. Most practices handle cytology on a case by case basis, which leads to inconsistent decisions and missed opportunities to correct errors before they affect patient care. A structured triage system gives the veterinarian a repeatable path for evaluating smear quality, deciding whether a sample is adequate for interpretation, and determining the next step when the sample is not adequate. This system is distinct from the technical prevention strategies described earlier because it focuses on the decision process after the smear is on the slide. ### The Three Gate Assessment The triage system uses three sequential gates that every cytology smear must pass before a diagnostic interpretation is recorded. Each gate addresses a specific category of error and produces a clear outcome. The system is designed to be used at the microscope immediately after staining, while the patient is still in the building and a repeat sample is still possible. **Gate One: Cellular Adequacy** The first gate asks whether the smear contains enough intact diagnostic cells to support an interpretation. A smear with fewer than a threshold number of well preserved cells is not diagnostic regardless of how well it was stained or how carefully it was prepared. The veterinarian should scan the entire smear at low magnification before moving to high magnification. The question at this gate is not whether the cells are abnormal but whether there are enough cells to answer the clinical question. A smear that is too thick may contain many cells but they are stacked and impossible to evaluate individually. A smear that is too thin may contain only a few cells scattered across the slide. Both situations fail the adequacy gate. The veterinarian should also assess whether the cells are intact. A smear with many ruptured cells and free nuclei has lost the information needed for interpretation. When a smear fails Gate One, the correct action is to repeat the aspirate or collection. The veterinarian should adjust the technique based on the reason for the failure. A sparse smear suggests the needle did not enter the target tissue or the suction was too gentle. A thick smear suggests too much sample was expressed onto the slide. The repeat sample should be prepared with the specific correction in mind. **Gate Two: Artifact Assessment** The second gate asks whether the smear is free from artifacts that would distort the interpretation. The artifacts include hemodilution, crush artifact, stain precipitate, and degeneration. The veterinarian examines the smear for each artifact and records the degree of each one. The key question is whether the artifact is severe enough to compromise the interpretation. Mild hemodilution with a sufficient number of diagnostic cells does not fail the gate. The interpreter can work around the red blood cells and still identify the cells of interest. Severe hemodilution where the diagnostic cells are obscured or diluted below a usable number fails the gate. Crush artifact that distorts a small portion of the smear may be acceptable if intact cells are present in other areas. Crush artifact that affects the majority of the cells fails the gate. Stain precipitate is assessed by its distribution and quantity. A few scattered crystals do not prevent interpretation. Heavy precipitate that covers the cells or mimics bacteria fails the gate. The veterinarian should also check for air drying delay, which produces cells with a washed out appearance and indistinct nuclear detail. When a smear fails the artifact gate, the veterinarian has two options. The first is to prepare a new smear from the remaining sample if any is available. The second is to repeat the aspirate. The choice depends on the severity of the artifact and the availability of the patient. The key point is that the veterinarian does not proceed to interpretation with a smear that has significant artifact. **Gate Three: Clinical Correlation** The third gate asks whether the cytology result is consistent with the clinical findings. This gate is applied after the smear has passed the first two gates and an interpretation has been made. The veterinarian compares the cytology result with the history, physical examination findings, and any other diagnostic information that is available. A cytology result that is consistent with the clinical picture supports the diagnosis and allows the veterinarian to proceed with the appropriate management. A cytology result that is inconsistent with the clinical picture triggers a specific response. The veterinarian does not simply accept the cytology result and does not simply discard it. The veterinarian reviews the smear again, considers whether the sample was representative of the lesion, and decides whether a repeat sample or a biopsy is needed. The third gate is the most important for preventing misdiagnosis because it forces the veterinarian to consider the patient instead of the slide in isolation. The Merck Veterinary Manual emphasizes that laboratory test results must be interpreted in the context of the patient's history and physical examination. The third gate operationalizes this principle in a way that can be applied consistently. ### The Decision Matrix for Problematic Smears The triage system produces a clear set of outcomes that can be organized into a decision matrix. The matrix helps the veterinarian choose the next step based on which gate was failed and the clinical situation. | Gate Failed | Clinical Context | Recommended Action | | --- | --- | --- | | Gate One: Adequacy | Mass is accessible and patient is stable | Repeat aspirate with adjusted technique | | Gate One: Adequacy | Mass is deep or patient is unstable | Proceed to ultrasound guided aspirate or biopsy | | Gate Two: Artifact | Artifact is correctable with a new smear | Prepare a new smear from the remaining sample | | Gate Two: Artifact | Artifact is severe and no sample remains | Repeat the aspirate | | Gate Three: Consistency | Cytology is benign but clinical findings suggest malignancy | Repeat the aspirate or proceed to biopsy | | Gate Three: Consistency | Cytology is malignant but clinical findings are benign | Review the smear with a clinical pathologist | | Gate Three: Consistency | Cytology is ambiguous | Submit the smear to a clinical pathologist | The matrix is not a substitute for clinical judgment. It is a framework that ensures the veterinarian considers the relevant factors and does not skip a step. The matrix is particularly useful in a busy practice where the pressure to move to the next patient can lead to a hasty interpretation. ### The Cytology Quality Log A structured record system is essential for identifying patterns of error and improving the quality of cytology over time. The cytology quality log is a simple spreadsheet or paper form that records the outcome of each cytology sample. The log is not a replacement for the medical record but a separate quality assurance tool that is reviewed on a regular basis. The log should include the following fields for each sample: - Date of collection - Patient identification - Sample site - Collection method - Smear preparation method - Staining method - Gate One result: pass or fail - Gate Two result: pass or fail - Gate Three result: pass or fail - Final interpretation - Follow up action - Histology correlation if available The log is reviewed monthly by the lead veterinarian or the practice manager. The review focuses on the patterns that emerge. A high rate of Gate One failures suggests a problem with the collection technique. A high rate of Gate Two failures suggests a problem with the preparation or staining protocol. A high rate of Gate Three failures suggests a problem with the interpretation or with the clinical correlation. The log also provides the data for the comparison of cytology results with histology results. This comparison is the most direct measure of the accuracy of the cytology service. The practice can calculate the rate of agreement between cytology and histology and identify the cases where the cytology was incorrect. The review of these cases is a learning opportunity for the entire team. The American Animal Hospital Association provides guidance on the standards of care in veterinary practice, including the importance of diagnostic testing and quality assurance. The cytology log is a practical implementation of these standards. The log does not need to be complex. A simple spreadsheet or a paper form is sufficient. The value is in the regular review and the action taken on the findings. ### Troubleshooting the Nondiagnostic Smear When a smear fails the first or second gate, the veterinarian must decide whether to repeat the sample or to proceed with a different diagnostic approach. The decision is based on the reason for the failure and the clinical situation. **Sparse Smear** A sparse smear with few cells suggests that the needle did not reach the target tissue. The most common cause is a needle that is too short or a lesion that is deeper than expected. The veterinarian should palpate the lesion again and confirm the depth. A longer needle or a different approach angle may be needed. The suction may also be too gentle. The veterinarian should increase the suction slightly and make more passes through the lesion. **Thick Smear** A thick smear with too many cells suggests that too much sample was placed on the slide. The veterinarian should use a smaller drop of the sample and spread it more thinly. The preparation technique may also need to be adjusted. The coverslip method produces a thinner smear than the two slide method when the sample is viscous. **Bloody Smear** A bloody smear with hemodilution suggests that the needle passed through a blood vessel or that the lesion is vascular. The veterinarian should use a nonaspiration technique, where the needle is moved within the tissue without suction. This technique produces a less bloody sample because the cells enter the needle by capillary action. The veterinarian should also stop the aspiration as soon as blood appears in the hub. **Crushed Cells** A smear with crushed cells suggests that the pressure during preparation was too high. The veterinarian should use a lighter touch and a smoother motion. The coverslip method is gentler than the two slide method. The veterinarian should also avoid pressing down on the coverslip after the smear is made. **Stain Precipitate** A smear with stain precipitate suggests a problem with the stain. The veterinarian should filter the stain and check the washing protocol. The slides should be rinsed thoroughly after staining. The stain should be replaced if it is old or contaminated. ### The Escalation Protocol The escalation protocol defines when the veterinarian should involve a clinical pathologist or a specialist. The protocol is based on the three gate system and the clinical situation. The veterinarian should escalate the smear to a clinical pathologist in the following situations: - The smear passes the first two gates but the interpretation is ambiguous - The smear passes the first two gates but the interpretation is inconsistent with the clinical findings - The smear fails the third gate and the repeat sample is also inconsistent - The cytology result is the basis for a major decision such as surgery or euthanasia - The cytology result is the basis for a treatment decision that has significant side effects The clinical pathologist provides a second opinion on the smear and can identify features that the general practitioner may have missed. The pathologist can also recommend additional tests such as special stains or immunocytochemistry. The escalation protocol should be written and known to all members of the practice. The protocol should include the contact information for the clinical pathologist and the procedure for submitting the smear. The protocol should also include the expected turnaround time for the consultation. ### The Comparison with Histology The comparison of cytology results with histology results is the most important quality measure for a cytology service. The comparison is performed when a biopsy is taken from the same lesion that was aspirated. The cytology result and the histology result are compared and the agreement or disagreement is recorded. The comparison is recorded in the cytology log. The practice can then calculate the rate of agreement over time. A high rate of agreement indicates that the cytology service is accurate. A low rate of agreement indicates that the cytology service needs improvement. The review of the disagreements is the most valuable part of the comparison. The veterinarian should review the smear and the histology slide together to identify the reason for the disagreement. The reason may be a sampling error, where the aspirate did not reach the same area as the biopsy. The reason may be an interpretation error, where the veterinarian misidentified the cells. The reason may be a limitation of cytology, where the cells are not distinguishable without tissue architecture. The review of the disagreements should be documented and the findings should be used to improve the cytology service. The review may identify a need for additional training, a change in the collection technique, or a more conservative approach to interpretation. ### The Role of the Clinical Pathologist The clinical pathologist is a specialist in the interpretation of cytology and other laboratory tests. The pathologist has the training and experience to identify the subtle features of the cells and to provide a differential diagnosis. The pathologist can also provide a second opinion on the smears that are ambiguous. The use of the clinical pathologist is not a sign of weakness or a lack of skill. It is a sign of professional judgment and a commitment to the accuracy of the diagnosis. The pathologist is a member of the diagnostic team and should be consulted when the situation warrants. The practice should establish a relationship with a clinical pathologist before the need arises. The pathologist should be familiar with the practice and the types of cases that are seen. The pathologist should be available for consultation by phone or by email. The practice should also have a system for submitting the smears to the pathologist and for receiving the report. The World Organisation for Animal Health provides guidance on the welfare of animals in veterinary practice, including the importance of the humane handling of animals during diagnostic procedures. The use of the clinical pathologist is consistent with this guidance because it reduces the risk of misdiagnosis and the inappropriate treatment that can follow. ### The Role of the Practice Team The cytology service is not the responsibility of a single veterinarian. The entire practice team contributes to the quality of the cytology. The veterinary technician prepares the smears and the stains. The receptionist schedules the appointments and the follow up. The practice manager provides the resources and the training. The practice should have a written protocol for the cytology service that is followed by all members of the team. The protocol should include the collection technique, the preparation method, the staining schedule, and the triage system. The protocol should be reviewed on a regular basis and updated as needed. The practice should also provide the training for the new staff and the continuing education for the existing staff. The training should include the proper technique for the collection and the preparation of the samples. The training should also include the recognition of the common artifacts and the use of the triage system. The practice should have a culture that encourages the reporting of the errors and the discussion of the difficult cases. The team should feel comfortable asking for a second opinion and for the help of the clinical pathologist. The team should also feel comfortable to admit when a sample is not diagnostic and to repeat the sample. The World Small Animal Veterinary Association provides global guidelines for the clinical practice, including the importance of the diagnostic testing and the quality assurance. The practice that follows these guidelines is more likely to provide the accurate and the reliable cytology service. ### The Role of the Cytology in the Diagnostic Plan The cytology is one step in the diagnostic plan for the patient. The cytology is not the final answer. The cytology is a guide that helps the veterinarian to decide the next step. The next step may be a biopsy, a culture, or a treatment trial. The veterinarian should explain the role of the cytology to the owner. The owner should understand that the cytology is a preliminary test and that the histology may be needed for the final diagnosis. The owner should also understand the limitations of the cytology and the reasons for the follow-up tests. The American Veterinary Medical Association emphasizes that pet owners should work with their veterinarian to understand the purpose of the diagnostic tests and the meaning of the results. The veterinarian should take the time to explain the cytology result to the owner and to answer the questions. The owner should be involved in the decision about the next step. The cytology triage system is a practical tool that can be implemented in any practice. The system does not require the special equipment or the additional staff. The system requires the commitment to the quality and the willingness to follow the protocol. The system is a way to reduce the errors and to improve the patient care. ## Frequently Asked Questions ### What is the most common cause of a nondiagnostic cytology sample? The most common cause is a poor sample that contains too few cells or too much blood. The sample is often the result of a technique that is not correct, such as the use of a needle that is too small or the application of too much suction. The sample should be repeated with a technique that is correct. ### How can I tell the difference between stain precipitate and bacteria? Stain precipitate is often distributed evenly over the slide, while bacteria are associated with the cells or are present in a specific pattern. The precipitate is also not associated with the inflammatory response. If the precipitate is severe, the smear should be restained or the sample should be repeated. ### What is the difference between reactive mesothelial cells and malignant cells? Reactive mesothelial cells are enlarged and have a high nuclear to cytoplasmic ratio, but they are not malignant. The cells are present in response to inflammation or infection. Malignant cells are more uniform and may form clusters. The distinction is difficult, and the histology is often needed. ### When should I use a clinical pathologist for cytology? The clinical pathologist should be used when the cytology is ambiguous, when the diagnosis is uncertain, or when the cytology is the basis for a major decision. The pathologist has the training and experience to identify the cells and to provide a diagnosis. ### What is the role of histology in the diagnosis of a mass? Histology is the gold standard for the diagnosis of a mass. The histology examines the tissue architecture and the relationship between the cells. The histology is needed when the cytology is not diagnostic or when the cytology is not consistent with the clinical findings. ### How should I store the cytology slides? The slides should be stored in a dry, clean container. The slides should be labeled with the patient's name, the date, and the site of the labeling. The slides should be protected from moisture and direct sunlight. ### What is the best way to prepare a smear? The best way is to use a gentle, even pressure. The smear should be a monolayer of cells that are intact and not damaged. The smear should be air-dried and fixed according to the protocol. ### What should I do if the cytology is not consistent with the clinical findings? The cytology should be repeated, and the sample should be reviewed by a clinical pathologist. If the cytology is still not consistent, the histology should be performed. The clinical findings should be the basis for the decision, and the cytology should be used as a guide. ## Related Veterinary Guides - [Common Horse Feeding Mistakes to Avoid](/knowledge/veterinary-medicine/equine-care/horse-feeding-mistakes) - [Veterinary Toxicology: Common Toxins and Emergency Management](/knowledge/veterinary-medicine/emergency-critical-care/veterinary-toxicology-common-toxins-emergency-management) - [Cytology of the Respiratory Tract: Collection and Interpretation](/knowledge/veterinary-medicine/clinical-pathology/cytology-respiratory-tract-veterinary) - [Common Diagnostic Errors in NAVLE Preparation and How to Avoid Them](/knowledge/veterinary-medicine/navle-exam-prep/common-diagnostic-errors-in-navle-preparation-and-how-to-avoid-them) - [IACUC Protocol Review: Common Pitfalls and How to Avoid Them](/knowledge/veterinary-medicine/laboratory-animal-science/iacuc-protocol-review-common-pitfalls-and-how-to-avoid-them) ## 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. - [Rodent immunohistochemistry: pitfalls and troubleshooting.](https://pubmed.ncbi.nlm.nih.gov/24078006). Veterinary pathology, 2014. - [Common laboratory artifacts caused by inappropriate sample collection and transport: how to get the most out of a sample.](https://pubmed.ncbi.nlm.nih.gov/21596350). Topics in companion animal medicine, 2011. - [Glutaraldehyde - A Subtle Tool in the Investigation of Healthy and Pathologic Red Blood Cells.](https://pubmed.ncbi.nlm.nih.gov/31139090). Frontiers in physiology, 2019. - [Evaluation of the CytoRich technique for cervical smears.](https://pubmed.ncbi.nlm.nih.gov/9523146). Diagnostic cytopathology, 1998. - [[Microscopic diagnosis of tick-borne diseases in Maghreb].](https://pubmed.ncbi.nlm.nih.gov/16929764). Archives de l'Institut Pasteur de Tunis, 2004. > This article is educational and is not a substitute for veterinary diagnosis or treatment. Contact a veterinarian for advice about an individual animal.