# Insulin Assays in Veterinary Medicine ## Quick Answer - Insulin concentrations must always be interpreted alongside blood glucose to diagnose insulinoma, never as a standalone value. - The insulin-to-glucose ratio helps distinguish insulinoma from other causes of hypoglycemia in dogs and other species. - Sample handling errors, including hemolysis and delayed serum separation, can invalidate insulin measurements and lead to misdiagnosis. ## Understanding Insulin Assays in Veterinary Diagnostics Insulin assays measure the concentration of insulin in blood serum or plasma and serve as a cornerstone in the diagnostic workup of hypoglycemia in companion animals. The clinical value of an insulin measurement depends entirely on the glucose concentration at the time of sampling, because the two values must be interpreted as a paired set. A single insulin value without a corresponding glucose measurement provides little diagnostic information and can mislead the clinician. The primary clinical problem that insulin assays address is the differentiation of insulinoma, an insulin-secreting pancreatic beta-cell tumor, from other causes of hypoglycemia. In healthy animals, insulin secretion decreases when blood glucose falls. In animals with insulinoma, this regulatory mechanism fails, and insulin secretion continues despite low glucose. This inappropriate insulin secretion is the pathophysiologic basis for the diagnostic use of insulin assays. Veterinary clinicians use insulin assays in companion animals, primarily dogs and less commonly cats, when a patient presents with signs consistent with hypoglycemia. These signs include weakness, lethargy, collapse, seizures, and altered mentation. The diagnostic challenge is that many conditions can produce hypoglycemia, and the insulin assay helps narrow the differential list. The Merck Veterinary Manual provides authoritative background on endocrine disorders and diagnostic approaches in veterinary species, and clinicians should consult such sources for disease-specific guidance. The manual covers the clinical presentation and diagnostic testing for insulinoma and other pancreatic disorders. ## At a Glance | Diagnostic Element | What It Tells You | Clinical Decision Point | | --- | --- | --- | | Blood glucose | Confirms hypoglycemia | Glucose below reference range triggers insulin testing | | Serum insulin | Measures circulating insulin concentration | Interpreted only with paired glucose value | | Insulin-to-glucose ratio | Identifies inappropriate insulin secretion | Elevated ratio supports insulinoma diagnosis | | Fructosamine | Not used for insulinoma | Useful for diabetes monitoring, not hypoglycemia workup | The table above summarizes the core laboratory values used in the insulinoma diagnostic pathway. The glucose measurement comes first, and the insulin measurement follows only when hypoglycemia is confirmed. The ratio calculation provides the interpretive framework that distinguishes appropriate from inappropriate insulin secretion. ## Core Principles of Insulin Physiology Insulin is a peptide hormone produced by the beta cells of the pancreatic islets. Its primary function is to regulate glucose homeostasis by promoting cellular glucose uptake and storage. In healthy animals, insulin secretion is tightly coupled to blood glucose concentration. When glucose rises after a meal, insulin secretion increases. When glucose falls, insulin secretion decreases. This glucose-insulin feedback loop is the physiologic basis for interpreting insulin assays. The diagnostic question in suspected insulinoma is whether insulin secretion is appropriately suppressed in the face of hypoglycemia. In a healthy animal with blood glucose of 40 mg/dL, insulin should be low or undetectable. In an animal with insulinoma, insulin remains elevated despite the low glucose. The insulin-to-glucose ratio is a calculated value that expresses this relationship. Several formulas exist, including the insulin-glucose ratio and the amended insulin-glucose ratio. The amended ratio accounts for the fact that insulin should approach zero as glucose approaches zero, and it provides a more sensitive index of inappropriate insulin secretion. Clinicians should understand that insulin concentrations are reported in different units depending on the laboratory. Common units include uIU/mL and pmol/L. The conversion factor is 1 uIU/mL equals 6.945 pmol/L. Using the wrong unit in a ratio calculation produces an incorrect result and can lead to a false diagnosis. ## Sample Handling and Preanalytical Variables The accuracy of an insulin assay depends heavily on sample handling. Insulin is a peptide hormone that degrades over time, and red blood cells continue to metabolize glucose after collection. This ongoing glucose metabolism can lower the measured glucose concentration, creating a falsely low glucose value that does not reflect the animal's true status. Hemolysis is a common problem in veterinary blood samples. Red blood cell rupture releases enzymes that degrade insulin, leading to falsely low insulin concentrations. A hemolyzed sample can produce an insulin result that is artificially low, potentially causing a false-negative diagnosis in an animal that actually has insulinoma. The timing of sample collection is also critical. The insulin and glucose should be measured from the same blood sample, collected at the same time. Collecting glucose at one time and insulin at another time breaks the paired relationship and makes the ratio calculation invalid. Sample handling recommendations include the following: - Collect blood into a serum separator tube or plain red-top tube - Allow the sample to clot for 30 minutes at room temperature - Centrifuge the sample promptly to separate serum from cells - Remove the serum from the clot within 30 to 60 minutes of collection - Refrigerate the serum if the assay will be performed within 24 hours - Freeze the serum if the assay will be delayed beyond 24 hours The Cornell University College of Veterinary Medicine provides educational resources on sample handling and diagnostic testing for veterinary practitioners. Their guidance emphasizes the importance of proper sample collection and processing to ensure accurate laboratory results. ## The Diagnostic Workflow for Suspected Insulinoma The diagnostic approach to suspected insulinoma follows a structured sequence. The first step is to confirm hypoglycemia. A blood glucose below the reference range, typically below 60 to 70 mg/dL in dogs, establishes the clinical problem. The clinician should repeat the glucose measurement to confirm the finding and rule out laboratory error. The second step is to measure serum insulin in the same sample. The insulin concentration is then interpreted in the context of the glucose value. The key question is whether the insulin is appropriately suppressed for the degree of hypoglycemia. The third step is to calculate the insulin-to-glucose ratio. The amended insulin-to-glucose ratio is calculated as follows: insulin in uIU/mL divided by glucose in mg/dL minus 30. A ratio above a laboratory-specific threshold supports the diagnosis of insulinoma. The fourth step is to consider other causes of hypoglycemia. The differential list includes sepsis, hepatic insufficiency, hypoadrenocorticism, and exogenous insulin overdose. The insulin assay helps distinguish insulinoma from these other causes because insulinoma produces inappropriately high insulin while the other causes produce appropriately low insulin. The fifth step is to pursue diagnostic imaging to localize the tumor. Abdominal ultrasound is the most commonly used imaging modality, but it has limited sensitivity for small tumors. Advanced imaging such as computed tomography may be recommended by a veterinary specialist. The Merck Veterinary Manual provides guidance on the diagnostic approach to hypoglycemia and insulinoma in dogs and cats. The manual describes the clinical signs, diagnostic tests, and treatment options for this condition. ## Practical Workflow for Insulin Testing The following workflow outlines the practical steps for the clinician when a patient presents with signs consistent with hypoglycemia. 1. Measure blood glucose immediately using a point-of-care glucometer or laboratory analyzer 2. Confirm the low glucose with a second measurement if the first is below the reference range 3. Collect a serum sample for insulin measurement at the same time as the glucose measurement 4. Handle the sample according to the laboratory requirements for insulin testing 5. Submit the sample to a veterinary reference laboratory with the paired glucose value 6. Calculate the insulin-to-glucose ratio when the results return 7. Interpret the ratio in the context of the patient's clinical signs and other laboratory findings 8. Discuss the results with the owner and recommend further diagnostic steps if insulinoma is suspected The workflow requires coordination between the clinical team and the laboratory. The clinician must ensure that the laboratory receives the paired glucose value with the insulin sample, because the laboratory cannot interpret the insulin without the glucose. ## Options and Tradeoffs in Insulin Testing Several options exist for insulin testing in veterinary medicine, and each has advantages and limitations. The first option is the use of a reference laboratory for insulin measurement. This is the most common approach and provides the most reliable results. The trade-off is the delay between sample collection and result availability, which can be several days. The second option is the use of an in-house analyzer for insulin measurement. Some veterinary practices have point-of-care analyzers that can measure insulin. The tradeoff is that these analyzers may have different reference ranges and may be less accurate than reference laboratory methods. The third option is the use of a fructosamine measurement. Fructosamine is a glycated protein that reflects the average glucose concentration over the preceding two to three weeks. It is not used for insulinoma diagnosis but is used for monitoring diabetic control. The tradeoff is that fructosamine does not provide information about insulin secretion. The fourth option is the use of a glucose tolerance test. This test involves administering glucose and measuring the glucose and insulin response over time. It is not commonly used for insulinoma diagnosis because the insulin-to-glucose ratio is simpler and more direct. The choice of testing approach depends on the clinical situation, the availability of laboratory services, and the cost to the owner. The clinician should discuss the options with the owner and select the approach that provides the most diagnostic information for the clinical question. ## Observations and Measurements in Insulinoma Cases The clinical observations and measurements in insulinoma cases follow a predictable pattern. The patient typically presents with signs of neuroglycopenia, which are the neurologic signs caused by low glucose in the brain. These signs include weakness, lethargy, ataxia, collapse, seizures, and altered mentation. The physical examination may be unremarkable between episodes of hypoglycemia. The clinician should obtain a thorough history, including the timing of signs relative to meals and exercise. Signs that occur after fasting or after exercise are more consistent with insulinoma. The laboratory measurements in insulinoma cases include the following: - Blood glucose is low, typically below 40 to 70 mg/dL - Serum insulin is elevated or inappropriately normal for the glucose - The insulin-to-glucose ratio is elevated - Other laboratory values are typically normal The clinician should also measure other parameters to rule out other causes of hypoglycemia. These include liver enzymes, cortisol, and electrolytes. The liver enzymes help rule out hepatic insufficiency, and the cortisol helps rule out hypoadrenalyticism. The World Organisation for Animal Health provides official guidance on animal health and welfare, and the clinician should consider the welfare implications of the diagnostic workup. The diagnostic tests are minimally invasive and the welfare impact is low, but the clinician should still consider the patient's comfort and the owner's concerns. ## Records and Documentation for Insulin Testing The clinician should maintain accurate records of the insulin testing process. The records should include the following information: - The date and time of sample collection - The patient's signalment and clinical signs - The blood glucose value at the time of collection - The serum insulin value - The insulin-to-glucose ratio - The laboratory that performed the assay - The reference ranges for the laboratory - The interpretation of the results - The follow-up plan The records serve several purposes. They provide a baseline for monitoring the patient's response to treatment. They document the diagnostic process for the medical record. They allow the clinician to review the case if the patient's condition changes. The records should be maintained in the patient's medical record and should be available to the owner upon request. The owner should be informed of the results and the implications for the patient's care. ## Common Failure Patterns in Insulin Testing Several common failure patterns can compromise the accuracy of insulin testing and lead to diagnostic errors. The first failure pattern is collecting the insulin sample without a paired glucose value. This is the most common error. The insulin result is uninterpretable without the glucose, and the sample is wasted. The second failure pattern is using the wrong units in the ratio calculation. The insulin-to-glucose ratio requires insulin in uIU/mL and glucose in mg/dL. Using pmol/L for insulin or mmol/L for glucose produces an incorrect ratio. The third failure pattern is delayed sample processing. The insulin degrades over time, and the glucose continues to be metabolized by red blood cells. A sample that is not processed promptly produces falsely low values for both insulin and glucose. The fourth failure pattern is interpreting the insulin value without considering the clinical context. A single insulin value above the reference range does not confirm insulinoma. The value must be interpreted in the context of the glucose and the clinical signs. The fifth failure pattern is failing to consider other causes of hypoglycemia. The insulin assay is a diagnostic tool, not a diagnosis. The clinician must consider the full differential list and pursue the appropriate diagnostic tests. The sixth failure pattern is failing to repeat the measurement when the result is borderline. A borderline insulin-to-glucose ratio should be repeated to confirm the result before proceeding with invasive diagnostic tests. ## Limitations of Insulin Assays Insulin assays have several limitations that the clinician should understand. The first limitation is the lack of a standardized reference range across laboratories. Different laboratories use different assay methods and report different reference ranges. The clinician must use the reference range provided by the laboratory that performed the assay. The second limitation is the cross-reactivity of the assay with other insulin-like molecules. Some assays cross-react with proinsulin and other insulin precursors, which can produce a falsely elevated insulin result. The third limitation is the effect of the patient's body condition on insulin. Obese animals have higher baseline insulin concentrations, which can affect the interpretation of the ratio. The fourth limitation is the effect of concurrent disease on insulin. Animals with other endocrine diseases, such as hypothyroidism or hyperadrenalyticism, may have altered insulin concentrations. The fifth limitation is the effect of medications on insulin. Some medications, such as corticosteroids, can increase insulin resistance and alter insulin concentrations. The clinician should consider these limitations when interpreting the insulin result and should use the result in the context of the full clinical picture. ## Safety and Welfare Considerations The diagnostic workup for insulinoma involves minimal risk to the patient. The blood collection is a routine procedure that is well tolerated by most animals. The clinician should use appropriate restraint and aseptic technique to minimize the risk of complications. The welfare of the patient should be a primary consideration throughout the diagnostic process. The clinician should minimize the number of blood collections and should use the smallest volume of blood needed for the tests. The clinician should also consider the stress of the diagnostic process on the patient and the owner. The World Veterinary Organization provides official guidance on animal health and welfare, and the clinician should follow this guidance in the diagnostic process. The welfare of the patient should be balanced against the need for an accurate diagnosis. The American Veterinary Medical Association provides resources for pet owners on preventive care and the importance of regular veterinary visits. The clinician should use these resources to educate the owner about the importance of the diagnostic workup and the treatment plan. ## Professional Escalation Criteria The clinician should escalate the case to a veterinary specialist in the following situations: - The insulin-to-glucose ratio is elevated and the diagnosis of insulinoma is suspected - The patient has recurrent hypoglycemia despite treatment - The patient has a suspected insulinoma that requires surgical removal - The patient has a complex endocrine disease that requires specialist management - The patient has a poor response to initial treatment The specialist may be a veterinary internal medicine specialist or a veterinary surgeon. The specialist can provide advanced diagnostic imaging, surgical treatment, and ongoing management of the condition. The clinician should also escalate the case if the laboratory results are inconsistent with the clinical picture. The clinician should repeat the testing and consider the possibility of a laboratory error. ## A Decision Framework for Borderline Insulin-to-Glucose Ratios The interpretation of insulin assays becomes most challenging when the insulin-to-glucose ratio falls into a borderline zone instead of a clearly elevated or clearly normal range. In these cases, the clinician must decide whether to pursue invasive diagnostic testing, repeat the laboratory work, or monitor the patient over time. A structured decision framework helps the clinician avoid both unnecessary procedures and delayed diagnoses. ### Defining the Borderline Zone The borderline zone is not a fixed set of numbers because reference ranges vary between laboratories and assay methods. The clinician should first identify the laboratory-specific threshold for an elevated amended insulin-to-glucose ratio. The borderline zone typically sits between the upper limit of normal and approximately 20 percent above that threshold. For example, if a laboratory reports an amended insulin-to-glucose ratio above 30 as consistent with insulinoma, the borderline zone would be roughly 30 to 36. The clinician should confirm the exact threshold with the performing laboratory before applying this framework. The borderline zone also includes situations where the insulin concentration is within the reference range but the glucose is low. In a healthy animal, insulin should be suppressed when glucose falls below the reference range. A normal insulin value in the face of hypoglycemia is not a normal result. It represents an inappropriate lack of suppression and should be treated as a borderline finding instead of a negative result. The third situation that falls into the borderline zone is when the glucose and insulin values are collected at different times. This breaks the paired relationship and makes the ratio calculation invalid. The clinician should treat this as an uninterpretable result and repeat the sampling instead of attempting to interpret the ratio. ### The Three-Pass Decision Framework The framework uses three passes through the available data. Each pass asks a different question and narrows the clinical options. The clinician should complete all three passes before making a recommendation to the owner. #### Pass One: Verify the Sample The first pass asks whether the laboratory values are trustworthy. The clinician reviews the sample handling record and the laboratory report for the following items: - The glucose and insulin were measured from the same blood sample - The sample was collected in a serum separator tube or plain red-top tube - The sample was allowed to clot for 30 minutes at room temperature - The serum was separated within 30 to 60 minutes of collection - The sample was refrigerated or frozen according to laboratory requirements - The sample was not visibly hemolyzed or lipemic - The laboratory reported both glucose and insulin on the same accession If any of these items are missing or questionable, the clinician should repeat the sampling before proceeding. A single questionable sample should not drive an invasive diagnostic plan. The clinician should also verify that the units on the laboratory report match the units used in the ratio calculation. Insulin is commonly reported in uIU/mL or pmol/L, and glucose is reported in mg/dL or mmol/L. The conversion factor for insulin is 1 uIU/mL equals 6.945 pmol/L. Using the wrong units produces a ratio that is incorrect by a factor of approximately seven, which can shift a clearly elevated result into the normal range or vice versa. **Pass Two: Assess the Clinical Context** The second pass asks whether the laboratory values fit the patient's clinical picture. The clinician reviews the history and physical examination findings for consistency with neuroglycopenia. The signs of neuroglycopenia include weakness, lethargy, ataxia, collapse, seizures, and altered mentation. These signs should occur in relation to fasting or exercise and should resolve with feeding. The clinician should ask the owner about the timing of signs relative to meals, the duration of signs, and the response to feeding. The physical examination should include a careful assessment of mentation and neurologic function. The clinician should also examine the patient for other causes of hypoglycemia, including hepatic disease, hypoadrenalyticism, and sepsis. The clinician should review the minimum database, including liver enzymes, cortisol, and electrolytes, to rule out these other causes. The clinical context helps the clinician decide whether the borderline ratio is likely to represent insulinoma or an artifact. A patient with classic signs of neuroglycemia and a borderline ratio is more likely to have insulinoma than a patient with no clinical signs and a borderline ratio. The clinician should weigh the clinical context heavily in the decision. **Pass Three: Determine the Next Step** The third pass uses the results of the first two passes to select the next step. The options are repeat testing, additional diagnostics, or referral. The clinician should repeat the insulin and glucose measurement when the sample quality is questionable, when the clinical signs do not match the laboratory values, or when the ratio is borderline and the patient has no clinical signs. The repeat sample should be collected under the same conditions as the first sample, ideally after a 12-hour fast. The clinician should compare the two sets of results to determine whether the borderline finding is reproducible. The clinician should pursue additional diagnostics when the ratio is borderline and the patient has clinical signs consistent with hypoglycemia. The additional diagnostics may include a fasting trial under hospital observation, serial glucose measurements, or diagnostic imaging. The fasting trial involves withholding food for 6 to 12 hours and measuring glucose at intervals. The clinician should monitor the patient closely during the fast and be prepared to intervene if the glucose falls below a safe threshold. The clinician should refer to a specialist when the ratio is clearly elevated, when the patient has recurrent hypoglycemia despite treatment, or when the patient has a suspected insulinoma that requires surgical removal. The specialist can provide advanced imaging, surgical treatment, and ongoing management of the condition. ### A Record System for Serial Insulin Testing The borderline case often requires serial testing to establish a pattern. The clinician should maintain a structured record of each testing event to track the trend over time. The record should include the following fields for each event: - Date and time of sample collection - The patient's clinical signs at the time of collection - The blood glucose value - The serum insulin value - The insulin-to-glucose ratio - The laboratory and assay method - The sample quality indicators, including hemolysis and lipemia - The clinical decision made at that time The record should be maintained in the patient's medical record and reviewed at each visit. The clinician should look for a trend in the ratio over time. A ratio that is rising over serial measurements is more concerning than a ratio that is stable or falling. The record also serves as a communication tool for the owner. The owner can see the progression of the values and understand the clinical decision. The owner should be informed of the results at each step and the implications for the patient's care. ### Troubleshooting Common Borderline Scenarios The following scenarios describe common borderline presentations and the recommended approach for each. **Scenario One: Low Glucose and Normal Insulin** The patient has a glucose of 50 mg/dL and an insulin of 5 uIU/mL. The insulin is within the reference range, but the glucose is low. The amended insulin-to-glucose ratio is 5 divided by 50 minus 30, which equals 0.25. This is below the typical threshold of 0.3. The clinician should not interpret this as a negative result. The insulin should be suppressed in the face of hypoglycemia, and a normal insulin value represents inappropriate secretion. The clinician should repeat the testing and consider the clinical context. If the patient has signs of hypoglycemia, the clinician should pursue additional diagnostics. **Scenario Two: Borderline Ratio and No Clinical Signs** The patient has a glucose of 60 mg/dL and an insulin of 12 uIU/mL. The amended ratio is 12 divided by 60 minus 30, which equals 0.4. This is above the typical threshold of 0.3, but the patient has no clinical signs of hypoglycemia. The clinician should repeat the testing to confirm the result. The patient should be monitored for the development of clinical signs. The clinician should consider the possibility of a false positive result and should not proceed to invasive diagnostics based on a single borderline value. **Scenario Three: Borderline Ratio and Strong Clinical Signs** The patient has a glucose of 45 mg/dL and an insulin of 10 uIU/mL. The amended ratio is 10 divided by 45 minus 30, which equals 0.67. This is clearly elevated, and the patient has signs of neuroglycemia. The clinician should pursue the diagnosis of insulinoma and refer the patient to a specialist for further evaluation. The specialist can perform advanced imaging and plan the surgical treatment. **Scenario Four: Uninterpretable Sample** The glucose and insulin were collected at different times, or the sample was hemolyzed. The clinician should repeat the sampling before making any clinical decision. The repeat sample should be collected under the same conditions and handled according to the laboratory requirements. ### The Role of the Owner in the Decision Process The owner is a key participant in the decision process. The clinician should explain the borderline nature of the results and the need for repeat testing or additional diagnostics. The owner should understand that a single borderline result does not confirm the diagnosis and that the diagnostic process may take several days or weeks. The owner should be instructed to monitor the patient for signs of hypoglycemia and to provide food at regular intervals. The owner should also be instructed to seek immediate veterinary care if the patient develops severe signs such as collapse or seizures. The American Veterinary Medical Association provides resources for pet owners on preventive care and the importance of regular veterinary visits. The clinician should use these resources to educate the owner about the diagnostic process and the treatment plan. ### When to Stop Testing and Act The decision framework includes a clear point at which the clinician should stop repeating tests and act. This point is reached when the patient has a confirmed hypoglycemia, a consistently elevated insulin-to-glucose ratio, and clinical signs consistent with neuroglycemia. At this point, the clinician should refer the patient to a specialist for surgical evaluation. The clinician should also act when the patient has recurrent hypoglycemia despite a normal ratio. The recurrent hypoglycemia is a clinical problem that requires treatment regardless of the ratio. The clinician should consider other causes of hypoglycemia and pursue the appropriate diagnostics. The clinician should not delay the referral when the patient has a confirmed insulinoma. The surgical removal of the tumor is the treatment of choice, and the delay can allow the tumor to grow and the clinical signs to worsen. ### The Role of the Specialist in the Decision Process The specialist provides the advanced diagnostic and surgical expertise that the primary care clinician does not have. The specialist can perform advanced imaging such as computed tomography to localize the tumor. The specialist can also perform the surgical removal of the tumor and provide the postoperative management. The specialist should be involved early in the decision process when the patient has a confirmed insulinoma or a strong suspicion of the disease. The specialist can provide guidance on the diagnostic plan and the surgical approach. The World Small Animal Veterinary Association provides global guidelines for companion-animal clinical practice. The clinician should consult these guidelines for the current recommendations on the diagnosis and treatment of insulinoma. ### The Role of the Laboratory in the Decision Process The laboratory is a partner in the decision process. The clinician should contact the laboratory when the results are borderline or when the sample quality is questionable. The laboratory can provide information about the assay method, the reference range, and the sample handling requirements. The laboratory should also be informed of the clinical context when the result is borderline. The laboratory may be able to provide additional testing or to repeat the assay on the same sample. The clinician should maintain a working relationship with the laboratory to ensure the best possible diagnostic outcome. ### The Decision Framework in Practice The decision framework is a practical tool that the clinician can apply to each case of suspected insulinoma. The framework provides a structured approach to the interpretation of the insulin-to-glucose ratio and the clinical decision process. The framework is not a substitute for clinical judgment. The clinician should use the framework as a guide and should adapt the approach to the individual patient and the clinical situation. The framework should be used in the context of the full clinical picture, including the history, the physical examination, and the other laboratory findings. The framework is also a teaching tool for the owner. The clinician can use the framework to explain the diagnostic process and the reasons for the clinical decisions. The owner should understand the steps in the process and the expected timeline for the diagnosis and treatment. The decision framework is a practical approach to the borderline insulin-to-glucose ratio. The framework helps the clinician avoid the common failure patterns of overdiagnosis and underdiagnosis and provides a structured path to the correct clinical decision. ## Frequently Asked Questions ### What is the insulin-to-glucose ratio and why is it used? The insulin-to-glucose ratio is a calculated value that compares the serum insulin concentration to the blood glucose concentration. It is used to determine whether insulin secretion is appropriately suppressed in the face of low glucose. In insulinoma, the ratio is elevated because insulin remains high despite low glucose. ### How should a blood sample be handled for insulin testing? The blood sample should be collected in a serum tube and allowed to clot for 30 minutes. The sample should then be centrifuged and the serum removed within 30 to 60 minutes. The serum should be refrigerated if the assay is performed within 24 hours and frozen if the assay is delayed beyond 24 hours. ### What causes a falsely low insulin result? A falsely low insulin result can be caused by hemolysis, delayed sample processing, or prolonged storage of the sample. The red blood cells continue to metabolize insulin after collection, and hemolysis releases enzymes that degrade insulin. ### What causes a falsely elevated insulin result? A falsely elevated insulin result can be caused by cross-reactivity with proinsulin or other insulin-like peptides. The assay may also be affected by the patient's body condition, with obese patients having higher insulin concentrations. ### What other conditions can cause hypoglycemia in dogs and cats? Other causes of hypoglycemia include hepatic insufficiency, hypoadrenalyticism, sepsis, and exogenous insulin overdose. The insulin assay helps distinguish insulinoma from these other causes because insulinoma produces elevated insulin while the other causes produce appropriately low insulin. ### When should I refer a patient with suspected insulinoma to a specialist? The patient should be referred to a specialist when the diagnosis is confirmed, when the patient has recurrent hypoglycemia, or when surgical removal of the tumor is planned. The specialist can provide advanced imaging and surgical expertise. ### What is the difference between serum insulin and fructosamine? Serum insulin is a direct measurement of the insulin concentration at the time of collection. Fructosamine is a measure of the average glucose concentration over the preceding two to three weeks. Fructosamine is used for monitoring diabetic control, not for diagnosing insulinoma. ### How long does it take to get insulin results from a reference laboratory? The turnaround time for insulin results depends on the laboratory and the shipping time. Most reference laboratories provide results within two to five days of receiving the sample. The clinician should plan the diagnostic workup accordingly. --- ## 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 - [Clinical Reasoning in Veterinary Medicine: From Data Gathering to Diagnosis](/knowledge/veterinary-medicine/clinical-skills-training/clinical-reasoning-veterinary-medicine-data-gathering-diagnosis) - [Conducting Pharmacovigilance Studies in Veterinary Medicine](/knowledge/veterinary-medicine/veterinary-research-methods/conducting-pharmacovigilance-studies-veterinary-medicine) - [Measuring Agreement in Veterinary Diagnostic Tests](/knowledge/veterinary-medicine/veterinary-research-methods/measuring-agreement-veterinary-diagnostic-tests) - [Coagulation Testing in Veterinary Medicine: A Practical Guide](/knowledge/veterinary-medicine/clinical-pathology/coagulation-testing-veterinary-practical-guide) - [Feline Hypoglycemia: Causes, Diagnosis, and Management](/knowledge/veterinary-medicine/clinical-methods/feline-hypoglycemia-causes-diagnosis-management) ## 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. - [Retrospective study of 20 cats surgically treated for insulinoma.](https://pubmed.ncbi.nlm.nih.gov/36124622). Veterinary surgery : VS, 2023. - [Medical management of canine hyperinsulinism.](https://pubmed.ncbi.nlm.nih.gov/3894306). Journal of the American Veterinary Medical Association, 1985. - [Insulinoma in a ferret.](https://pubmed.ncbi.nlm.nih.gov/3021697). Journal of the American Veterinary Medical Association, 1986. - [[Insulinoma].](https://pubmed.ncbi.nlm.nih.gov/6290907). Nederlands tijdschrift voor geneeskunde, 1982. - [Evaluation of the expression of hexokinase 1, glucokinase, and insulin by canine insulinoma cells maintained in short-term culture.](https://pubmed.ncbi.nlm.nih.gov/33480281). American journal of veterinary research, 2021. > This article is educational and is not a substitute for veterinary diagnosis or treatment. Contact a veterinarian for advice about an individual animal.