INTERPRETING LAB TEST RESULTS ON RABBITS

by Lucile Moore

Understanding those emailed or printed results we get after our rabbit’s lab test can be difficult. I hope that the following explanations of two commonly‐ordered tests will help readers interpret their rabbit’s test results.

Printed results of the tests may be presented in graphical or numerical form. They usually include the test name and/or abbreviation, results, and the low and high ends of the normal range for that test. Results that fall outside the normal range may be noted in some way. It is important to compare the results to the range provided by the laboratory rather than ranges published in texts or online as different methodologies used for the test will result in slightly different ranges.

Rarely, errors in taking, handling or analyzing the sample will cause erroneous results, particularly if the sample is not stored correctly or is not analyzed soon enough after taking it. If you have concerns about the validity of a test result discuss it with your vet. In some cases a new test may be warranted.

Haematology.

In a CBC, or complete blood cell count, the amounts of the different kinds of blood cells present are tested.

Red blood cell (RBC or erythrocyte) count: Male rabbits and older rabbits tend to have higher counts than female and younger rabbits. Dehydration and stress from cold temperatures can cause high RBC counts. High counts of nucleated RBCs can be a sign of a bacterial infection; a very high count of nucleated RBCs can be a sign of a bad flea infestation or internal bleeding.

Slightly elevated counts of nucleated RBCs are not an abnormal finding in rabbits. The HCT (Hct, haematocrit) is a test in which the percent of red blood cells is calculated. A low value may be a sign of anemia. Hb, or hemoglobin concentration, can be used to help diagnose anaemia (low Hb) and its origin. Female rabbits tend to have much lower HB and Hct than males. Rabbits that get a lot of exercise may have elevated RBC, HB, and Hct values.

Platelets: High counts may be associated with iron‐deficiency anaemia and chronic bleeding. Cold stress can also cause elevated platelet values, as may drugs such as glucocorticoids and epinephrine. Low levels may be a sign of a severe allergic reaction, massive bleeding, aplastic anaemia, and systemic bacterial or fungal infections. Low values can also be caused by storing the sample for too long before it is analyzed.

White blood cells (WBC, leukocytes): White blood cell counts vary depending upon the age,  sex, breed and season of the year. WBC counts may include counts for specific types, such as monocytes, lymphocytes, neutrophils/heterophils and basophils. In rabbits it is often the proportion of the differing kinds rather than the total WBC count that helps determine the presence of an infectious disease. The proportion of neutrophils to lymphocytes should be 1:1; in a rabbit with an acute infection the proportion will often be nearer 2:1. A high value for monocytes can be a sign of chronic infection and a high value for eosinophils and/or basophils can be a sign of a parasitical infection.

Serum/blood chemistry. The focus on these tests is on parameters of blood other than cell counts.

Serum glucose: Although high glucose can be a sign of kidney disease, it is often caused by stress, including the stress of the trip to the vet and having blood drawn. High glucose values can also occur in rabbits with acute intestinal obstruction, hepatic lipidosis, hyperthermia, and shock. Some drugs can also cause elevated glucose levels, as can diabetes, but diabetes is extremely rare in rabbits. Low glucose levels can be caused by anorexia, digestive tract problems, liver disease, and septicaemia.

BUN (blood urea nitrogen): A key test used to assess kidney function. Urea levels depend upon a wide variety of factors, including the time of day, the amount of protein in the diet and how hydrated the rabbit is. Slightly high values are not uncommon in healthy rabbits. High values may indicate there is some kind of kidney disease. Elevated values can also be a sign of encephalitozoonosis (EC). Low levels may be caused by anabolic steroids or liver damage.

Rabbits on corticosteroids, tetracycline, or aminoglycosides may have elevated levels; rabbits on chloramphenicol can have either low or high levels.

 Creatinine: High values are often a sign of severe kidney or muscle damage. This test is less influenced by external factors than the BUN. However, levels may be high in rabbits that have gone a few hours without drinking water. A disadvantage of this test is that it does not show high levels until there has been substantial loss of kidney function (excepting temporarily high levels caused by dehydration, which do not involve such loss of function).

 Cholesterol and triglycerides: To obtain accurate values for cholesterol the animal must be fasting. Since it is unsafe to fast rabbits for more than a couple of hours, not to mention that it is essentially impossible to fast most rabbits because of consumption of cecotrophs, results from this test should be considered only in conjunction with other tests. High cholesterol values can be caused by obesity, a diet high in fats, pancreatitis and chronic kidney failure. Values also be high if the rabbit is not eating enough, but this is a sign of advanced hepatic lipidosis and has a poor prognosis. High triglyceride levels may be a sign of chronic kidney failure.

Calcium and phosphorus: Calcium levels are primarily influenced by the calcium content of the diet. High blood calcium levels in conjunction with clear urine (showing it is not being excreted as it should) are a sign of kidney failure. Low calcium levels are rare but can occur in rabbits with poor nutrition. High phosphorus levels can be a sign of chronic kidney failure or soft tissue trauma.

Serum protein: Total protein levels may be high in rabbits that are dehydrated, whether from gastrointestinal hypomotility (stasis) or other reasons. Low levels can be caused by malnutrition or liver disease. Low levels of albumin (a specific protein) can be a sign of a heavy infestation of parasites, and high levels are a sign of advanced liver disease.

Bilirubin: High serum bilirubin levels in young rabbits are often caused by hepatic coccidiosis; in older rabbits they are more likely to be caused by an obstruction of the bile duct by neoplasia (cancer) or an abscess.

AP (ALP, alkaline phosphatase): The normal range for this test is wide and varies with age (young rabbits have higher levels) and breed. A high value may be a sign of diseases affecting liver function such as hepatic coccidiosis, liver abscesses, and neoplasia.

 ALT (alanine aminotransferase), also called GPT and SGPT: Another test that helps the vet assess whether there has been any liver damage. Mildly high levels may be found in rabbits that appear healthy and it is thought they may be caused by low concentrations of toxins such as aflatoxins in food or compounds in wood‐based litters. High levels may be a sign of hepatic lipidosis or liver damage from hepatic coccidiosis.

AST (aspartate aminotransferase), formerly called SGOT: High values in conjunction with high ALT, AP, or protein may be a sign of liver damage. High levels may also be caused by the rabbit struggling during collection of the sample.

Urinalysis

The urinalysis is another lab test that is ordered fairly frequently. More so than in blood work the normal value is often “negative,” or the absence of the tested‐for compound.

 Protein: The normal finding is negative to trace amounts. High amounts can be a result of kidney damage/disease. High levels can also be caused by dehydration, strenuous exercise or stress, and for this reason protein is best looked at in conjunction with the specific gravity and the ratio of protein to creatinine. Dilute urine with a high protein value is more likely to be a sign of kidney damage/disease than concentrated urine with a similar protein value. Low protein levels can be a sign of malnutrition.

SG (specific gravity): An SG level at the lower end of the normal range when combined with high creatinine and BUN is a sign of poor kidney function.

pH: Normal rabbit urine has a high pH (7.5‐9). Lower pH can be caused by high‐protein diets, severe anorexia, and fever.

Glucose: The normal finding for glucose is negative, although trace amounts may be found in healthy rabbits. Higher amounts can be caused by stress, including pain or any experience which is frightening to the rabbit.

Ketones: The normal finding is negative. The presence of ketones indicates starvation or severe anorexia. Ketones may be seen in rabbits with severe dental disease that prevents them from eating or in rabbits on hay‐only diets that have severely impacted cecums. Rarely, ketones in the urine may be caused by diabetes mellitus.

Bilirubin: High levels of bilirubin in rabbit urine are unusual but elevated levels may be caused by poisoning from aflatoxins in contaminated food, hepatic coccidiosis, or neoplasia.

 Haematuria: Normally there is no blood present in rabbit urine. A positive result may be caused by inflammation and/or a urinary tract infection, crystals, or, less often, neoplasia.

Sediment: Calcium carbonate sediment is a normal finding in rabbit urine. Other crystals can be caused by drugs the rabbit is taking, and struvite crystals can be a sign of bacterial infection.

Urobilinogen: The finding for a healthy rabbit is negative. High levels may be caused by liver damage or drugs such as sulfonamides; low levels can be caused by long exposure to light.

Nitrate and nitrite: Urine normally contains nitrates, but some bacteria convert nitrate to nitrite. The normal result for nitrite is negative; a positive result is caused by bacteria in the urine. However, not all bacteria are able to convert nitrates to nitrite, so a negative result does not mean a UTI is not present.