Melissa Kaplan's
Herp Care Collection
Last updated January 1, 2014

Abnormal Lab Values in Reptiles

Abnormal CPK, red and white cell counts, phosphorous, total protein and other analytes may not signal illness in reptiles

© 2002 Melissa Kaplan

Note: the "norms" and other problems discussed below for apply to other animals, including humans.

Lab values are difficult to compare. Not only might they differ from country to country, but from lab to lab. For example, U.S. laboratories measure calcium as "mg/dl" (milligrams per deciliter) while European labs measure calcium as "mmol/l" (millimoles per liter).

In addition, the "norms"--normal ranges--that appear next to your reptile's test result are not necessarily numbers established by the testing of thousands of healthy reptiles of every known species, or even of species kept as pets. "Norms" are simply the range between highest and lowest values that lab has seen, minus the extremes at both ends (generally a 2.5 standard deviation). The "norm" may be based on 10 lizards, or 5 lizards, 3 tortoises and 6 snakes. Since the lab doesn't necessarily know if those animals were healthy when they were tested, the norm is, essentially meaningless.

A graphic example, one which anyone who suffers from thyroid disease, is the range for the various thyroid hormones. The "norm" for thyroid stimulating hormone (TSH) is 0.4-6. You may feel great when your level is 0.9-1, and lousy when it goes over 2. But all too many doctors decide, based solely on the test results and not on what the patient reports or exhibits, that their thyroid is fine simply because the patient's test result is within the "norm". It is this attitude that has caused undiagnosed and misdiagnosed thyroid disease to be among the top five misdiagnosed health problems in women in the United States. It can also be a problem in any situation where the patient is ignored and attention paid only to a piece of paper.

Because different labs have different "norms", comparing your snake's lab results to the results obtained by other snake owners will be meaningless if they weren't done by the same lab...and we already know that all norms are basically meaningless.

So, why does your vet order lab tests? Just as with a good physician, a good vet uses information obtained from careful examination and observation of the patient, information from careful questioning of the client, and compares that with the test results. Years of comparing the actual findings from the physical examination and what the client reports on behaviors, signs, etc., with the data on the laboratory's report on the serology and other tests completed, an experienced reptile vet will know that, despite what the lab's "norms" are, in the vet's own experience, the signs, exam findings plus lab results indicate a condition or possible range of conditions that can then be further narrowed down and treatment initiated.

Because far fewer animals go into making up reptilian "norms" than have dogs in dog "norms", cats in "cat" norms, etc., one of the reasons for taking your reptiles to a reptile vet is that they will have far more experience assessing reptilian patients and their reptilian lab test results than vets who only rarely see reptiles.

So, lab tests provide information useful in making a diagnosis or in determining what other diagnostic work needs to be done and what type of interim treatment, environmental changes, etc., need to be done before a final diagnosis can be made.

The following are some of the things that may lead to abnormal test results or, when the patient's values are out of range (outside of the "norm") may not actually be indicative of illness.

Lysing
I learned about the effects of lysis on lab results back when I was taking veterinary clinical nursing. Lysis plays a role in many abnormal lab result in iguanas and other reptiles who otherwise appear to be healthy, both by observation and the rest of the lab results, so it puzzles me why more vets don't think of this common mechanical (blood collection and transfer techniques) and stress-related problem when evaluating results.

Mechanical Lysing
When blood is forced through too small a needle, or passes at too high a speed in either direction through a needle, cell membranes are ruptured (lyse). Elevated blood pressure, or blood transferred too quickly from collection syringe into a tube, can also cause blood cells to lyse, as can freezing. Lysing can cause abnormal phosphorous, potassium, total protein (TP, buffy coat), and aspartate aminotransferase (AST) results. Abnormal protein can indicate kidney disease; it may also be elevated when the patient is dehydrated. AST is an enzyme found in liver, heart and skeletal muscle; while not a specific indicator of liver disease, it is used to monitor liver disease.

Stress and Disease-Related Lysing
If your otherwise healthy reptile is highly stressed just from being at the vet, or from being restrained in the position he is put in for the vet or tech to draw blood, that stress can elevate the blood pressure high enough to cause lysing. If the vet or tech is struggling to get the blood sample, resulting in prolonged restraining and/or multiple sticks, even if the reptile was calm to start with, the blood pressure is going to become elevated.

Disease, such as autoimmune hemolytic anemia, and toxic exposures (especially to petroleum products) can weaken cell membranes. This renders them more fragile and so susceptible to mechanical lysing. They may develop small perforations, permitting the slow leakage of cellular fluids, including electrolytes. Both will result in abnormal lab values.

Clotting
Reptile blood clots easily; the smaller the blood sample collected, the faster the sample will clot. If whole blood is needed for a specific test (such as a complete blood count (CBC)), it needs to be collected in or quickly transferred to a tube that contains an anticoagulant.

Most tests require plasma, the clear part that separates out after whole blood is spun in a centrifuge. Blood collected for such tests needs to be collected in tubes that do not contain any anticoagulant. Right after collection, the tubes must be spun right away, with the plasma siphoned off and transferred to an appropriate tube for handling and/or shipping.

As reptiles don't have the nice big, relatively easy-to-visualize blood vessels and veins that dogs and cats do, it can take longer to actually find the blood in reptiles, let alone get enough of it for testing. As the reptile's blood pressure goes up, so does that of the vet or technician doing the stick and the person holding the reptile, if there is one. All this serves as a negative feedback loop, with the stress going back and forth and getting more elevated the longer the process takes. Some vets or techs, anticipating a prolonged collection period, may lace the needle with heparin to prevent the blood from clotting while a large enough sample if obtained. This can affect the later test results, depending on how much heparin is used; it can also affect how the cells respond to staining.

Microtainers™ and Vacutainer™ Microhematocrit Tubes
Microtainers are the tubes with the colorful rubber tops used to store and transfer blood. The different color rubber stoppers indicate what, if any, chemical is in the tube. EDTA, a commonly used anticoagulant that comes already loaded into microtainers, lyses reptilian red blood cells. It has a chelating effect on some blood analytes and so results in inaccurately high potassium and low calcium test results. Microtainers containing heparin are better choices for reptiles but can still lead to later problems in staining or diluting the sample to the point of resulting in abnormal test values.

Microhematocrit tubes are the thin glass tubes used to obtain a very small blood sample directly from a finger stick (or a claw intentionally cut too short so as to bisect the blood vessel and obtain blood for a small sample) or other stick point site. These open-ended tubes are then plugged at both ends with a special clay, and then centrifuged. Some microhematocrit tubes come preloaded with heparin and so could lead to inaccurate information, including total protein (buffy coat).

What Goes Around Comes Around (Or Doesn't)
If whole blood or centrifuged samples are left sitting to long, the red blood cells (RBC) will continue to use the glucose in the blood. Once the plasma is removed and tested, the results for serum glucose will be abnormally low due to the RBCs activity. Serum potassium and phosphorous will increase in whole blood that hasn't been centrifuged soon after collection, especially if the RBCs have been damaged or weakened. Electrolytes, especially potassium and phosphorous, leak out of broken cells, throwing off other lab values.

Plasma
If the plasma isn't harvested carefully from the spun tubes, cells may be transferred into the new tube with the harvested plasma. As these cells break down and leak, the contents, including electrolytes and other analytes to become mixed in with the plasma, distorting the results. Ideally, whole blood should only be sent to the lab for tests requiring whole blood (such as a complete blood count, or CBC). Tests requiring only plasma should have carefully harvested plasma. To prevent further mechanical lysing, all tubes should be carefully packed to cushion them during shipment to the laboratory.

Elevated Creatine Phosphokinase (CPK)
This is sometimes called creatine kinase (CK). Is used in the diagnosis and monitoring of liver, kidney and heart disease. It is found in cardiac, smooth and skeletal muscle. It is easily elevated in times of stress, so just being and the vet, restrained and being stuck with a needle is enough to elevate, often significantly so, this enzyme. In the absence of any other indicators for liver, kidney or heart disease, an elevated CPK can be ignored.

Lipemia
While not common in reptiles, an elevated serum fat level can cause RBC lysing as well as causing abnormally elevated AST, calcium and uric acid.

Calcium
In some cases, metabolic bone disease may be present when there is an otherwise normal calcium:phosphorous ratio if the bone is able to supply enough calcium to keep the serum calcium and calcium:phosphorous ratio within "normal" range. To diagnose metabolic bone disease, one must also look to see what other signs are visible, such as tremors, swellings, etc. Too much calcium (hypercalcemia) is rare in reptiles. When present in anything other than a gravid female, the cause needs to be identified and corrected.

Using Claws for Blood Sampling
As more information is available throughout the exotic veterinary literature and conferences on reptile anatomy and lab collection techniques, using blood from claws has really become outdated. Blood collected from the claws can also confound the test results due to the presence of debris from the claw cutting and lysed cells, and the uric acid concentration may be elevated.

"It is difficult enough to interpret blood results in species in which we know so little about their physiology without complicating the process with poor clinical pathology techniques. Improving venipuncture techniques, proper sample handling, and the use of the correct collection materials are all important to getting the more realistic test results. The last step of proper interpretation is to use a laboratory or have an in-house laboratory that routinely processes these unique samples so your results are reliable and repeatable."

- Douglas R Mader DVM and Karen Rosenthal DVM

In case you want to know...
Lavendar and navy top tubes contain EDTA; green and green/gray top tubes contain heparin. Red top tubes contain nothing; yellow tops contain an inert gel.

Sources:

KG Benson DVM, J Paul-Murphy DVM, P MacWilliams DVM. Effects of hemolysis on plasma electrolyte and chemistry values in the common green iguana (Iguana iguana). Journal of Zoo and Wildlife Medicine 30(3):413-415

DR Mader DVM, K Rosenthal DVM. Laboratory Sampling in Reptile Patients: Do's and Don'ts. 1998 Proceedings, Association of Reptilian and Amphibian Veterinarians, pp. 55-57

Becton, Dickinson and Company

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Effects of hemolysis on plasma electrolyte and chemistry values in the common green iguana

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