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.
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.
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.
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.
and Vacutainer Microhematocrit Tubes
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).
Goes Around Comes Around (Or Doesn't)
Creatine Phosphokinase (CPK)
Claws for Blood Sampling
"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."
you want to know...
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
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