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Reptilian clinical pathology (Proceedings)

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Apr 01, 2009

"Bad laboratory data are worse than no laboratory data at all." Considering the variety amongst our veterinary patients, I think that this old saying has the most significance in the practice of exotic animal medicine. There are certainly many clinical pathology laboratories around, and most of which do an outstanding job in veterinary laboratory analysis. But, just as is the case in the changing face of our profession, with every dog and cat practice now hanging out a shingle that claims expertise with exotics, almost all clinical laboratories are also claiming expertise in the non-domestic arena.

Especially with the birds and reptiles, animal groups claiming ownership of a unique leukocyte, called the heterophil, evaluation of the hemogram and differential can be very difficult, and requires substantial training and experience. As a case in point, take a single exotic blood sample, split it into five smears and send them to a small mammal laboratory. Two smears can be submitted on the first day, each with a different name, and the remaining three can each be submitted on subsequent days, also with different names. I can almost guarantee that you will have five different results!

Don't interpret this as arrogance on my part. I realize the difficulty of the task, and as a result, I always send my hematology samples to a trained exotic animal clinical pathologist. The morphology of the cells vary between animal groups (eg. birds - reptiles), and between species within a group (iguanas - chameleons). Unless the technician is thoroughly familiar with the normals for EACH species, there is no possible way they will be able to evaluate either normal or abnormal samples from clinical cases.

The laboratory that I use for my hematology samples has only one technician read ALL of the slides. This is very important since I know that when I am sending in serial samples, each subsequent slide is always being evaluated by the same individual. Many large commercial laboratories utilize the service of many technicians. There will inevitably be differences between their abilities. If you send in a sample and get a qualified technician you may get reliable results. However, you may also get one of the less experienced technicians (less experienced with non-domestic bloods), and the results may be worthless (or even potentially dangerous).

The most productive scenario is to either do all of your exotic hematology yourself, or have a trained and practiced technician do your lab work. A technician skilled at reading exotic hemograms is a valuable asset (and practically a necessity) in any non-domestic practice. There are a few books available on the subject, and for their price, are worth every penny.

Obtaining samples for hematology and clinical chemistry in reptiles can be a clinical challenge. Standard sampling techniques such as cardiocentesis, jugular, axillary, femoral, buccal and tail vein venipuncture can all be used. Each has its advantages and limitations, and with practice and experience each clinician will develop proficiency in the techniques that suits him or her best. Comprehensive descriptions of these techniques are beyond the scope of this paper, but accurate descriptions are available elsewhere.

Briefly, in snakes, either tail vein (especially in crotalids) or cardiocentesis are the best techniques for collecting blood. I routinely use cardiocentesis, and in twelve years and literally thousands of snakes, have never had a problem.

In lizards I prefer tail vein bleeding. Although, axillary is satisfactory in many cases. There is an increased chance of lymph contamination in the latter technique.

In chelonians either jugular vein bleeding, or collection of blood from either the axillary or femoral plexus can all be used. The former is the preferred method in gentle animals.

I do not encourage toe-nail bleeding. With all of the other convenient alternatives available I see no reason to take a perfectly normal tissue (the nail) and destroy it. Not only does this technique require more time, it yields a lymph contaminated sample and undoubtedly causes considerable pain to the patient. If you don't believe this, try clipping the tip of your finger off just under the nail bed!

Blood volumes in reptiles vary from five to eight percent of their total body weight. Of this amount, up to ten percent can be safely collected for analysis without harm to the patient. As a rough approximation, the sample size should never be larger than one percent of the animal's total body weight. For example, in a 450 g iguana, you can safely remove 4.5 cc's of blood. This is way more than required by even the most antiquated autoanalyzers.