There can be many challenges when working with exotic pets. Venipuncture access and volume, cell identification and artifacts, finding a laboratory comfortable with exotic animals, and understanding the differences in disease pathology as it relates to clinical pathology can all be difficult when working with non-traditional pets.
Appendix one has a list of the best venipuncture sites by species along with the volume that can be obtained and some tips on blood collection.
Complete Blood Count
The CBC varies a lot between species especially in animals with nucleated red blood cells like birds and reptiles. In general, most animals have a white blood cell count of 5,000–15,000/uL. The exception to that would be mustelids which tend to have white blood cell counts that are a little lower and normally are 2000–10,000/uL. Likewise, if you work on any exotic hoof stock, they have lower white blood cell counts in that same range and similar to other ruminants.
Pack cell volume can vary also by species. The more oxygen and energy expended or needed by the species the higher or lower their PCV. Reptiles generally sit in the 15–30% range, mammals in the 30–50% range and birds in the 40–60% range.
Total protein concentrations in birds and reptiles are about half of mammalian concentrations in most cases. It is important to always look at the albumin/globulin ratio (A/G) since the total protein may remain normal while the A/G ratio is altered. The normal A/G is approximately 1.5–3.5.
Plasma electrophoresis (EPH) can also be helpful especially in avian patients, and some reptiles as well, although there can be laboratory and sample handling issues that affect the outcome of the test. It is important to always use the same lab when tracking EPH changes over time in a patient. It also is important to use plasma for the sample. The five main fractions of the electrophoresis are albumin, alpha-1, alpha-2, beta and gamma globulins. Some species like psittacines also have a pre-albumin fraction. In acute diseases, alpha-1 and alpha-2 proteins appear to elevate. The beta globulin portion consists of acute phase proteins including fibrinogen. The gamma globulins consist mainly of globulins. By interpreting the increases and decreases of the protein concentration, one can get an idea of whether an infection is present and if it is acute or chronic. For example, hyperbetaglobulinemia and hypergammaglobulinemia is common in infections of Chlamydophila and aspergillosis. When interpreting the EPH, the white blood cell count should also be considered since a mild increase in one of the fractions may be significant if the white blood cell count is elevated.
The chemistry panel can help locate areas of concern in the patient. There are tests that have limited value in birds and reptiles including alanine aminotransferase, alkaline phosphatase (ALP), bilirubin, and creatinine. For example, ALP is not present in the liver of birds and gamma glutamyltransferase (GGT) activity is low in the avian liver. Below are a few tests that can be helpful in exotic patients.
For birds and reptiles, uric acid is more helpful than BUN. While BUN is the end products of protein metabolism, for most animals, for birds and reptiles uric acid is the end product. In general, a fasted animal should have a low uric acid number that is less than 10 mg/dl. For aquatic turtles BUN is more common over uric acid.
Calcium levels are very important for reptiles and birds and should be maintained at a ratio of 2:1 of calcium: phosphorus. Calcium should always be evaluated in tandem with albumin. Metabolic bone disease is a common condition in pet reptiles due to inappropriate nutrition that requires close evaluation of calcium status. Likewise pregnancy, dystocia and chronic egg laying also require attention to calcium levels. Since total calcium is not an accurate representation of a patient's calcium, ionized calcium is often used instead. In general, ionized calcium over 1.0 mmol/L is considered adequate but each species has a specific number that is considered normal. For example, green iguanas are usually closer to 1.4 and some skink species are closer to 2.0. When evaluating calcium, vitamin D levels, phosphorus and parathyroid levels can also be helpful. Elevated calcium levels are a common finding in birds and reptiles that are going through follicular genesis. Cholesterol and albumin will also increase during these times.
Glucose values also vary by species. For small mammals, typical glucose is similar to domestic pets and is in the 70–150 mg/dl range. For reptiles, glucose can be lower in the 40–60 mg/dl range. For birds glucose is normally 150 mg/dl to 300 but levels of 600 can occur with stress.
In addition to the traditional CBC and chemistry, there are some additional tests that are useful in exotic species. For example, the adrenal panel looking at the sex hormone status in ferrets, vitamin D status in reptiles with nutritional deficiencies, iron panels for birds affected with hemochromatosis and iodine deficiencies in sharks to name a few. There are also artifacts to acknowledge such as lipemia in normal ovulating birds. Even if a clinician generally sends out blood for hemogram evaluation to a laboratory, it is important to be aware of cell differences in animals so that performing a quick in house slide review can be helpful. For example, the most common rabbit leukocyte is the heterophil and in some species of aquatic turtles, the basophil is the most prevalent leukocyte. There are a number of books, journals and web resources that can help in evaluating exotic clinical pathology and exotic pet disorders.
Appendix i. A Description of Common Venipuncture Sites by Species
Generally your best venipuncture site will be the right jugular. The left jugular is always smaller than the right and is very difficult to find and access. Other sites include the wing (basilica) veins but you have to be careful of hematomas and the median tarsometatarsal vein on the inside of the upper leg. Can obtain 10 ml/kg.
The best site in snakes is the midline ventral or lateral coccygeal vein. The lateral approach tends to flow better for larger volumes. If clear or diluted blood is obtained than lymph contamination has occurred and the sample needs to be discarded to avoid artifacts. Cardiocentesis in larger (more than 200 gram) snakes can also be performed by a ventral approach after identifying direct visualization of the heart beating. Make sure to isolate the heart between the index finger and thumb and have good restraint. Can obtain 5 ml/kg.
The midline ventral or lateral coccygeal vein can be used similar to snakes. The jugular vein can also be used. The jugular vein is a blind approach and is located from the tympanum area to the point of the shoulder and inserting the needle in at a 45 degree angle. The animal should be restrained in a lateral plane and the head flexed away from the venipuncture site. Can obtain 5 ml/kg.
There are several good sites including the subcarapacial venous sinus, the jugular vein, the brachial venous plexus, the femoral venous plexus and the femoral vein. The jugular vein is the best site for lymph-free samples. With the other sites, one must be observant for lymph contamination. Can obtain 5–8 ml/kg.
The best site for crocs and alligators is the ventral or lateral aspect of the ventral coccygeal vein. The other sites are the supravertebral sinus and a lateral occipital sinus vessel laterally. Can obtain 5–8 ml/kg.
Aquatic and Amphibian Species
For sharks the best venipuncture area is the lateral approach to the ventral coccygeal vein. For rays the ventral approach to the coccygeal vein is best. For most fish the caudal tail vein from a lateral or ventral approach can be used. For amphibians the ventral abdominal vein, as well as the saphenous and femoral veins can be used although I find the femoral easier to use. It is best to use gloves when collecting blood in aquatic and amphibian species to protect their skin layer and to protect yourself from sharp spines or scales. Can obtain 5–8 ml/kg.
Small mammals such as sugar gliders, hamsters, and guinea pigs can be difficult to obtain blood from. The most successful sites are the femoral vein and tail vein. For the femoral vein, carefully shave the area to visualize the vessel and then use a tuberculin syringe. For the tail vein the approach is similar to that in snakes and other reptiles. Can obtain 10 ml/kg for all small mammals.
For ferrets the jugular, cranial vena cava, femoral and tail vein can be used. For the cranial vena cava good restraint is needed if done awake. I find it is generally a three person job, with one person restraining, one person offering oral dextrose via syringe to the animal and one person collecting blood.
Venipuncture sites in rabbits include the jugular vein, the femoral vein and the lateral saphenous vein. I find the lateral saphenous the easiest to obtain blood from. Carefully shave the lateral aspect of the leg over the distal humerus and one can visualize the vein and two of its branches.
For smaller veins used a tuberculin syringe or a 25 gauge needle on a one cc syringe. Animals may be easier to obtain blood from with a short anesthesia especially if radiographs or other diagnostics need to be done. Small mammals have very delicate skin so sometimes tears may occur with larger domestic animal clippers so be very cautious. Always clean the area before venipuncture as in many cases such as reptiles one will probably encounter bone with the needle and could cause infection.
Sometimes there will be situations where you cannot collect the minimum amount of blood needed for a complete CBC and chemistry panel. For the chemistry panel, if you have an in house analyzer you can do a 50% dilution of blood to sterile water. When your values are obtained double all your numbers for the correct count. If you are using a reference laboratory, they will often work with you when you have smaller volumes and often I will list in order the chemistry values I would like in case they cannot run the full panel. It is best to develop a good relationship with whichever laboratory you use and find out the lowest limits for the panels you may want to run. For a CBC, you can do a slide and one hematocrit tube. A slide will allow you to obtain a differential count, a white blood cell estimate, and the tube will allow a pack cell volume and total protein. I generally try to run fibrinogen levels on all exotic animals especially if you are trying to determine inflammatory trends.
When collecting blood, microtainer tubes (Fisher Scientific Co., Orlando, Florida, USA) can be helpful. Lithium heparin tubes are recommended for birds and reptiles and can be used for mammals if there is not enough blood for a red and purple microtainer tube. It is important to use lithium heparin and not sodium heparin tubes as the latter can interfere with electrolyte determinations. EDTA can result in hemolysis in reptile red blood cells.
In general most of the major laboratories can perform exotic blood profiles and have results the following day. For fish and other aquatic animals Avian and Exotic Laboratory is best but has a longer turnaround time. An in house istat or clinical chemistry analyzer is best so that one can obtain test results quickly and a smaller overall blood amount is needed.