Laboratory Assessment of the Bleeding Exotic Animal Patient

Key Points

  • Before a blood sample is collected, carefully weigh the risk to the exotic animal patient against the clinical value of the test results. What will you do with this information? How will it affect your clinical plan?
  • EDTA is the most commonly used anticoagulant in small mammals; lithium heparin is commonly used in birds and reptiles.
  • Whenever possible, make a blood film immediately after venipuncture using fresh blood free of anticoagulant.
  • Most adult small mammal hematocrits range from 30-55%; ferrets generally have packed cell volumes (PCV) that exceed 40-45%. Healthy birds generally have PCV values that range between 35% and 55%. PCV in reptiles often ranges from 20% to 45%.
  • The presence of nucleated erythrocytes and thrombocytes in birds and reptiles interferes with the ability of automated cell counters to separate blood cell populations, therefore manual blood cell counts are necessary.
  • The extrinsic coagulation pathway is much more significant in birds and reptiles.
  • Evaluation of coagulation is in its infancy in birds and reptiles, however prothrombin time and activated clotting time have potential as screening tests.



Hemorrhage in the critical care patient can occur from a number of reasons including trauma, hemolysis, heavy parasite loads, toxic exposure, gastrointestinal ulceration, and even some viral diseases (Fig 1). Coagulopathy or bleeding disorders are possible, but rare causes of bleeding in birds and reptiles.

bleeding cockatiel

Figure 1. There are many causes of hemorrhage in the exotic animal patient. Image by Dr. Ariana Finkelstein. Click image to enlarge.

Clinical signs in the hemorrhaging patient can include depression, pallor, tachypnea, dyspnea, tachycardia, and bounding pulses. Hemorrhage into the brain, spinal cord, myocardium, or lungs can result in acute organ compromise without significant anemia or shock (Hackner 2006). Some patients, particularly reptiles, can be asymptomatic.

Laboratory assessment of the bleeding animal subjectively and objectively evaluates components of the hemostasis system: erythrocytes, thrombocytes, and coagulation factors.



To draw or not to draw?

In cats and dogs with severe hemorrhage, it is standard practice to promptly establish venous access and collect blood for a minimum database before initiating therapy (Hackner 2006). Unfortunately exotic animal veterinarians do not always have this luxury. Carefully consider the potential risk to your patient associated with restraint and handling versus the likely clinical value of test results (Mayer 2013). Also keep in mind that test results are most likely to be useful when venipuncture is atraumatic and quick—which is easier said than done in the tiny, hypovolemic, hypothermic exotic animal. It is also recommended that puncture of the same vessel should not be repeated within 30 minutes (Hackner 2006). Although far from ideal, it may be prudent to collect blood from a tiny patient that has already lost a large volume of blood only after supportive care measures have been instituted.

Whenever possible, prepare a blood film immediately after blood collection using fresh blood before it is mixed with an anticoagulant (Campbell 2006).


Anticoagulant of choice

Quickly transfer the sample to tubes containing anticoagulant (Fig 2). Use gentle, careful inversion and rotation to mix the whole blood sample with the anticoagulant. Ethylenediaminetetraacetic acid or EDTA is most commonly used in small mammals, however EDTA causes hemolysis in some birds and reptiles and lithium heparin is commonly used instead (Hanley 2004). Unfortunately heparin is not without its drawbacks. Heparin can adversely affect cell staining, imparting a blue tinge to the blood film, and heparin promotes thrombocyte clumping (Guzman 2008). Unfortunately heparin can also cause erythrocyte lysis in some taxonomic groups like chelonians (Muro 1998, Fudge 2000, Campbell 2006, Campbell 2007, Saggese 2009). Always check with your lab for specific recommendations.


Figure 1. Use 0.25 to 0.5 mL Microtainer blood tubes (BD Vacutainer Systems; Beckton, Dickinson and Co., Franklin Lakes, NJ USA) in small patients. Click image to enlarge.

After mixing blood with anticoagulant, carefully evaluate the sample for evidence of clots, hemolysis, or contamination with lymph as these findings alter the diagnostic value of the sample (Saggese 2009).


Peripheral blood smear evaluation


The two-slide wedge technique is commonly used to make blood smears although some authors recommend the coverslip method in birds due to the fragile nature of avian blood cells. The choice of technique should be based on operator comfort to produce the fewest damaged cells and best quality smears (Fig 3)(Campbell 2007, Heatley 2010).

blood smear

Figure 2. Use either the two-slide wedge technique or coverslip method to create quality blood films. Image by Reytan. Click image to enlarge.


Examine the technical quality of the blood film, then employ a systematic approach. Begin by evaluating the film at low magnification (10x or 20x). Look at all three regions of the blood film: body of the smear near the blood drop, monolayer where red blood cells do not overlap, and the feathered edge where there is more distance between cells (Fig 4).

Stained peripheral blood smear

Figure 3. Examine all three regions of the blood film including the feathered edge (arrow). Image by ‘coinmac’. Click image to enlarge.

  • Scan for clumping, rouleaux, and agglutination (Fig 5).
  • Assess cell morphology (see below).
  • Hemoparasites are occasionally seen in birds or reptiles and severe malaria (Plasmodium infestation) is a common cause of hemolytic anemia in reptiles (Fudge 2000, Saggese 2009).

Repeat the entire process at oil immersion magnification (100x) within the monolayer area of the blood film.


Red blood cells or erythrocytes


Hematocrit is defined as the fraction of whole blood cells consisting of red blood cells) or erythrocytes. Hematocrit (HCT) and packed cell volume (PCV) are often used interchangeably, however technically HCT is measured using an automated analyzer and PCV is spun. Packed cell volumes are slightly higher than HCT because plasma can be trapped with the spun cells.

In bleeding animal, both PCV and total protein are usually decreased, however PCV can be normal or increased with acute hemorrhage since there may not be enough time for fluid a compensatory response to occur (Hackner 2006).


Comparative physiology


Young animals display lower hematocrits and higher proportions of immature cells. For example, chicks typically have a PCV as low as 24% that increases with age. Adult values are reached at sexual maturity.



Exotic companion mammal red blood cells are the ‘typical’ anucleate, biconcave discs (Fig 6). The average diameter of the rabbit (Oryctolagus cuniculus) red cell is 6.8 μm, which is approximately halfway between the size of cat and dog red cells. The average red blood life span is 57 days in the rabbit, compared to 100-120 days in the dog or 70-78 days in the cat (Box 1) (Lester, Melilo 2007).

 Mammalian red blood cells

Figure 5. Mammalian red blood cells lack a nucleus. The cells are disc-shaped and biconcave. Image by Laura Max. Click image to enlarge.

Box 1. Red blood cell lifespan in select exotic animals (Lester, Melilo 2007)
Species Estimated RBC lifespan (days)
Birds 28-45
Rabbits 57-67
Reptiles 600-800


Most small mammal hematocrits range from 30%-55%, however ferrets (Mustela putorious furo) generally have packed cell volumes that exceed 40%-45% (Box 2). Exposure to isoflurane or sevoflurane causes a rapid and significant drop (up to 33%) in hematocrit and hemoglobin levels in the ferret. This temporary change is particularly prominent with prolonged use of inhalant anesthesia (Marini 1997, Lawson 2006). Normal pet rabbits often have hematocrit values that range from 30%-40%. Values that exceed 45% can indicate dehydration (Melilo 2007).

Box 2. Reported packed cell volume ranges (Quesenberry 2010)
Species Packed cell volume (%)
*Higher HCT possible in normal ferret (sometimes up to 60%)
Chinchilla 35-40
Ferret 36-48*
Guinea pig 39-55
Hedgehog 22-64
Rabbit 33-50


Birds and reptiles

Birds and reptiles have nucleated, elliptical erythrocytes that function similarly to mammalian red blood cells (Fig 7). The avian erythrocyte is significantly larger than in mammals, measuring 12 x 6 μm in the chicken (Gallus gallus domesticus). Reptile red cells are even larger than in birds. Chelonians possess the largest red cells with a mean corpuscular volume (MCV) that exceeds 500 femtoliters (fL). Reptile erythrocytes can reach sizes up to 23 x 14 μm (Campbell 2006). Because of this large cell size, the erythrocyte count of birds and reptiles is relatively low when compared to mammals (Box 3).

snake blood cells

Figure 7. Blood smear from a snake illustrating nucleated red blood cells. Click image to enlarge.

Box 3. Erythrocyte count in select species
Species Red blood cell count (cells/μL)
Chinchilla 340,000 to 420,000
Ferret 701,000 to 965,000
Guinea pig 450,000 to 640,000
Rabbits 510,000 to 790,000
Chicken, turkey 300,000
Wood duck 279,000 +/- 0.22 x 10^6
Lizards 1,000,000 to 1,500,000
Snakes 700,000 to 1,600,000
Chelonians 300,000 to 500,000


Healthy adult birds have hematocrits that generally range between 35%-55%. Avian erythrocytes have a life span of 28-45 days. A short red cell half-life paired with a relatively small spleen (that does not serve as a significant erythrocyte reservoir) means that anemia can develop rapidly. Fortunately erythropoiesis increases dramatically within hours in the bird (Pendl 2013).

The PCV in reptile often ranges from 20%-45% (Box 4). Reptile erythrocytes are extremely long-lived, with lifespans ranging from 600 to 800 days (Claver 2009). It can take up to 2 months for a regenerative response to be detected in the reptile patient (Saggese 2009).

Box 4. Reported packed cell volume ranges in select reptile species
Species Taxonomic name Packed cell volume (%)
Bearded dragon Pogona vitticeps 17-28 (24)
Boa constrictor Boa constrictor 24-40
Desert tortoise Gopherus agassizii 23-37
Green iguana Iguana iguana 25-38
Red-eared slider Trachemys scripta 16-47


Red blood cell morphology

Anisocytosis describes the degree of variability in cell size (Fig 8). The typical parrot erythrocyte has a red blood cell distribution width (RDW) of 10% to 11%. An increase in RDW denotes an increase in anisocytosis. This can be a normal finding however anisocytosis also increases in response to anemia.

Anisocytosis in a mammal

Figure 8. Anisocytosis in a mammal. Image by Dr Graham Beards (Own work) [CC-BY-SA-3.0 (], via Wikimedia Commons. Click image to enlarge.

Polychromatophils are large, immature erythrocytes. Their cytoplasm stains blue in Romanowsky stains.

Polychromasia indicate a regenerative response. The relatively short red blood cell lifespan of rabbits, and particularly birds, means that a slight degree of polychromasia is normal in these species (Lester, Melilo 2007).

During brumation, or the hibernation-like state of reptiles, blood cell production is significantly decreased and a low hematocrit can be a normal finding (Pendl 2013). As reptiles recover from brumation, there can be a marked regenerative response with polychromasia and basophilic stippling of erythrocytes (Claver 2009, Saggese 2009). Increased polychromasia can also be seen in shedding reptiles (Saggese 2009).

Visit the University of Virigina’s RBC Basics for additional information on polychromasia.

Poikilocytosis or variable cell shapes, can be an artifactual error, however this finding is also seen with severe systemic disease that affects bone marrow (Fig 9).

Visit Cornell University’s Red Blood Cell Morphology teaching module for information on various cell shapes of mammalian cells.

Poikilocytosis in a mammal

Figure 9. Poikilocytosis in a mammal. Image by The Armed Forces Institute of Pathology (AFIP) [Public domain], via Wikimedia Commons.

The presence of an occasional Howell-Jolly body is normal in the rabbit, and not a sign of cellular regeneration as in the cat (Fig 10) (Melilo 2007).

Howell-Jolly bodies

Figure 9. Howell-Jolly bodies (arrow) are small, basophilic remnants of the nucleus. Image by P. Mourao and Mikael Häggström via Wikimedia Commons. Click image to enlarge.

Reticulocyte count

Reticulocytes are red blood cell precursors that are larger in volume with less hemoglobin (Fig 11) (Box 5). Given the extremely slow cell turnover rate, only a small percentage of reticulocytes are usually found in the blood of healthy reptiles (Saggese 2009).

 Reticulocytes Human Blood

Figure 10. Reticulocytes are best seen with vital stains, which stains the characteristic clumps of residual cytoplasmic RNA. Image by Ed Uthman via Wikimedia Commons. Click image to enlarge.

Box 5. Reported reticulocyte counts of select reptile species
Species Reticulocytes (%)
Chinchilla 0-2.8
Ferret 1-20 (mean 4)
Rabbit 2-4
Hedgehog 8-14
Birds 1-2
1-5 (psittacine birds)
Reptiles <1%

Plasma or serum proteins

Protein levels are useful in evaluating hydration status or hemoconcentration, which can affect packed cell volume (PCV) (Box 6). Although serum and plasma protein levels are often used interchangeably, plasma protein is generally higher than serum protein because of the presence of fibrinogen (French, Miles 2004).

Box 6. Physiologic and pathologic causes of changes in total protein levels
Hyperproteinemia Hypoproteinemia
  • Dehydration
  • Hypovolemia
  • Acute inflammation
  • Chronic inflammation
  • Neoplasia (e.g. lymphosarcoma, hepatic tumors)
  • Egg production in female birds and reptiles
  • Prolonged hyperthermia
  • Malabsorption/maldigestion
  • Protein-losing enteropathy
  • Severe blood loss
  • Chronic hepatic or renal disease
  • Severe, chronic malnutrition

Total protein in birds is usually about half that seen in mammals (Box 7), although protein levels tend to be higher in birds of prey. Plasma total protein of normal reptiles generally ranges between 3-7 g/dL (Campbell 2006).

Box 7. Reported total protein levels in select species
(Fudge 2000, Campbell 2006, Quesenberry 2010)
Species Total protein (g/dL)
Chinchilla 5.3-6.0
Ferret 4.5-7.4
Guinea pig 4.4-6.6
Hedgehog 4.0-7.7
Rabbit 5.4-8.3
Sugar glider 5.1-6.1
Birds 3.0-4.0
Reptiles 3.0-7.0


Traditionally the biuret method, a colometric analyzer test, has been considered the most accurate method for determining plasma or serum protein in birds like the pigeon (Columbia livia) (Lumeij 1985). Fortunately research has shown that refractometry can be used to accurately measure total protein in non-lipemic plasma from at least some psittacine species (Cray 2008).


Platelets or thromboyctes


Primary hemostasis involves interactions between platelets and the endothelium to form a primary hemostatic plug (Fig 12). This plug temporarily seals over the injured blood vessel in a process that is largely mediated by von Willebrand’s factor and membrane glycoproteins.

hemostasis diagram

Figure 11. primary hemostasis, platelets adhere to subendothelial collagen to temporarily seal over the injured blood vessel. Click image to enlarge.

Platelets are derived marrow from pluripotential stem cells of the bone marrow called megakaryocytes (Fig 13). Platelets are anuclear cells with numerous cytoplasmic granules. On a stained peripheral blood smear approximately 8-15 platelets can be identified per high power field in most mammals (hpf). This number correlates with an estimated count of circulating platelets between 200,000 and 800,000 cells/ul (Box 8). If platelets are clumped on the peripheral blood smear, cellular distribution is uneven and this indirect estimate will be inaccurate. A manual platelet count can be performed using the Natt Herrick or Unopette techniques and a hemacytometer. Most platelets are 1 to 3 μm in diameter, but larger forms can be seen (Jenkins 2008).

Platelets by budding off from megakaryocytes

Figure 12. Platelets are derived from megakaryocytes. Image by パタゴニア via Wikimedia Commons. Click image to enlarge.

In dogs and cats, thrombocytopenia is the most common cause of bleeding disorders. Thrombocytopenia can result from immune-mediated peripheral destruction, poor bone marrow production, sequestration within an enlarged spleen (rare), or peripheral use in severe inflammation (DIC) (Drellich 2009). True thrombocytopenia in rabbits is commonly associated with sepsis (Weiss 2010).



The term thrombocyte is preferentially used to describe nucleated platelets in fish, reptiles, amphibians, and birds. Thromboyctes are derived from a stem cell precursor, not a megakaryocyte. Avian thrombocytes are round to oval, nucleated cells that are smaller and more rounded than erythrocytes, while reptile thrombocytes are elliptical to spindle-shaped. The thrombocyte nucleus is central and dark staining, and the cytoplasm is colorless to pale blue with occasional, azurophilic granules and vacuoles.

Automated counters cannot be used to determine thrombocyte counts because their nuclear:cytoplasmic ratio is similar to that of lymphocytes and the machine tends to group thrombocytes with white blood cells. Estimated counts using peripheral blood smears are also difficult because thrombocytes tend to clump, particularly when exposed to lithium heparin. In most case, thrombocyte numbers as only subjectively estimated as reduced, normal, or increased.

Box 8. Platelet or thrombocyte counts in select taxonomic groups
Cells per high power field Cells/μL
Rodents 8-15
Ferrets n/a 200,000-495,000
Birds 1-2 20,000-50,000*
Reptiles 25-350 per 100 WBCs n/a
n/a: not available

Recognized cases of thrombocytopenia are rare in birds and reptiles, but true thrombocytopenia has been associated with bacterial septicemia (Nevill 2009, Claver 2009). Coagulopathy is also a documented feature of highly pathogenic avian influenza (H5N1). Other viruses associated with significant hemorrhagic lesions in birds include avian polyomavirus, paramyxovirus-1, and herpesviruses (Nevill 2009).


Thrombocyte function tests

Thrombocyte dysfunction syndromes have not yet been described in birds (Claver 2009). Buccal mucosal bleeding time should be performed only after ruling out thrombocytopenia and abnormal clotting factor function (see below) (Hackett 2009). Bleeding time in poultry can be tested by pricking the comb with a needle. Average bleeding time is 8 minutes (Weiss 2010).

Thromboelastography (TEG) objectively evaluates the speed and strength of clot formation (Weiss 2010). Recent research has evaluated normal TEG values in Hispaniolan Amazon parrots (Hispanolian ventralis) (Box 9) (Keller 2011).

Clot stability (G)0.2-4.7 Kd/sc

Box 9. Thromboelastography reference values reported in Hispaniolan Amazon parrots (Keller 2011)
Reaction time (R) 0-36.2 min
Clot formation (K) 0-23.3 min
Maximum amplitude (MA) 113.5-51.8 deg
Reptiles 25-350 per 100 WBCs
Time to lysis (LY30) 0-50.9%

Factor function tests

Secondary hemostasis consists of a series of enzymatic reactions that ends in the formation of fibrin from fibrinogen. Fibrin serves to stabilize the primary hemostatic plug. The coagulation cascade is traditionally divided into three pathways: intrinsic, extrinsic, and common pathways (Box 10). All coagulation factors that participate in secondary hemostasis are produced in the liver. Factors II (thrombin), VII, IX, and X are pro-enzymes that undergo vitamin K-dependent modification before they are secreted by hepatocytes (Hackner 2009, Stokol).

Box 10. Components of the coagulation cascade (Weiss 2010, Hackner 2009, Stokol)
Coagulation cascade pathways Involves Comments
Common Factor X
Activated by exposure of blood to tissue thromboplastin
Extrinsic Tissue thromboplastin
(Factor III)
Factor VII
Final common pathway of thrombin generation and fibrin formation
Intrinsic Factor VIII
Factor IX
Factor XI
Factor XII
Surface activated, requires exposure of blood to subendothelium

Birds and reptiles

Intrinsic pathway factors are absent or present in such small numbers as not to be considered important in the bird (Doerr 1981, Ratnoff 1990, Nevill 2009, Sherwood 2013). Although all three pathways have been recognized in reptiles (Sherwood 2013), factor levels are much lower compared to mammals (Ratnoff 1990, Nevill 2009, Sherwood 2013).


Prothrombin time

As the principal test of the extrinsic clotting pathway, prothrombin time or PT is commonly reported in birds (Box 11) (Weiss 2010). Testing PT requires a source of tissue thromboplastin to initiate clotting such as homologous brain thromboplastin (Innovative Research, Novi, Michigan) (Morrisey 2003, Nevill 2009). Prothrombin time significantly increases when heterologous or mammalian-origin tissue thromboplastin is used (Nevill 2009). Success has also been described with the use of Russell’s viper venom (RVV). Prothrombin time results with RVV are considerably shorter compared to use of mammalian brain thromboplastin but longer than those using homologous brain thromboplastin. Reported PT values vary with the species, sample collection, plasma storage, and assay techniques (Box 12) (Weiss 2010).

Box 11. Screening tests for the evaluation of secondary hemostasis
Test Common Extrinsic Intrinsic
Activated clotting time (ACT) X X
Prothrombin time (PT) X X
Partial thromboplastin time (PTT) X X
Whole blood clotting time (WBCT) X
Box 12. Avian prothrombin times ( Weiss 2010, Nevill 2009)
Species PT (range) seconds PT (mean) seconds
Chicken 9-11 10
Chicken (24 weeks) 10-22 15
Chicken (8 weeks) 13-27
Turkey (40 weeks) 10-27 14
Quail 10-15 12
Pigeon 9-21 14
Kite 8-19.5 13
Vulture 11-17 14
Hispaniolan parrot 9-11 10
Cockatoo 10-16 12

Depending on the reagent used, the PT of iguana plasma ranged 453-831 (Kubalek 2002).


Activated clotting time

When testing activated clotting time (ACT), whole blood is added to a special tube containing diatomaceous earth, kaolin, or glass particles, which activate the intrinsic pathway. This test requires accurate mixing (so tiny samples cannot be used) and the specimen cannot be stored. Nevertheless ACT still has some potential for use in birds and reptiles because the common pathway is tested. Quail ACT is normally less than 3 minutes (Weiss 2010).


Activated partial thromboplastin time

Partial thromboplastin time (PTT) also evaluates the common pathway. In iguana s, PTT ranged from 170-242 s (Kubalek 2002).


Whole blood clotting time

Whole blood clotting time (WBCT) is a crude test in which whole blood is placed within a plain (non-siliconized) glass tube or capillary tube, incubated, and inverted until a visible clot forms. Negative charges associated with the glass initiate the intrinsic coagulation pathway.

Bird blood typically clots within 2-10 minutes. Clotting time is accelerated by contamination with tissue thromboplastin as with difficult venipuncture (Doneley 2010). Whole blood collected from raptors with anticoagulant rodenticide exposure may not clot for an hour or more (Nevill 2009).

Blood clotting tests in reptiles are not commercially available, but some techniques are useful in research applications (Nevill 2009).


Disseminated intravascular coagulation

Disseminated intravascular coagulation or DIC is a hypercoagulable state associated with widespread, intravascular activation of coagulation (Box 13).

Box 13. Laboratory changes commonly associated with disseminated intravascular coagulation (Hackner 2009)
  • Thrombocytopenia
  • Prolonged PT
  • Prolonged PTT
  • Abnormal elevation or reduction in plasma fibrinogen
  • Presence of D-dimers or fibrin split products


Fibrinogen is formed and stored in the liver. Fibrinogen is an acute phase reactant and a hemostatic protein that is important for the final stage of blood coagulation when it is transformed into fibrin (Weiss 2010). A variety of conditions, including inflammation, trauma, and neoplasia, can increase fibrinogen levels (Lumeij 2008). Plasma fibrinogen levels in the normal bird range from approximately 100-300 mg/dL (1-3 g/L) (Weiss 2010).

Fibrin split products (FSPs) are fragments created by dissolution of the thrombus or clot that are removed from circulation by the liver. D-dimer are unique FSPs that are formed when cross-linked fibrin is lysed by plasmin (Hackner 2009, Weiss 2010). The presence of D-dimer indicates activation of thrombin and plasmin. Elevated FSPs or D-dimer levels can be seen with DIC, but are not specific for DIC. Furthermore patients with DIC do not always demonstrate elevated levels (Hackner 2009).


Reference values

Most of the scientific information regarding avian hematology is the result of domestic fowl research. All other investigations into bird and reptile hematology, particularly coagulation screening, are essentially in their infancy. Many of the difficulties and challenges associated with non-mammalian hematology are related to the vast number of species that exist. There are more than 9000 bird species, but fortunately the morphology of avian blood cells is relatively homogeneous between orders.

Class Reptilia consists of nearly 8000 species. Reptile hematology is very similar to that of birds, however reptiles are a more heterogeneous group so it can be more difficult to extrapolate information between species. (Claver 2009).

Reported reference ranges should serve as general guidelines only. Use patient history and clinical status to interpret hematologic values as a wide variety of factors can significantly influence reference values (Box 14).

Box 14. Factors that can influence hematologic reference values
(Fudge 2000, Campbell 2007, Saggese 2009, Heatley 2010)
Intrinsic factors Extrinsic factors
  • Species
  • Gender
  • Age
  • Physiological status
  • Breeding season
  • Hibernation
  • Season
  • Temperature
  • Habitat or husbandry
  • Diet
  • Living conditions (e.g. free-living versus captivity)
  • Venipuncture site


Laboratory assessment of the bleeding animal subjectively and objectively evaluates erythrocytes, thrombocytes, and clotting factors. Small mammals possess the ‘typical’ anucleate, biconcave disc-shaped erythrocytes, while birds and reptiles possess large, nucleated erythrocytes that are elliptoid to fusiform in shape. With the exception of the ferret, most bird and small mammal hematocrits range from approximately 35-55%. Ferret hematocrits normally exceed 40%-45%. The packed cell volume tends to be lower in reptiles often ranging from 20% to 45%. Thrombocytes are nucleated platelets in birds and reptiles. Manual blood cell counts are required in birds and reptiles because the presence of nucleated erythrocytes and thrombocytes interferes with the ability of automated cell counters to separate blood cell populations. Although factors from all three coagulation pathways have been found in some bird and reptile species, intrinsic pathway factors are absent or present in much smaller numbers when compared to mammals. Use of coagulation factor screening tests is in its infancy in exotic animals, but use of prothrombin time, activated clotting time, partial thromboplastin time, and even whole blood clotting time has been described.



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Pollock C. Laboratory assessment of the bleeding exotic animal. May 31, 2013. LafeberVet website. Available at