- The average blood volume of most birds is approximately 10% of body weight. Ten percent of this volume or 1% of the bird’s body weight may be removed for testing.
- Avian red cells are nucleated which is why manual white cell counts are typically not possible.
- White cells are similar to mammalian lines, except that mammalian neutrophils are replaced with heterophils and mammalian platelets are replaced with thromobocytes.
- Important differentials for leukocytosis with profound heterophilia and monocytosis include chlamydophilosis, aspergillosis, and tuberculosis.
- Heparinized samples are suitable for biochemistry.
- Muscle damage, which may include intramuscular injections, can cause elevations in the enzymes creatine kinase, aspartate aminotransferase (AST), and lactate dehydrogenase (LDH).
- Liver damage is associated with elevations in the enzymes glutamate dehydrogenase, LDH, and AST.
- Hypercalcemia, hypeglobulinemia, and an elevation in alkaline phosphatase may be seen in the laying hen.
In order to reach a correct diagnosis, the clinician must put aside sufficient ‘quality time’ to work up the case. While blood work is indeed important, even that remains just ‘part of the picture’ (Fig 1). All too often, when a clinician is unfamiliar with a species, the reaction is often to rely on laboratory results to hang a diagnosis upon. Although we have all been guilty of this, such an approach is inappropriate. For each sick bird, the following diagnostic tools should be applied: complete history, visual examination of the bird and its environment, physical examination, clinical pathology sample collection (blood, feces, swabs, aspirates, etc.), and radiography (at least two views at right angles). Only at this stage may one decide if more specialist techniques are required such as endoscopy, ultrasound, or electrocardiogram.
Use a 23 or 25 gauge needle. If the sample is slow to draw due to vein collapse as suction is applied, clotting of the sample can result. For novices sampling smaller species, the syringe and needle may be flushed with dilute (1:100) heparin to prevent clotting.
The average blood volume of most birds is approximately 10% of body weight. Ten percent of this volume may be removed from circulation for testing (or 1% of the bird’s body weight). For example, up to 3 ml may be collected from a 300 g parrot. However be sure to consider the volume lost from circulation in a hematoma, as well as that collected in the syringe.
Some species are easily restrained for blood collection, in others stress to the patient may be reduced by use of isoflurane or sevoflurane anesthesia. Heparinized samples are suitable for biochemistry, including glucose. Blood may be collected from the basilic, medial metatarsal, or right jugular veins.
Consider factors that will alter the value of test results. If tests are conducted in-house, there must be appropriate quality control, the test parameters must be of value, and the clinician must know how to correctly interpret test results. Consider the time of day the sample is taken, postprandial effects, sample handling or transportation artifacts, and potential delays in testing. Whether the sample is tested in-house or at a quality controlled commercial laboratory, the availability of normal values is mandatory. Use external laboratories accustomed to the species with which you are dealing. Check that the lab has normal parameters and seek advice on sample collection, handling, and transportation recommendations.
An inappropriate test, or poor quality sample is bad. A wrongly interpreted sample is worse than not testing the bird in the first place.
Normal values should be specific to the laboratory in question, but even so a wide variation in normal values can be anticipated depending on age, sex, reproductive status, housing, activity level, etc. There is great benefit to be gained by sampling patients on an annual basis, firstly in the search for subclinical disease but also so that individual’s normal blood values can be recorded on file.
Complete blood count
Most if not all hematology can be readily conducted in-house, and is the most beneficial and useful part of clinical pathology. Speed is of an essence and being able to differentiate as to whether the condition is infectious or non-infectious, if anemia is present, and if so is the bone marrow responding is invaluable.
The complete blood count (CBC) will reveal the:
- Number and character of red blood cells
- Number, percentages, and characteristics of white blood cells
- Concentrations of solids in the plasma
- Number of thrombocytes in circulation
- Presence of blood parasites or other morphological changes, which could lead to anemia
Avian red cells are nucleated which is why automated white cell counts are typically not possible. Regenerative anemia is represented by increased polychromasia.
White blood cells are similar to mammalian lines, except that mammalian neutrophils are replaced with heterophils and mammalian platelets are replaced with thromobocytes. There are significant variations in normal differentials among avian species, in particular the total white cell count and the heterophil:lymphocyte ratios.
Interpretations that can be made are listed below in Table 1.
|Table 1. CBC findings|
|Leukocytosis||Infection, inflammation, necrosis, neoplasia, heavy metal toxicosis, and stress (particularly in macaws, there should be no toxic changes in white cells)|
|Severe heterophilia||Chlamydophilosis, aspergillosis, tuberculosis (often with toxic changes in white cells)|
|Moderate heterophilia||Infection, cellular necrosis|
|Lymphocytosis||Viral infection, certain stages of Chlamydophilosis|
|Monocytosis||Chronic infection with extensive necrosis and phagocyte activity (typically aspergillosis, chlamydophilosis and tuberculosis)|
|Eosinophilia||Of inconsistent and unproven significance|
|Basophiia||Uncommon result most often associated with respiratory infections, resolving tissue damage, parasitism and some stages of Chlamydophilosis|
|Leukopenia||Overwhelming bacterial or severe viral infection (particularly circovirus). Leukopenia may also be associated with reduced production of cells or increased use, which is demonstrated by the presence of immature or toxic white cells|
|Table 1. Biochemistry parameters in avian patients|
|Alanine transaminase (ALT, SGPT)||No value in birds|
|Albumin||Reduced albumin production or loss of albumin via gut or kidney||As in mammals, albumin is responsible for maintaining osmotic pressure and as a transport protein.|
|Alkaline phosphatase (ALP)||Physiologic (i.e. increased medullary bone density in the hen) or pathologic bony changes (i.e. fractures, infection, neoplasia)||Not useful in the diagnosis of avian liver disease.|
|Amylase||A mild elevation is typically associated with gastrointestinal disease, marked elevations (>4x maximum range) are typically associated with pancreatic disease.||Difficult to interpret|
|Aspartate aminotransferase (AST, SGOT) *||The last enzyme to rise after muscle or liver damage (72 hrs post- damage) and also the last to normalize.||Primary sources are muscle, liver, and kidney. Although not specific for liver, elevations may suggest liver disease.|
|Bile acid||Elevations indicate liver dysfunction. If a high level is detected, the sample should be repeated. After two high results liver biopsy is indicated, in order to determine the cause of liver dysfunction.||Pre-sampling fasting is required in birds with no gall bladder (e.g. pigeons and parrots).|
|Calcium||Hypercalcemia in psittacine may occur secondary to vitamin D toxicity but elevated calcium levels will also be seen just before egg laying. Polyostotic hyperostosis (increased medullary bonedensity) may be seenin the shafts of the long bones in laying hens. Hemolysis can cause false elevation, as can lipemia.||Hypocalcemia is an important cause of seizures in African grey parrots.||As in mammals, total calcium is linked to plasma protein levels. Ionized calcium is more useful, as elevations or declines in totalcalcium may or may not affect functionally available (ionized) calcium.|
|Cholesterol||May be associated with starvation, liver disease,hypothyroidism or excessive fatty diet||Inconsistent significance|
|Creatine kinase(CK) *||Muscle damage, intramuscular injections, or catabolic states (weight loss due to inanition or disease).||The half-life is approximately 16 hrs.|
|Globulin||The most common reason is antibody production in egg production, however globuilin levels may also rise with immunological reaction against infection, inflammation or neoplasia.|
|Glucose||Stress, starvation after eating, persistent elevation in diabetes||Sepsis, starvation. |
A very low sample can also occur if a whole blood sample sits for 24 hours or more due to the presence of nucleated red blood cells.
|Glutamate dehydrogenase (GLDH)||Liver cell damage (elevations can also be consistent withdamage to kidney and brain)||The most consistently useful tissue enzyme for liver cell damage|
|Lactate dehydrogenase (LDH) *||Present in cardiac and skeletal muscle and liver|
|Phosphorus||Chronic renal failure||Inconsistent|
|Potassium||Renal disease, acidosis, adrenal disease, hemolysis,||Diarrhea and alkalosis|
|Protein (total)||Dehydration, immune stimulation||Malnutrition, malabsorption, renal disease, liver disease||Should be measured by the biuret method for accuracy, although a temperature compensated refractometer is acceptable if the sample is not lipemic. Best to assess with A/G ratio.|
Elevated 4-5X indicates dehydration
|Limited value, not an indication of renal function.|
|Uric acid||Impaired renal function, dehydration, or physiological elevation within 12 hours of feeding in raptors.||The kidney removes 90% of the blood uric acid, and 50% of the kidney must be destroyed to affect blood uric acid levels. Normal levels are not indicative of no renal damage.|
|*If the enzymes creatine kinase (CK), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) are all elevated this likely indicates muscle damage. Intramuscular injections can cause elevations. If AST and/or LDH are elevated in the absence of CK elevation, this is typically indicative of liver damage, however relative half-lives of different enzymes should be considered. CK has a short half-life compared with AST, so after muscle injury CK can have returned to normal while AST is still raised. This could be interpreted as being liver derived while in fact it was muscle related. AST is the last enzyme to rise after muscle or liver damage (72 hours post-damage), but also the last to normalize.|
Download the PDF Table: Biochemistry Parameters in Avian Patients
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Fudge, AM. Laboratory Medicine: Avian and Exotic Pets. Philadelphia: WB Saunders; 2000.
Lumeij JT. Avian Clinical Biochemistry, In: Kaneko JJ, Harvey JW, Bruss ML (eds). Clinical Biochemistry of Domestic Animals, Academic Press; 1995: 857-883.
Forbes N. Avian hematology and biochemistry panels. January 29, 2008. LafeberVet Web site. Available at https://lafeber.com/vet/avian-hematology/