AVIAN BIOCHEMICAL ANALYSIS

50 AVIAN BIOCHEMICAL ANALYSIS



1 What are some important principles to understand about the use of biochemical analysis in birds?



a. Current understanding of avian clinical biochemistry is in the beginning stages compared with knowledge of biochemical analysis in mammals.

b. Biochemical reference intervals can vary within and between species of birds. The variation may be caused by several factors, including differences in nutrition, environment/geography, instrumentation, methodology, number of animals examined, age, and quality of samples.

c. Although published data are available, thorough, peer-reviewed, controlled studies focused on normal reference intervals or on patterns associated with specific diseases are only available for a few species of pet birds.

d. Because of interspecies variations in analytes, published reference intervals (or those provided by the laboratory) from the species in question should be used as a guide and not as an absolute when interpreting biochemical data.

e. Plasma (lithium heparin plasma only) or serum may be used for avian biochemical testing. Plasma is recommended to harvest the maximum volume of sample fluid possible for analysis and to minimize artifacts related to prolonged contact with the cellular components of blood.

f. Plasma or serum should be promptly separated and analyzed to minimize artifacts.


2 How can in vivo or in vitro hemolysis affect biochemical parameters?



a. Direct interference with the measurement of analytes. The magnitude of interference with the measurement depends on the methodology and instrumentation used.

b. Release of erythrocyte contents that contribute to similar plasma/serum constituents (e.g., AST, LD). There is no direct interference with the actual measurement method. This effect is pronounced when erythrocytes contain higher concentrations of the constituent than the concentration present in plasma/serum.

c. Release of erythrocyte contents that contribute cofactors in biochemical reactions.


3 What are causes of hyperglycemia in birds?



a. Glucocorticoids: endogenous (stress), or exogenous

b. Epinephrine: excitement, “flight or fight response”

c. Diabetes mellitus: described in various psittacines

d. Egg yolk coelomitis: transient increases in glucose seen in affected cockatiels

e. ∼72 hours of starvation in pigeons; not documented in other birds

Compared with mammals, birds have higher normal reference intervals for blood glucose concentrations, generally greater than 150 milligrams per deciliter (mg/dl) and reportedly as high as 800 mg/dl.



4 What are causes of hypoglycemia in birds?


Hypoglycemia may be seen with starvation (as short as 12 hours in some species of birds), decreased hepatic functional mass (diffuse severe hepatitis due to Pacheco’s disease virus, polyomavirus, aflatoxicosis), intestinal parasitism, malnutrition, traumatic injury (described in raptors), enteritis, xylazine administration (documented only in chickens), intestinal malabsorption syndromes, bacterial septicemia (documented in poultry), and spiking mortality syndrome in chickens. Hepatic lipidosis may interfere with the ability of a bird to respond to decreasing glucose concentrations during fasting.



5 What biochemical tests are of use when evaluating the urinary system?


Uric acid analysis is used to evaluate the urinary system, and blood urea nitrogen (BUN) may be useful in detecting early renal disease some species of birds (pigeons).


Changes in other reported parameters (e.g., potassium, phosphorus) have been inconsistently associated with renal disease; however, further investigations are necessary. BUN and creatinine are typically very low in birds (below levels of detection by most methods) and are not routinely used as indicators of renal disease or dehydration in birds.



6 How are uric acid concentrations used in diagnosing kidney disease?



a. Hyperuricemia may be indicative of severe dehydration and severe renal disease (proximal tubular damage).

b. Uric acid is not a sensitive indicator of renal disease because it is primarily secreted in the proximal tubules, and the glomerular filtration rate (GFR) must be decreased at least 80% to detect increases in uric acid concentration.

c. In carnivorous birds (raptors, penguins), uric acid concentrations may increase significantly after feeding. Fasting for 24 hours is recommended when evaluation of kidney function is necessary in these species. Shorter fasting times may be necessary in ill individuals.

d. The association of hyperuricemia with renal disease is not always consistent because some birds with renal failure may have normal concentrations of uric acid.

e. Despite the drawbacks, uric acid is regarded as a useful marker of renal disease if reference intervals for the species in question are available.

f. If hyperuricemia is present, dehydration should be ruled out. Endoscopic examination and biopsy of the kidneys may be necessary to determine if renal disease is truly present and to further characterize the pathologic process.


7 Can urinalysis be of help in the diagnosis of renal disease in birds?



a. Urinalysis of a fresh, voided urine sample may be helpful in diagnosing avian renal disease. However, it is not often performed because of difficulty in obtaining a clean sample (no fecal contamination or urate crystals).

b. In general, noncontaminated urine from healthy birds should be negative to trace positive for protein (negative for ketones, glucose, hemoglobin), with a specific gravity between 1.005 and 1.020. The pH reportedly varies from 6.5 to 8.0, with some species of birds excreting more acidic urine. The sediment may contain squamous cells, spherical urate crystals, few bacteria, and less than three erythrocytes or leukocytes per high-power field (40× dry objective).

c. Yellow to green urine or urates (biliverdinuria) suggests liver disease.

d. Red urine suggests hemoglobinuria, which may occur with intravascular hemolysis (e.g., lead intoxication). However, red-brown discoloration of urine may be seen in healthy pet birds fed with feeds containing animal protein.


8 What are causes of renal disease in birds?



a. Infectious causes
(1) Bacteria: hematogeneous spread or ascending infections from cloaca

(2) Fungal: aspergillosis

(3) Viral: most viral infections that target the kidney (e.g., avian polyomavirus) do not cause significant biochemical changes because birds may die before they demonstrate renal impairment. Some parrots may develop immune complex glomerulonephritis secondary to viral infection.

(4) Parasitic: most often seen in wild birds; however, the effect of these infections on renal function is unknown.

b. Toxic causes
(1) Nephrotoxic compounds (aminoglycosides, others)

(2) Dietary vitamin D excess produces metastatic mineralization and may lead to renal failure and gout.

(3) Biliverdinuria: biliverdin may be toxic to the kidney; however, impairment of renal function has not been thoroughly documented.

c. Amyloidosis (ducks, geese, other wild and zoo birds)

d. Neoplasms: unknown if neoplasms involving kidneys will result in impairment of kidney function, but diffusely distributed neoplasms may destroy a significant portion of the kidneys.

e. Other causes
(1) Severe sustained dehydration

(2) High-cholesterol diet (pigeons)

(3) Diet-induced nephritis (chickens)
(a) High in protein

(b) High in calcium

(c) Deficient in vitamin A


9 What are some important principles to consider when discussing the hepatobiliary system in birds?


The goal of the examination of biochemical parameters (e.g., enzymes, bile acids) is to determine if hepatobiliary disease is present. Hepatobiliary disease is defined here as a pathologic process that results in hepatocellular injury and/or necrosis and/or interferes with liver function (e.g., decreased clearance of bile acids from blood). Both processes may occur simultaneously or as a consequence of each other.


A panel of biochemical parameters may help to determine if the structure or function of the liver is altered and what cellular component of the liver is diseased (hepatocytes, biliary system, or both). Unfortunately, alkaline phosphatase (ALP), a serum enzyme associated with bile ductular epithelium and cholestasis in mammals, is not specifically associated with biliary epithelium in birds. Gamma-glutamyltransferase (GGT) activity increases with liver disease, but its specificity for bile ductular epithelium and cholestasis in birds must be investigated further. Serum/plasma enzyme activity (AST, LD, CK; see Question 10) is primarily used to determine if hepatocellular injury is present and to help localize the disease process to a particular cell type (hepatocytes or myocytes). In domestic animals and birds, increased serum/plasma activity of some enzymes only occurs with reversible or with irreversible (necrosis/death) cell injury, whereas increased activity of other enzymes results from increased enzyme production.


To determine if there is interference with liver function, other biochemical tests are necessary. Liver function tests, such as serum/plasma bile acid concentration, are not specific for a particular hepatic cell type (hepatocytes vs. biliary epithelial cell) because they test the function of the liver as a whole.

Related posts:

  1. ERYTHROCYTE DISORDERS
  2. OVERVIEW: HEMOSTATIC COMPONENTS AND DISORDERS
  3. INTERPRETATION OF THE LEUKOGRAM
  4. METABOLIC ACID-BASE ABNORMALITIES

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Aug 26, 2016 | Posted by in INTERNAL MEDICINE | Comments Off on AVIAN BIOCHEMICAL ANALYSIS

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