Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

VI. Hepatobiliary Disease
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TABLE 28-2 Summary of Specificity and Sensitivity of Plasma Chemical Variables in Liver and
Muscle Disease Based on Experimental Studies in Pigeons by Lumeij et al . (1988a, 1988b)
Variable Liver disease Muscle disease
Specificity Sensitivity Specificity Sensitivity
Bile acids — —
GGT — —
AST — —
ALT — —
AP — — — —
CK — —
LD — —
GLDH ( ) a — —
a
Elevated GLDH activity is a sign of extensive liver cell necrosis, as GLDH is a mitochondrial and not a cytoplasmatic enzyme. Liver cell degeneration will not
cause elevated GLDH activities. In the budgerigar ( Melopsittacus undulatus ), GLDH activity in liver tissue is relatively low when compared to humans and
most of the domestic animals including cockerel, duck, turkey, and pigeon ( Lumeij and Wolfswinkel, 1987 ). However, in Amazon parrots with extensive liver
necrosis as a result of Pacheco’s disease, elevated GLDH activities were observed in plasma, which indicates that this variable is also useful in at least some of the
psittacine species (Lumeij, unpublished observations).
no GGT activity could be detected in supernatants of liver
tissue homogenates. This might be explained by synthesis
of GGT during (cholestatic) liver diseases, as has been
reported in mammalian species ( Kaplan and Righetti,
1969 ; Kryszewski et al ., 1973 ). Phalen et al . (1997) found
that 5/5 Amazon parrots with bile duct carcinoma showed
increased GGT activities and suggested that GGT may
prove a valuable tool for early detection and staging of bile
duct carcinomas.
In birds, increased AP activities are predominantly associated
with increased osteoblastic activity, such as skeletal
growth, nutritional secondary hyperparathyroidism, rickets,
fracture repair osteomyelitis, as well as impending ovulation
( Lumeij and Westerhof, 1987 ) (see Section VIII.E).
Increased plasma AP associated with liver disease in birds
is rare ( Ahmed et al ., 1974 ). In the experimental studies
from Lumeij et al. (1988a, 1988b) , AP and CK were never
elevated after liver cell damage, whereas activities of these
enzymes in liver tissue were negligible. Increased activities
of liver enzymes in plasma may indicate recent damage to
liver cells but do not give information on liver function. In
end-stage liver disease (cirrhosis), it is possible to have normal
activities of liver enzymes in the plasma, because active
damage to liver cells has ceased (e.g., Fig. 28-11 ).
In psittacine birds, the use of a good anamnesis and
plasma AST is sufficient to make a tentative diagnosis of
liver disease. When birds are known to have been recently
injected intramuscularly, elevated AST (and ALT) activity
should be interpreted with caution. Including a plasma
constituent that specifically gives information on liver
function, for example, total bile acids, has proven to be of
great value. When liver disease is suspected, a biopsy of
this organ is essential to establish a definite diagnosis.
E . Bile Pigments
The excretion of green urates suggests liver disease in birds
(Galvin, 1980 ; Lothrop et al ., 1986 ; Steiner and Davis,
1981 ). This discoloration is caused by biliverdin, which is
the most important bile pigment in birds (biliverdinuria).
Icterus or jaundice, which is caused by a hyperbilirubinemia,
is seen infrequently in birds. When in chickens both
bile ducts are ligated the concentration of plasma bile pigments
rises immediately but stabilizes after 2 weeks at about
85 μ mol/L, which is a much lower concentration than in
mammals with total biliary obstruction. In sera of healthy
ducks, low levels of bilirubin may be detected and significantly
elevated levels have been reported after experimental
duck virus hepatitis infection. However, the observed levels
of about 17 μ mol/L were well below the serum concentration
of 34 to 51 μ mol/L, which has been mentioned as the level
above which jaundice becomes apparent in humans. The
infrequent occurrence of icterus in birds is explained by the
absence of biliverdin reductase, which converts biliverdin
to bilirubin ( Lin et al ., 1974 ; Lind et al ., 1967 ; Tenhunen,
1971 ). It has been suggested that in birds biliverdin may
be converted to bilirubin by bacteria or nonspecific reducing
enzymes (Lewandowski et al ., 1986) . A yellow discoloration
of avian plasma is often caused by the presence of
carotenoids, which is often misinterpreted as being icteric.
F . Bile Acids
Plasma bile acids (BA) and their salts are formed in the liver
from cholesterol and are excreted in the intestine, where
they assist in digestion of lipids. There is a continuous
secretion of bile in both birds with and without a gallbladder.