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

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Chapter | 13 Hepatic Function
FIGURE 13-11 Phenolsulfonphthalein (PSP) is a dye that is cleared
exclusively by the kidney and used in renal function tests.
Sulfobromophthalein (BSP) is closely related structurally, but the modifications
result in excretion almost entirely by the liver and its use in
assessment of hepatic function.
intravenous injection of ICG. Three plasma samples are
usually taken between 3 and 15 min after administration
and the ICG concentration measured spectrophotometrically.
It also is possible to estimate plasma volume and
hepatic blood flow ( Ketterer et al., 1960 ). Normal ICG
plasma T ½ and K values for the dog using 0.5 mg/kg ICG
(0.64 μ mol/kg) were reported to be 8.4 2.3 min and
0.089 0.027/minute ( Bonasch and Cornelius, 1964 ).
Using an ICG dose of 1.0 mg/kg (1.3 μ mol/kg), Center et
al. (1983c) reported an ICG T ½ for dogs of 9.0 2.0 min,
a clearance rate 3.7 0.7 ml/min/kg, and a 30-min retention
of 14.7 5.0%. In cats that received an ICG dose
of 1.5 mg/kg, Center et al. (1983b) reported a T ½ of
3.8 0.9 min, a clearance rate of 8.6 4.1, and 30-min
retention of 7.3 2.9%. Using an ICG dose of 0.5mg/kg
(0.64 μ mol/kg) in sheep, Sato (1984) reported a T 1/2 of
4.8 0.5 min, and for heifers using a dose of 0.75 mg/kg
(0.97 μ mol/kg), the T ½ was 3.5 0.8 min.
V . OVERVIEW AND CONCLUSIONS
FIGURE 13-12 Calculation of T ½ for sulfobromophthalein (BSP) in the
horse. After bolus injection intravenously, serum samples were obtained at
6 and 10 min, and the T ½ was calculated to be 2.5 min (normal).
plasma is measured after the intravenous injection of bolus
doses of dye ( Warren et al., 1984 ). Because disappearance
of the dye from plasma follows Michaelis-Menten kinetics,
Lineweaver-Burke analysis provides apparent K m and V max
values for the removal of ICG ( Paumgartner et al., 1970 ).
The maximal dye removal capacity can be estimated from
a small number of submaximal clearance values. Although
such multiple tests are not useful for routine practice, they
provide clinical investigators a sensitive index of hepatic
dye clearance that is independent of blood flow.
For clinical application liver function test as a T ½
and fractional clearance (K) is determined after a single
Conventional tests for hepatic disease provide information
about the integrity of the hepatocytes (ALT, AST, SDH)
and the status of the biliary system (AP, GGT). Hepatic
function can be assessed by estimating the excretory
capacity (bilirubin, bile acids NH 3 ) and synthetic functions
(NH 3 /urea, albumin, fibrinogen, and prothrombin) of the
liver.
For the results of clinical laboratory tests to be of optimal
value, it is essential that the specific purpose(s) of the
test(s) being performed be defined. Tests for hepatic disease
are performed for a variety of purposes including to
confirm the existence of liver disease, to assess the nature
(e.g., hepatocellular injury, cholestasis) and severity of
the disease to determine prognosis, to monitor the clinical
course and response to therapy, and to screen individuals at
risk for the existence of occult liver disease.
Many of the standard tests for liver disease are based
on rather simple biochemical procedures that have been
automated for use in multichannel autoanalyzers. One seldom
obtains the result of a single test for liver disease but
rather a panel of results or a “ liver profile. ” In some situations,
the results of multiple tests of liver injury and function
may be received even when there is no specific clinical
indication for them because, with autoanalyzers, it may be
more efficient to perform a large series of tests than to be
selective.
In a given population of animals, some will have liver
disease and some will not. If a test is applied to the whole
population, a certain number of those with the disease will
have a positive test result (true positives), and some with
the disease will have a negative test result (false negatives).
Similarly, among those without the disease, some will have
a positive test result (false positives), and in some, the test