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any age animals with lytic or proliferative bone lesions.
Horses with colic may have increased levels of intestinal
ALP.
Total Bile Acids (TBA)
TBA are considered the preferred assay for evaluation
of hepatic function. Equines lack a gall bladder and
so secrete bile continuously through the biliary tract.
Normally, most bile acid recycles back through the liver,
with 1-2% going through the intestines. Measuring
TBA is a much better guide to hepatobiliary status
than bilirubin assays. High bile acid levels occur with
severe hepatic dysfunction and liver failure and serve as
important diagnostic and prognostic liver function tests
in horses. It should be noted that increased TBA values
can be found due to prolonged fasting (>3 days). The
higher the TBA levels the less favourable the prognosis.
Bilirubin: increased serum bilirubin levels are not
specific for hepatic disease in the horse and they are
documented with decreased hepatic functional mass,
cholestasis, hemolytic disease or anorexia. Increase in
plasma bilirubin associated with anorexia is due to a
decrease in hepatic uptake and conjugation of bilirubin
by the liver.
Urea: Although the majority of equine hepatopathy
cases have normal serum urea concentrations,
decreased serum urea is associated with more severe
hepatopathies and has prognostic relevance.
Basic Liver Reference Ranges - Adult Horse*
Assay Units Mean Range
Fibrinogen g/L 2.1 0.3-3.9
Serum Amyloid A mg/L 1.3 0-20
Liver Biopsy Beta-2 Globulin g/L 5.3 1.7-8.9
AST iu/L 263 102-350
Liver biopsy is considered the gold standard for the ante
mortem diagnosis of liver disease as it provides valuable
information about aetiology, treatment and prognosis.
Liver biopsy is required to classify the nature of the
hepatic pathology and is used to refine the prognosis in
conjunction with the biochemical parameters. Various
liver biopsy histopathology scoring systems have been
developed, with the degree of fibrosis and bile duct
hyperplasia being reported as important prognostic
indicators. SDH iu/L <5.1 >5.1
GLDH iu/L 3 1-10
GGT iu/L 16 1-40
ALP iu/L 204 147-261
Other less frequently employed biochemical
parameters for liver disease
Triglycerides: these are good indicators of hepatic
lipidosis, as increased serum concentrations are
associated with lipid accumulation in the liver,
interfering with the normal function of the hepatocytes.
52
*These are only basic guidelines for adult horses. Reference
ranges are influenced by age (foals, yearling, adults), breed
(thoroughbred, non-thoroughbred), activity (competition, rid-
ing, stud) and reproduction status.
References.
1.
2.
3.
4.
Last, R D; Hill J M, Vorster J H, Bosch S J & Griffiths C. 2010.
Vetdiagnostix Laboratory Manual 2nd edn. Serrati Publishers,
Pretoria. AC/0492-10.
Latimer K S. 2011. Duncan and Prasse’s Veterinary Laboratory
Medicine:Clinical Pathology. 5th edn. Wiley-Blackwell.
Maxie G. 2016. Jubb, Kennedy & Palmers Pathology of
Domestic Animals 6th edn. Elsevier.
Rossdale & Partners. 2006. Beaufort Cottage Laboratories
Guide to Equine Clinical Pathology. 1st edn.
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