Blood biochemistry: bile acid

Overview

• Cholic and chenodeoxycholic acids (primary bile acids) synthesized in liver from cholesterol   →   conjugated with taurine (preferred) or glycine and excreted in bile as their sodium salts (bile salts).
• Discharged at time of eating to small intestine where they assist in fat digestion.
• Only 2-5% of total bile acids are lost in faces each day - remainder resorbed, pass to the liver where extracted and re-excreted (enteropathic circulation).
• Small proportion reach general circulation - it is these that are measured.
• Sensitive indicator of liver function and of integrity of liver, biliary and intestinal circulation.

Uses

Alone

• Liver function.
  Post-prandial bile acid concentration reported to have the highest sensitivity of any single test for the diagnosis of feline liver disease. 
• Portosystemic shunt    .

Result data

Normal (reference) values

• Fasting reference range: 0-10 umol/l.
• Post-prandial reference range: <15 umol/l.
• Specificity of post-prandial TSBA using cut-off >15 umol/l = 89%.
• Using cutoff >20 umol/l for fasting and post-prandial TSBA specificity = 100%.
• Sensitivity of fasting TSBA using cut-off of >5 umol/l = 83%.
• Sensitivity of post-prandial TSBA using cut-off >15 umol/l = 82%.
• Sensitivity of pre- and post-prandial TSBA decrease if cut-off value >20 umol/l (59% and 74%).
• Abnormal TSBA are specific and sensitive indicator of hepatic dysfunction but do not discriminate the underlying type of hepatobiliary disease.

Abnormal values

• Impaired liver function    , eg toxins, infection.
• Biliary obstruction.
• Portosystemic shunt    .
• Slight to moderate increase (usually <50 umol/l) commonly seen in:
  • Hyperthyroidism    .
  • Hyperadrenocorticism    .
  • Excessive steroid therapy    .
  • Diabetes mellitus    .
  • Cardiac disease    .

Decreased (bile acid)

• May be undetectable in serum of normal animals in random blood samples.
  Need multiple subnormal [bile acid] to diagnosis pathologically low [bile acid].
• Severe intestinal obstruction    .
• Malabsorption (<1 umol/l).

Errors and Artifacts

• Post-prandial TSBA <pre-prandial TSBA, or lack of expected rise in post-prandial TSBA, may occur if there has been:
  • Decreased gastric emptying.
  • Altered intestinal transit time.
  • Ileal disease resulting in lack of absorption of bile acids.
  • Incomplete/lack of stimulation of gall bladder emptying.
  • Small intestinal bacterial overgrowth resulting in bacterial deconjugation of bile acids and decreased ileal absorption.
• May see pre-prandial TSBA >post-prandial TSBA:
  • Interdigestive gall bladder contraction has occurred during fasting.

Sources

Publications

Refereed papers

• Center S A, Erb H N & Joseph S A (1995) Measurement of Serum Bile and Concentrations for Diagnosis of Hepatobiliary Disease in Cats. JAVMA 207, 1048-1054.
• Sutherland R J (1989) Biochemical evaluation of the hepatobiliary system in Dogs and Cats. Vet Clin North Am Small Anim Pract 19 (5), 899-927.
• Center S A, Bladwin B H, Erb H & Tennant B C (1986) Bile acid concentrations in the diagnosis of hepatobiliary disease in the cat. JAVMA 189 (8), 891-896.
• Center S A, Bladwin B H, King J M & Tennant B C (1983) Hematologic and biochemical abnormalities associated with induced extrahepatic bile duct obstruction in the cat. Am J Vet Res 44 (10), 1822-1829.

Other sources of information

• Ettinger S J & Feldman E C (eds) (2000) Textbook of Veterinary Internal Medicine. 5th edn. Philadelphia: W B Saunders & Co.
• Kaneko J J, Harvey J W & Brass M L (eds) (1997) Clinical Biochemistry of Domestic Animals. 5th edn. Boston: Academic Press.
• Duncan J R, Prasse K W & Mahaffey E A (1994) Veterinary Laboratory Medicine. Clinical Pathology. 3rd edn. Iowa: Iowa University Press.