An automated method for the determination of total bile acids in serum

Abstract

An automated modification of the earlier described enzymatic methods [10, 12] for the determination of total bile acids in serum is presented. The procedure involves two main steps, the inactivation of unspecific NADH generating enzyme activity in serum, followed by a transformation of the bile acids by a 3α-hydroxysteroid: NAD-oxidoreductase (3α-HSD) to the corresponding 3-keto compounds. Using an LKB reaction rate analyser, the NAD-containing 3 a-HSD preparation (Sterognost-3α) serves as starting reagent, and the NADH formed is measured as the increase in absorbance at 340 nm. The recovery of bile acid standards in 50 g/l albumin averaged 94% and in sera 91%. Accuracy was evaluated by comparison of the results on fourteen sera to gas liquid chromatography analysis; the means agreed within 2.2% (r = 0.99). A commercial control serum agreed within 1.5% to the recommended value. Precision was estimated on three pooled sera and found to be essentially the same for within run and day to day series, the standard deviation being less than 0.5 μmol/l in the normal serum, and slightly above 0.5 μmol/l in the two above-normal sera. Correlation studies were performed on a series including forty-four sera analysed by the method of Schwarz, Bergmann & Paumgartner [12], (x), and by the present method (y). The resulting regression equation was found to be: y = 1.14x+ 0.6, r = 1.00. The average fasting bile acid concentration in thirty-three healthy subjects was 3.2 + 1.3 μmol/l (x±SD), and the 2 h postprandial concentration was 3.7 ± 1.6 μmol/l (x ± SD). No significant differences were observed between sera from males or females. The method is regarded as specific, sensitive, and rapid.

Key Words:

• bile acids
• liver function test
• LKB reaction rate analyzer
• Sterognost-3α