Comparison of radioimmunoassay and enzyme methods for quantification of serum bile acids

Background. Measurement of bile acids in biological matrices has always been problematical. The development of accurate and sensitive methods of analysis of bile acids has therefore been the subject of much research. The best techniques of analysis of major bile acids in normal human serum are currently high-performance liquid chromatography (HPLC) and gas-liquid chromatography (GC), but they are time-consuming, expensive and unsuitable for routine clinical use especially in the Italian reality, in which the probability that small laboratories have GC or HPLC is very low. Moreover, for analysis of first level as total bile acid determination, technique as GC and HPLC are also excessive, while for a first screening are suitable other analytical procedures. For this reason, in the present paper, we compared two methods suitable for routine quantification of bile acids in human serum: radioimmunoassay (RIA) and enzyme assay. Methods. The tests used for analysis of bile acids were commercially available. With regard to the enzyme method, we used two different tests. Precision and accuracy were evaluated by a control serum. Bile acids were also determined in the serum of 160 subjects. Results. Neither test based on the enzyme method had the accuracy of the radioimmunological test and they overestimated low concentrations of bile acids. Moreover, the tests were not homogeneous. Conclusions. Our results indicate that the radioimmunological test is valid and reproducible for routine laboratory determination of bile acids in serum. On the contrary, enzyme tests were not satisfactory, at least when performed manually.