Evaluation of the spectrophotometric assay of guanase with 2,2'-azino-di(3-ethylbenzthiazoline-6-sulphonate) (ABTS) as chromogen.

A simple spectrophotometric assay for serum guanase based on the oxidation of 2,2'-azino-di(3-ethylbenzthiazoline-6-sulphate) (ABTS) using xanthine oxidase, uricase and peroxidase is described and statistically examined through its application to normal and pathological sera. The method is very sensitive, precise (CV below 8.13%) and linear up to 152.5 U/l. Comparison with the methods of Hue & Free ((1965) Clin. Chem. 11, 708-715), and Giusti ((1974) In: Methods of Enzymatic Analysis, Bergmeyer, H. U., ed., p. 1086), and Ito et al. ((1981) Clin. Chim. Acta 115, 135-144) gave a good correlation (r greater than or equal to 0.969). The reference values for the ABTS-method are 2.93 to 23.92 U/l (mean = 13.57 U/l, CV = 22.43%). The mean values of guanase activities determined in sera of patients with different liver diseases (mean = 30.29 U/l), or chronic alcoholics (mean = 35.41 U/l) were significantly higher than normal. The patients with chronic diseases had significantly lower activity (mean = 7.22 U/l, t = 9.25, p less than 0.001).