Simple, rapid determination of serum guanase activity with the Hitachi 736 automated discrete analyzer

In this new method for determining serum guanase activity by use of the Hitachi 736-40 automated analyzer, serum is incubated with a mixture of xanthine oxidase, superoxide dismutase, and catalase; a reagent containing KCN, guanine, nitrotetrazolium blue, and Triton X-100 is added; and the increase in absorbance at 570 and 660 nm is measured for 2.4 min. Only 20 microL of sample is required, and results are linearly related to the activity concentration of guanase up to 30 U/L. Within-run and day-to-day precision (CV) was respectively 2.6 to 4.2% and 3.5 to 5.5% over 0-30 U of guanase activity per liter. The normal reference interval, as calculated from data on 40 healthy persons, is 0.1 to 2.2 U/L. Results correlate well (r = 0.997) with those by a kinetic method (Clin Chem 27: 560, 1981). The guanase activity of 150 samples can be measured within 1 h by this method.