Evaluation of immunonephelometry of C-reactive protein in serum.

A recent Letter to the Editor (Clin. Chem. 25:812, 1979) deals with inhibition by bilirubin of y-glutamyltransferase (EC 2.3.2.2) in the Du Pont aca. We also studied this (I), and agree with the author. To overcome this problem, we propose that serum with high concentrations of bilirubin be diluted with physiological saline, 100-fold being the most convenient dilution in view of the fact that A/min of this dilution at 405 nm most nearly approximates that of a serum within the range between normal and pathological. Accuracy is not greatly affected by this dilution step. With a 10-fold dilution, zA/min is too high, because the concentration of bilirubin may still be high enough to continue to produce inhibition. With a dilution of 1000-fold dilution the enzyme activity declines disproportionately and results are inaccurate.