Chromatographic and InhibItIon Method for Serum

CLINICAL CHEMISTRY, Vol. 29, No. 2, 1983 407 cause a “rise” (an increase in absorbance over a threshold indicative of a sample peak) in the AST blank channel. The concentration of metronidasole in the primer is critical; too little and the blank channel shows no rise; too much and the AST activity in the test channel isapparently so depressed by the drug that the trigger level (threshold) is not reached. The minimum AST activity to cause a rise is 40 U/L, while the minimum concentration ofmetronidazole to cause a rise in the blank channel is15 mg/L, equivalent to AST activity of about -40 U/L. Consequently, we recommend that the primer be prepared as follows: