Analytical interference of drugs in clinical chemistry: II--The interference of three cephalosporins with the determination of serum creatinine concentration by the Jaffé reaction.

It is well known that some cephalosporins interfere with the Jaffé reaction for creatinine measurement. This interference varies according to the thirteen instruments and eighteen methodologies studied. Our study has shown that: the proportion of picric acid, NaOH and serum have only a slight effect on the interference; the addition of a buffer to the NaOH solution increases the interference due to cephalothin and cephaloridine, but lessens that due to cefoxitin; dialysis decreases the interference; in kinetic methods, the choice of times at which readings are made influences the magnitude of the interference; a higher incubation temperature increases the effect of cefoxitin and decreases the effects of cephalothin and cephaloridine; pre-incubation with NaOH decreases the interference due to cefoxitin, but has no significant effect on the interference due to cephalothin or to cephaloridine.