CombinedEnzymic-Jaff#{233}Methodfor Determinationof Creatininein Serum

Concentrations of creatinine, as determined in serum by a method involving the combined use of creatinine ami-dohydrolase (EC 3.5.2.10) and alkaline sodium picrate were found to be factitiously low, owing to a reversal of the enzyme reaction. This effect could be eliminated by con-verting creatine, the product of the enzymic reaction, to creatine phosphate. The combined enzymic-Jaff#{233}method was therefore modified to include creatinine amidohy-drolase, creatine kinase, AlP, and Mg2+ in the reaction mixture. The modified method has good precision. We saw no significant interferences by relatively high concentra-tions of acetone, acetylacetone, ADP, creatine, creatine phosphate, glucose, glycocyamine, or pyruvate. Likewise, no interferences were evident with icteric, lipemic, or hemolytic serum samples. There was an excellen