Enzymatic assay of creatinine in serum and urine with creatinine iminohydrolase coupled glutamate dehydrogenase / 临床检验杂志

ABSTRACT

Objective To develop an improved enzymatic method for assaying creatinine in serum and urine. Methods Cratinine iminhydrolase catalyzes the conversion of creatinine to N-methylhydantoin and ammonia,the later combines with 2-oxoglutarate and NADPH in the presence of glutamate dehydrogenase.Before beginning the reaction sequence,endogenous ammonia is removed by an “ammonia scavenger system”that involves the same auxiliary reaction.The NADPH and 2-Oxoglutarate consumed are restored through a reaction catalyzed by isocitrate dehydrogenase.The activity of this strictly magnesium-dependent enzyme is completely blocked by magnesium-complexing reagent that acts promptly whenever the reaction has started with creatinine iminohydrolase as startor.The reaction is monitored kinetically by measuring the NADPH decrease via its absorbance at 340nm.Results The method affords a simple,rapid,and sensitive assay with good precision and extended linearity.Test results compare closely with the HPLC precedure.The proposed method is not subject to interference from several metablites or from the drugs used commonly in clinics.Conclusion The method is easily automated and is suitable for routine work in clinical laboratories.