Creatinine clearance: enzymatic vs Jaffé determinations of creatinine in plasma and urine

We measured creatinine in plasma and urine samples from 17 normal subjects and 10 renally impaired subjects by four different methods: two enzymatic--Ektachem iminohydrolase and Boehringer Mannheim amidohydrolase--and two Jaffé reaction based--Beckman Astra 8 and Technicon AutoAnalyzer I. Creatinine clearances, standardized for body surface area, were also calculated. In both groups of subjects plasma creatinine values were significantly (p less than 0.05) lower, by 3 to 4 mg/L, when measured enzymatically than when measured by the Jaffé reaction. Additionally, creatinine clearances were significantly (p less than 0.05) greater by at least 30 mL/min when calculated from enzymatically measured creatinine values vs Jaffé method values for creatinine. The benefits of lack of interference with enzymatically measured creatinine concentrations and clearances should be assessed in relation to the lack of agreement with long-established (Jaffé) methods for determining creatinine (and inulin) clearances.