Accuracy investigation of commonly used creatinine assay systems / 中华检验医学杂志

ABSTRACT

Objective To evaluate the accuracy of Cr measurement value from commonly used homogenous detection systems,to investigate the variation among different systems and the corresponding bias of eGFR.Methods According to the CLSI EP14-A2 protocol,commutability of LN24 was validated among 10 enzymatic assays and 1 picrate assay.LN24 included 6 vials of solution with Cr values assigned by IDMS at NIST,and concentrations of Cr for each vial were 68.1,126.9,185.7,244.5,303.2 and 361.9μmol/L LN24 was used to evaluate the accuracy of the included systems and the variation among them,and the assigned values were taken as the target values.eGFR were calculated by MDRD equation using IDMStraced picrate Cr and CKD-EPI equation using enzymatic Cr.Results Commutability was exist among the 11 systems for LN24 detection.Four systems showed bias ＜ 4.4 μmol/L at each level of LN24,two system showed bias ＞4.4 μmol/L at each level of LN24,one system showed a fixed negative bias( -4.2 ±0.7)μ mol/L,the other 4 systems showed diverse bias at different levels.Cr-bias-caused eGFR bias could reach 14.9 ml · min-1 · (1.73 m2) -1 at Cr level of 68.1 μmol/L SD among systems ascended with Cr level (2.6 -6.1 μmol/L) ;CV among systems descended with Cr level(4.0％ - 1.7％ ) ;After the 2 systems with obvious negative bias were removed,SD,CV among systems and eGFR bias decreased obviously.By measuring fresh serum,it was found that Cr bias among enzymatic systems was mostly ＜ 10 μmol/L;that between enzymatic assays and picrate assay was much diffused(from - 15 to 20 μmol/L).When Cr ＜ 100μmol/L,the eGFR difference between result of MDRD equation and that of CKD-EPI equation ranged from - 18 to 40 ml · min-1 (1.73 m2) -1.Conclusions Some enzymatic systems show good accuracy.Difference of Cr value is relatively fixed among enzymatic systems,and comparability can be reached through mathematic way.Un-acceptable difference between picrate assay and enzymatic assays still exists,thus comparability cannot be reached through mathematic way.At low Cr level,bias of Cr and using different equations may lead to significant bias of eGFR.We recommend that clinical laboratory should pay much attention to the accuracy and comparability at low level of Cr,and use uniform equation to calculate eGFR.