Trueness Assessment for Serum Glucose Measurement Using Commercial Systems through the Preparation of Commutable Reference Materials

BACKGROUND: Commutable reference materials (RMs) are suitable for end-users for evaluating the metrological traceability of values obtained using routine measurement systems. We assessed the performance of 6 routine measurement systems with validated secondary RMs. METHODS: We tested the homogeneity, stability, and commutability of 5 minimally processed human serum pools according to the standard guidelines. The serum pools were assigned values as per the reference procedure of the United States Centers for Disease Control and were used to evaluate the trueness of results from 6 commercial measurement systems based on enzymatic methods: 3 glucose oxidase (GOD) and 3 hexokinase (HK) methods. RESULTS: The prepared RMs were validated to be sufficiently homogenous, stable, and commutable with the patient samples. Method bias varied for different systems: GOD01, -0.17 to 2.88%; GOD02, 1.66 to 4.58%; GOD03, -0.17 to 3.14%; HK01, -3.48 to -0.85%; HK02, -3.83 to -0.11%, and HK03, -1.82 to -0.27%. CONCLUSIONS: We observed that the prepared serum glucose RMs were qualified for trueness assessment. Most of the measurement systems met the minimal quality specifications.

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

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.

Comparison of measurements for ALT and AST among four domestic reference laboratories / 中华检验医学杂志

Objective To investigate the intralaboratury and interlabomtory variations of measurements for ALT and AST among four domestic reference laboratories. Methods The International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) reference procedures and IFCC procedures without pyridoxal 5-phosphate (PLP) were performed in the reference laboratories. Intralaboratory and interlaboratory CVs were compared with those in 2006 and 2007 IFCC External Quality Assessment Scheme for Reference Laboratories (RELA). Meanwhile, deviations of results for ALT, AST and AST/ALT between two methods were calculated. Results Interlaboratory CVs were generally higher than intralaboratory CVs. Interlaboratory CVs among the 41 laboratories were lower than these in RELA. Results of ALT and AST using method with PLP were higher than those using method without PLP. Difference of AST/ALT ratio between the two methods was significant. Conclusions For reference measurement of the 2 enzymes, interlaboratory CVs of < 3.5 are achievable on frozen serum materials. Measurements on lyophilized materials may have higher CVs. Further studies are needed for the investigation of the differences between results obtained in the absence and presence of PLP.

Investigation of precision and trueness of results from the imported commercial systems for measurement of gamma-glutamyitransferase in serum / 中华检验医学杂志

Objective To investigate the precision and trueness of results from six imported commercial systems for measurement of gamma-glutamyltransferase (GGT) in serum in order to provide reference for the clinical laboratories to verify the target accuracy. Methods Five fresh frozen human serum samples that differed in catalytic concentration were analyzed in two candidate domestic reference laboratories and the target values for GGT were assigned using IFCC reference measurement procedure. The same samples were tested by six commercial systems which were calibrated using the matched calibrator. Each system consisted of five instruments in five laboratories, which had been well maintained before measurement. The data was collected. Precision from the same manufacturer and different manufacturers and biases between target values and mean values from each system were calculated. Results The differences of the mean values for five levels of commercial systems varied from 16. 1% to 35.4%. For the five levels, the coefficients of variation (CVs) of the results from all measurement system were from 5.3% to 8. 8% , and CVs from each level were A 2. 17%- 5.07%, B 4. 21%-10. 98%, C 0. 52%-2. 38%, D 1.35%-2. 59%, E 0. 23%-1..54%-), F 1.83%-2. 38%. Biases between the mean values of each commercial systems and the target values were A 0. 43% -8.41% ), B -1.49% - -13.04% ), C 11.20% -17.73% ), D 0. 19% -4. 62% ), E -0. 30% - -2. 63% ), F 4). 46%-7.90%, respectively. The investigation showed that biases of two manufacturers were less than a quarter of the total allowable error (TAE) of The Clinical Laboratory Improvement Amendments of 1988 (CLIA'88) in the whole range of investigated concentrations and the other two manufacturers' biases could meet a quarter of TAE in a relative limited range. The biases of two manufacturers were near or more than half of TAE in most levels. It also revealed that the biases of more than half of manufacturers were more than a quarter of TAE in the low or high level of investigated concentrations. Conclusions The mean values of each manufacturer were significantly different. The variances of commercial systems from different manufacturers were much higher than those from the same manufacturer. Some imported commercial systems for measurement GGT should be better calibrated with the reference method, especially in the whole measurement linearity.