The evaluation of trueness of 4 α-amylase measurement systems

Objective To investigate the routine methods of α-amylase (AMY) test in serum which meets the requirements of ISO 15189. Methods Fifty human serum samples with different concentrations of AMY (40-750 U/L) were collected from March to December in 2008, to form the patients′ frozen serum group.Four AMY measurement systems including Roche，Wako，MINDRAY and MAKER were used.The frozen standard materials with concentrations of (70.1±3.7) U/L and(418.3±22.1) U/L and the patients′ frozen serum group were measured simultaneously by using IFCC reference method and 4 AMY measurement systems based on 7170A automatic biochemistry analyzer.The linear regression analysis was made between the measurement results of each system and IFCC reference method.The equivalence, agreement and trueness were also evaluated by using the file EP9-A2 method ,Bland-Altman Graphical-Analysis and the improved Bland-Altman Graphical-Analysis of MVS1.80 software. Results Judging by the standards of IFCC reference method, the measurement results of 4 measurement systems were obviously different. (1) When measuring standard materials the results were 66.4，70.6，69.4 and 49.2 U/L respectively and 394.0，456.4，406.7，302.4 U/L respectively.The measurement results of MINDRAY were in agreement with that of IFCC reference method.(2) When measuring the patients′ serum group by 4 measurement systems and IFCC reference method, the slopes of the linear regression equations were 0.934,1.070,0.930 and 0.731,respectively.And the intercepts were 0.886, 6.249, 5.388 and 3.574, respectively.According to the EP9-A2 method, the measurement results of Roche Wako, MINDRAY were equivalent to that of IFCC reference method.According to Bland-Altman Graphical-Analysis, the measurement results of Roche and MINDRAY were in agreement with that of IFCC reference method.The average biases of each measurement system were -6.11% (“Average bias±2s” were 2.81% and -9.40%), 1.99% (“Average bias±2s” were 10.35% and -6.36%), -2.70% (“Average bias±2s” were 2.37% and -7.77%) and -34.72%(“Average bias±2s” were -24.20% and -45.24%)，respectively.According to the improved Bland-Altman Graphical-Analysis, the measurement results of MINDRAY are correct.The average biases of each measurement system were -5.92% (“Average bias±2s” were -2.81% and -9.03%), 2.10% (“Average bias±2s” were 10.74% and -6.53%), -2.64% (“Average bias±2s” were2.24% and -7.51%) and -29.51% (“Average bias±2s” were -21.82% and -37.21%)，respectively. Conclusions (1) The measurement results of different measurement systems do not necessarily have crrect results though they have claimed to have traceability.(2) The trueness of measurement results using the same system may not come to the same conclusion when evaluated by different methods.So laboratories should select and establish a procedure to evaluate trueness of routine methods and adopt those meeting the trueness requirements of ISO 15189.（Chin J Lab Med, 2012, 35:309-316） Key words: alpha-Amylase; Reference standards; Laboratory techniques and procedures; Evaluation studies