Alkaline phosphatase activity: New assay for the Reflotron (R) system. Results of the evaluation in eight clinical laboratories

A new reagent carrier, Reflotron (R) ALP, has been developed for the Reflot ron (R) system, allowing easy and rapid measurement (in less than 3 minutes ) of alkaline phosphatase (ALP) activity in capillary blood, venous blood, heparinized plasma or serum. The evaluation of the analytical performance o f the assay was carried out at eight clinical laboratories. The study of th e imprecision using the measurements in human samples resulted in coefficie nts of variation ranging from 1.3% to 4.6% (within-run) and from 3.2% to 4. 0% (day-today). The analytical specificity of the Reflotron (R) ALP assay a grees well with ALP methods using a N-methyl-D-glucamine buffer solution. T he calibration of the Reflotron (R) ALP assay, however, is related to the r eference intervals for ALP methods using a diethanolamine buffer solution. Method comparisons were performed with the ALP method on Hitachi instrument s using diethanolamine buffer. Reflotron (R) ALP measurements in blood and plasma in 157 randomly selected split samples showed excellent agreement (s lope: 0.99; intercept: 0.7 U/I; median bias: 2.3%; median difference from t he comparison method: -0.3%). Specimens from pregnant women and adolescents were excluded from this study. Differing values were obtained in a method comparison using 48 samples containing predominantly the ALP bone isoform ( slope: 0.81; intercept: 31.5 U/I; median bias: 5.7%; median difference from the comparison method: -12.2%). Regression analysis of the results from 21 sera with prevailing placental ALP gave a slope of 1.51, and an intercept of -41.1 U/I (median bias: 8.6%; median difference from the comparison meth od: 35.6%). Reflotron (R) ALP was compared with three different wet chemist ry procedures using different buffer compounds: N-methyl-D-glucamine or die thanolamine or 2-amino-2-methyl-1-propanol. In samples containing predomina ntly ALP isoforms not of liver origin, the measurements with N-methyl-D-glu camine buffer gave the best fit with respect to Reflotron (R) In an interference study with 18 drugs, no effect on the test results could be detected. Total bilirubin up to 750 mu mol/l and hemolysis up to 1.7 g/ l free hemoglobin did not influence the test. Reflotron (R) ALP proved to be an easy and rapid method with excellent prec ision. The accuracy related to an ALP method using diethanolamine buffer wa s good. The systematic differences for ALP in samples from pregnant women a nd adolescents have to be taken into account. The assay is well suited for differential diagnosis of hepatic diseases in decentralized testing.