Alanine aminotransferase cut-off values for blood donor screening using the new International Federation of Clinical Chemistry reference method at 37 degrees C.

BACKGROUND AND OBJECTIVES: Serum alanine aminotransferase (ALT) determination is recommended, or even required by law, in the screening of blood donors in many countries, and donors with an increased catalytic activity of ALT are excluded from blood donation. In most countries, the ALT cut-off value for blood donor screening for men and women is twice the upper limit of the normal range. The introduction, in 2002, of the new International Federation of Clinical Chemistry (IFCC) reference method, performed at 37 degrees C, required new ALT reference values to be established for healthy individuals and a new cut-off point to be determined for blood donor screening. MATERIALS AND METHODS: We compared ALT values of donor blood units using the previous German standard method, which measures ALT values at 25 degrees C, and the new IFCC reference procedure, where ALT levels are measured at 37 degrees C. RESULTS: We found a linear correlation between the ALT values obtained by the method at 25 degrees C and the new IFCC reference method (37 degrees C) (r = 0.983), and a gender- and age-independent ratio of 0.523. Using this ratio we calculated the new ALT cut-off for blood donations and now propose a new upper limit of 132 U/l (2.20 microkat/l) for men and 86 U/l (1.43 microkat/l) for women. Only 220 of 151 678 blood donations collected over a period of 5 years showed an ALT value higher than the cut-off. None were hepatitis C virus (HCV) positive in serological or nucleic acid amplification technology (NAT) assays. Only 0.006% of all blood donations were positive for antibody to HCV and thus excluded. CONCLUSIONS: With the implementation of the new IFCC reference method for ALT determination at 37 degrees C, we propose a new ALT cut-off for blood donor screening, which, for men, is about three times the upper limit of the normal range and for women about 2.5 times. Our results show that a lower cut-off would probably not yield a higher safety of blood products in terms of detecting viral infections, but would result in a loss of approximately 0.75% of suitable blood donors.

Alkaline phosphatase activity: new assay for the Reflotron system. Results of the evaluation in eight clinical laboratories.

A new reagent carrier, Reflotron ALP, has been developed for the Reflotron 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 of the assay was carried out at eight clinical laboratories. The study of the imprecision using the measurements in human samples resulted in coefficients of variation ranging from 1.3% to 4.6% (within-run) and from 3.2% to 4.0% (day-to-day). The analytical specificity of the Reflotron ALP assay agrees well with ALP methods using a N-methyl-D-glucamine buffer solution. The calibration of the Reflotron ALP assay, however, is related to the reference intervals for ALP methods using a diethanolamine buffer solution. Method comparisons were performed with the ALP method on Hitachi instruments using diethanolamine buffer. Reflotron ALP measurements in blood and plasma in 157 randomly selected split samples showed excellent agreement (slope: 0.99; intercept: 0.7 U/l; median bias: 2.3%; median difference from the 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/l; 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/l (median bias: 8.6%; median difference from the comparison method: 35.6%). Reflotron ALP was compared with three different wet chemistry procedures using different buffer compounds: N-methyl-D-glucamine or diethanolamine or 2-amino-2-methyl-1-propanol. In samples containing predominantly ALP isoforms not of liver origin, the measurements with N-methyl-D-glucamine buffer gave the best fit with respect to Reflotron. In an interference study with 18 drugs, no effect on the test results could be detected. Total bilirubin up to 750 micromol/l and hemolysis up to 1.7 g/l free hemoglobin did not influence the test. Reflotron ALP proved to be an easy and rapid method with excellent precision. The accuracy related to an ALP method using diethanolamine buffer was good. The systematic differences for ALP in samples from pregnant women and adolescents have to be taken into account. The assay is well suited for differential diagnosis of hepatic diseases in decentralized testing.

Production and certification of secondary enzyme reference materials (ERMs). Part 1: Preparation of the sera and some of their properties.

We produced three batches of a human-serum-based enzyme reference material (ERM) enriched with human aspartate aminotransferase (EC 2.6.1.1), alanine aminotransferase (EC 2.6.1.2), creatine kinase (EC 2.7.3.2), and lactate dehydrogenase (EC 1.1.1.27). The added enzymes were not exhaustively purified; thus the final ERMs contained some enzymes as contaminants, of which only glutamate dehydrogenase activity might interfere. The stability during storage and after reconstitution was good. The commutability of the four enzymes in the three ERM batches was also good, except when German or Scandinavian methods for aminotransferases were involved. The temperature-conversion factors for the ERMs were equivalent to those for patients' sera. Reactivation after reconstitution was complete within 5 min and was independent of the temperature of the reconstitution fluid. We believe that these secondary ERMs will aid in the transfer of accuracy between well-defined reference methods and daily working methods so that clinical enzymology results will become more comparable from laboratory to laboratory.