Metrological traceability of values for alpha-amylase catalytic concentration assigned to a commutable calibrator materials.

BACKGROUND: The International Standard ISO 18153 describes how to assure the metrological traceability of catalytic concentration values assigned to commercial calibration materials following the reference measurement system. We applied this approach to the standardization of alpha-amylase measurements. METHODS: Traceable values of catalytic activity with measurement uncertainty were assigned to three commercial calibrator materials using alpha-amylase primary reference measurement procedure described by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC). The metrological traceable to the SI units calibration was validated by measuring human serum and plasma samples using the primary reference procedure and two routine commercial measurement procedures using different substrates (4,6-ethylidene(G1)-4-nitrophenyl(G7)-alpha-(1-->4)-D-maltoheptaoside (EPS) and 2-chloro-4-nitrophenyl-alpha-D-maltotrioside (CNP)) and calibrated with the traceable materials. Previously the commutability of the commercial calibration materials was verified. RESULTS: Procedures comparison showed that the primary reference procedure and routine procedures have the same analytical specificity. The commercial calibrators tested showed to be commutable and were used to recalibrate the routine measurement procedures. The agreement of procedures improves after recalibration with commutable calibrator materials. CONCLUSIONS: The implementation of a reference system for alpha-amylase measurements was demonstrated that assures the traceability of patients' results to SI units and to harmonize the results obtained by two different routine procedures.

SCE Nordic alpha-amylase study. II: Assessment of proposed calibration procedure. A report by the Scandinavian Committee on Enzymes (SCE).

Eighty-seven Nordic Hospital laboratories participated in a joint SCE-NORDKEM follow-up study of the long-term stability of the previously established calibration factors for a number of alpha-amylase routine methods based on six different substrates. Human control materials with 90% pancreatic, 90% salivary, and pure pancreatic alpha-amylases were measured by the participants. The data were plotted before and after calibration of each method using a human pancreatic calibrator with an assigned catalytic concentration of 390 U/l (Phadebas blue starch method, 37 degrees C). As in the previous study, carried out 9 months earlier, the pre-calibration values varied over a six-fold range. The post-calibration values of all methods except those based on a tetraose substrate showed an acceptable inter-laboratory comparability. As a temporary measure, SCE recommends that the Nordic laboratories calibrate the accepted routine methods by their individual calibration factor. Detailed suggestions for calibration procedures and a discussion of the principles of transferability will shortly be published by the SCE in this journal.