Enzyme reference materials: their place in diagnostic enzymology.

The method-dependency of measurements of enzyme activity presents problems of interpretation and comparison. Enzyme calibration materials may provide results in agreed-upon units of catalytic concentration while allowing a choice of routine methods. However, this requires the calibrating and calibrated methods to be equally specific, close agreement in intermethod ratio to exist between the calibrator and target enzyme in serum, and absence of significant sample-dependent variation in the intermethod ratio.