Practical problems in clinical enzymology

It is possible to carry out precise determinations of the activity of the clinically important serum enzymes with continuous monitoring (kinetic) methods. Care must be taken that the induction period has passed before the first measurement is taken and that the reading is taken from the zero-order, linear part of the curve. Special precautions must be taken with highly active sera that are also turbid. There are no suitable enzyme standards available at present; therefore, standardization of the instrument is of utmost importance. The instrument must be able to produce the theoretical molar absorptivity of the substrate or cofactor. The instrument must be calibrated for wavelength and absorbance accuracy with nationally accepted standards. Some reference methods are beginning to appear; if widely adopted, they should improve the interlaboratory comparability of enzyme assays. Instrument and method standardization plus well-characterized enzyme standards, when available, will reduce the variability of intra- and interlaboratory enzyme assays.