Enzyme activities in urine: how should we express their excretion? A critical literature review.

Different methods and reference bases for characterizing the excretion of urinary enzymes (relation to volume, time, creatinine, specific gravity, osmolality and fractional excretion) are reviewed with regard to their advantages and disadvantages when using urinary enzyme excretion as a diagnostic tool. The problems of timed and untimed urine samples for the analysis of urinary enzyme excretion and the influence of diuresis on the quantity and composition of enzymes excreted are discussed. The use of the second morning urine as a random urine sample, and determination of the relation of enzyme activity to urinary creatinine (enzyme/creatinine ratio; enzyme/creatinine index) represent a satisfactory compromise for the characterization of urinary enzyme excretion. The calculation of enzyme excretion per unit time or other modes of expression should be used only in special cases.