Rapid method for the quantitative determination of serum alkaline phosphatase.

S ERUM ALKALINE PHOSPHATASE ACTIVITY is the enzyme analysis most frequently made in clinical laboratories. It has long been a diagnostic tool and therapeutic index in both liver and osseous disease. Its usefulness could be expanded by a method which would measure alkaline phosphatase activity rapidly, accurately, and with a minimum of technical manipulation. Ideally, the substrate for such a method should be a substance which., following enzyme action, provides its own chromogen directly or by the addition of a simple reagent. This report presents the results obtained with a method using an improved buffered phenolphthalein phosphate substrate.* A semiquantitative procedure, in which this substrate is used in tableted form, has been available for some time as a rapid test for serum alkaline phosphatase activity (1). The substrate solution, which is prepared by dissolving a reagent tablet in water, remains colorless until decomposed by the enzyme. The amount of phenolphthalein liberated under controlled conditions is determined photometrically and is a measure of alkaline phosphatase activity.