Serum alkaline phosphatase measured by using thymol blue monophosphate and a bichromatic analyzer.

Thymol blue monophosphate is evaluated as a substrate for use in kinetic bichromatic analysis of serum alkaline phosphatase activity. The effect of abnormally high concentrations of hemoglobin, bilirubin, or chylomicrons is negligible. The expected range for ambulatory adults established by assaying sera from 206 blood donors, was 12-44 U/lliter at 37 degrees C. Comparison of the method with a commonly used p-nitrophenyl phosphate method yielded a correlation coefficient, r, of 0.9949. Advantages of the method are the reduced cost per test and the exceptionally stable substrate.