Alkaline phosphatase and the International Clinical Enzyme Scale

The wide numeric variation of alkaline phosphatase (ALP: EC 3.1.3.1) values reported from clinical laboratories is clearly revealed by the grossly incompatible data found in large interlaboratory surveys. The authors suggest that this unsatisfactory situation is readily correctable by simply expressing all numeric results on a single scale, the International Clinical Enzyme Scale (ICES). ICES for ALP (ALP/ICES) rests upon a well-defined reference system that relates the IFCC Reference Method for ALP to numerous stable primary and secondary ALP reference materials. The authors show by calibrations with ALP/ICES reference materials that raw coefficients of variation of 25-30% due to reagent, temperature, or instrument differences could be reduced to as low as 2%. ICES and the reference system approach automatically unifies the numeric outputs of the working clinical laboratories by relating all measurements and reference materials to one clearly defined international reference method, yet this concept allows many technologic options in the individual laboratory.