The effect of haemolysis on the measurement of plasma alkaline phosphatase activity.

The non-dialysable fraction of haemolysate causes an apparent reduction of plasma alkaline phosphatase (ALP) activity using 4-nitrophenylphosphate as substrate. Analyses using four different buffers showed that the decrease in enzyme activity is affected by the buffer used. The percentage reduction in ALP activity is dependent on the initial ALP activity but not on the isoenzyme present. When diethanolamine was used as buffer, sample blanking almost completely compensated for the apparent reduction in enzyme activity. However, when aminomethylpropanol, aminomethylpropanediol and tris-carbonate buffers were used, it appeared that haemolysate reduced the catalytic activity of the enzyme, since sample blank correction had minimal effect on the results.