Development of a clinically useful colorimetric method for serum lipase

Sodium cholate has proved to be a more reliable activator of human pancreatic lipase in human serum than the unsatisfactory sodium taurocholate, which has been useful in the measurement of dog serum lipase. Since both activators work well on human pancreas alone, human serum plays a role in determining the ability to detect human pancreatic lipase with either activator. A method for the determination of human serum lipase which takes advantage of this species difference has been developed. This new method utilizes well buffered sodium cholate as a reliable activator and β-naphthyl myristate as a substrate. The advantage of the myristate over the laurate ester of β-naphtyl is the slower rate of hydrolysis of the former by serum esterase. As little as 0.2 μg. of a pooled extract of human pancreas added to 0.2 ml. of human serum can be detected. Lipase activity can be demonstrated in normal human serum, with an upper limit of 265 Klett units or 75 lipase units, and with a mean of 155 Klett units or 43 lipase units. A survey of serum lipase in patients suspected of having pancreatitis was performed using a one hour and a five hour incubation method. Elevation of both lipase and amylase activity in serum correlated with the presence of early acute pancreatitis. Although correlation with amylase activity was closer, false positive amylaseactivity was detected in some patients by means of the lipase assay. Marked elevations in amylase were almost always accompanied by elevations in lipase. Although the five hour test is more reliable, the one hour test may serve as a useful adjunct in emergencies, since a positive one hour test consistently predicted a positive five hour test.