Turbidimetric measurement of lipase activity--problems and some solutions.

We optimized a commercial turbidimetric method for lipase (EC 3.1.1.3) activity (Boehringer Mannheim Diagnostics) and overcame some of its deficiencies. Increasing the bile salt concentration to 35 mmol/L and the colipase concentration to 6 mg/L and using a continuous recording of the reaction-rate curve greatly improved the reaction kinetics, eliminated false results from increases in absorbance, reduced the lag phase, and increased the analytical sensitivity and accuracy. Differentiation of pancreatitis from nonpancreatitis sera by adding NaCl, 140 mmol/L, to the assay mixture to observe the degree of enzyme activation has important limitations. Sera from patients with pancreatitis and only slight or modest increases in lipase behave like sera from healthy individuals or from patients with nonpancreatic disease. The assay shows no interference by lipoprotein lipase and carboxyl esterase. Results compare well by this optimized method and by an optimized "pH-Stat" titrimetric method.