Calibration of a turbidimetric assay of serum lipase activity

Serum lipase activity has been measured by the turbidimetric method of Shihabi and Bishop, using an olive oil suspension as substrate (Shihabi, Z.K. and Bishop, C. (1971) Clin. Chem. 17, 1150-1153). For this method we developed a new calibration procedure, which can be carried out with great precision. Moreover, the technique is simple and fast and therefore suitable for routine use in clinical chemical laboratories. The new calibration procedure consists of the continuous titration of fatty acids, liberated by lipase from the sample, under the same reaction conditions as those used in the turbidimetric assay. A close correlation has been found with the results from the method of Shihabi and Bishop, in which method calibration has been carried out by making use of the linear relationship between the olive oil concentration and the absorbance of the suspension. In our method, the numerical results are twice those obtained by the method of Shihabi and Bishop. A possible explanation for this phenomenon is given.