Automated turbidimetry of amylase activity by use of a discrete kinetic analyzer

We adopted an automated turbidimetric rate method for determining amylase activity to the KA-150 Kinetic Analyzer. In the method, an insoluble amylopectin substrate is used with activity determined by the rate of decrease in turbidity. Run-to-run CV for 59 samples with activities up to 400 units (arbitrary amylase units per 100 ml of sample) was 2.8%. A comparison with a similar method, performed by nephelometry, for 104 sera, showed a correlation coefficient (r) of 0.992, with a slope of 1.02. In an additional comparison with an amyloclastic method, for 52 sera r was 0.997, with a slope of 1.01. Day-to-day precision for control sera with activities near the upper limit of normal (279 and 216 units) averaged 2.5% during two months. Measured and calculated activity were linearly related to well above the upper limit of normal (normal range, 60-200 arbitrary units), showing a deviation from linearity of about 10% at 450 units. Commercial reagents available for the Perkin-Elmer Model 91 Amylase Lipase Analyzer can be used with the KA-150.