Clinical Chemistry, Vol 18, 845-849, Copyright © 1972 by the American Association for Clinical Chemistry

Nonlinear Regression Analysis Approach for Determining "True" Lactate Dehydrogenase Activity in Serum with the Centrifugal Analyzer ("Rotochem")

¹ Clinical Chemistry Service, Clinical Pathology Department, Clinical Center, National Institutes of Health, Bethesda, Md. 20014; and the Clinical Chemistry Laboratory, Hyland Laboratories, 3300 Hyland Ave., Costa Mesa, Calif. 92626.

Kinetic analyses for LD have been performed by use of a centrifugal analyzer. These analyses were performed on clinical control sera and human sera at 340 nm and 30°C. Evaluation of the data with both linear and nonlinear equations demonstrates that the exponential equation (y = C — Ae^bx) gives a lower value for "root mean square" (better fit) for the activity at high levels than does the linear equation (y = Ax + B). Assays done on a series of diluted sera demonstrate that a nonlinear equation approach gives a better estimate of enzyme activity than does the linear equation. The linear equation and four nonlinear functions are compared at various concentrations of NADH. The optimum concentration of NADH was found to be 0.226 mmol/liter. The best result was determined with the exponential equation.