Determination of apolipoprotein A-I by kinetic nephelometry

Apolipoprotein A-I concentration in human serum was determined by kinetic nephelometry. Under optimal reaction conditions and within the normal physiological range the relation between apolipoprotein A-I concentration and measured rate units it approximately linear. The detection limit of the assay lies at 2 micrograms/ml. The coefficient of variation within one series is 1.44%. The correlation coefficient with alpha-cholesterol, as determined by agarose electrophoresis followed by polyanion precipitation, is better than 0.94. Addition of detergent to serum dilutions increases the reaction rate, suggesting that delipidation changes the antigenic expression of apolipoprotein A-I. The magnitude of this change is constant in normal controls, but not in special pathological cases. The described technique can be recommended for routine use in clinical chemistry for measurement of apolipoprotein A-I.