Determination of free and esterified cholesterol by a kinetic method. II. Evaluation of the enzymic method which uses 2,2-azino-di(3-ethyl-benzthiazoline-6-sulfonate) (ABTS) as chromogen.

A simple kinetic method for the determination of free and esterified serum cholesterol based on the oxidation of 2,2'-azino-di(3-ethyl-benzthiazoline-6-sulfonate) (ABTS) by use of choilesterol esterase, cholesterol oxidase and peroxidase has already been reported. Here the method is statistically examined. The method is very sensitive and precise (C.V. below 5%). The standard curve is linear up to 25.9 mmol/l. Comparison with results by Abell's method gave a linear regression of Yx = 0.2025 + 1.0043X with a correlation coefficient (r) of 0.983. Comparison with the enzymic methods of Roeschlau et al., Trinder, and Allain et al. gave Yx = 0.2037 + 0.9549X (r = 0.975), Yx = 0.4777 +0.8857X (r = 0.958) and Yx = 0.244 + 0.932X (r = 0.970), respectively. The effects of haemoglobin and bilirubin were studied and normal ranges for the method were determined on 150 healthy mature subjects of both sexes between 20 and 45 years of age. They are 3.375 to 6.948 mmol/l for total cholesterol, and 0.7196 to 2.089 mmol/l for free cholesterol.