Specificity of the commonly used enzymatic assay for plasma cholesterol determination

Aim: To assess the specificity and sensitivity of the commonly used enzymatic colorimetric test for plasma cholesterol determination. Methods: Interference with an enzymatic method for cholesterol measurement by several non-cholesterol sterols (beta sitosterol, campesterol, stigmasterol, stigmastanol, desmosterol, and lathosterol) was assessed. Some of these compounds are present in plasma at higher than normal concentrations either in rare genetic disorders, such as phytosterolaemia, or after the consumption of phytosterol enriched foods. Results: The non-cholesterol sterols were detected by the assay in a linear manner. There was no competitive interference in the presence of cholesterol. Conclusions: The crossreactivity may affect the diagnosis and treatment of non-cholesterol dyslipidaemias, including phytosterolaemia and cerebrotendinous xanthomatosis. Similarly, changes in plasma lipid compositions after the consumption of phytosterol enriched foods cannot be specifically determined by this enzymatic assay. Until a more specific enzymatic assay is developed, alternative methods such as gas chromatography should be used to differentiate between cholesterol and non-cholesterol sterols.