35 Sitosterol is a Positive Interferent in the Roche Total Cholesterol and LDL-Cholesterol Assays

Sitosterolemia is an inherited disorder of plant sterol transport which may result in early cardiac death if untreated. The medical literature is littered with case reports of sitosterolemia misdiagnosed as familial hypercholesterolemia. These diagnostic errors were most likely due to the similar presentation of these two inherited conditions. Specifically, both lipid disorders may present with xanthomas and elevated “cholesterol” on routine lab work. The objective of this study was, therefore, to determine if sitosterol is an interferent in the Roche lipid panel; specifically, this panel includes Total Cholesterol, LDL-Cholesterol, HDL-Cholesterol, and Triglycerides. To test this hypothesis, we selected patient samples that covered the analytical measurement range and spiked them with increasing concentrations of sitosterol. In all cases, regardless of the starting concentration in the patient samples, Total Cholesterol and LDL-Cholesterol increased in a linear, dose-dependent manner. There was nearly a 1mg/dL increase in Total Cholesterol and LDL-Cholesterol for every 1 mg/dL sitosterol. The correlation was excellent (R-squared = 0.97-0.99). This same relationship was not observed in the assays for HDL-Cholesterol and Triglycerides. In conclusion, these results show that sitosterol should be included as an interferent in the package insert for the Roche Total Cholesterol and LDL-Cholesterol assays. Furthermore, if there is suspicion of sitosterolemia, clinicians need to be aware that gas or liquid chromatography are required for definitive quantitation of phytosterols.