Comparison of Equations for the Calculation of LDL-Cholesterol in Familial Hypercholesterolemia: Data from Iranian Registry

OBJECTIVE
Low-density lipoprotein cholesterol is the mainstay of diagnosis, treatment, and follow-up of patients with familial hypercholesterolemia, the most prevalent autosomal dominant disorder among humans. Since the reference measurement method (ultracentrifugation) is time-consuming and expensive, many formulas emerged to calculate low-density lipoprotein cholesterol levels and are commonly used in laboratories.

METHODS
To compare the performance of 3 low-density lipoprotein cholesterol calculation equations with a direct method (enzymatic photometric assay), the lipid profiles of 1148 patients of the registry of familial hypercholesterolemia in Iran were analyzed retrospectively,
270 of which had a possible or definite familial hypercholesterolemia diagnosis according to Dutch criteria. While measured using the direct method, we calculated the low-density lipoprotein cholesterol levels using the Friedewald, Chen, and Anandaraja formulas.

RESULTS
Our results showed that all 3 formulas are highly correlated with the direct method, and the Chen formula showed the highest intra-class correlation coefficient among all (0.954 among all patients with hypercholesterolemia and 0.947 among the familial hypercholesterolemia population). In addition, the Chen formula was the most sensitive, and the Friedewald formula was the most specific formula using a low-density lipoprotein cholesterol cut-off of 100 in familial hypercholesterolemia patients.

CONCLUSION
Our findings encourage applying the Chen formula in addition to the Friedewald formula to make better clinical decisions for familial hypercholesterolemia patients.