Factors Causing Disagreement between Measured and Calculated Low Density Lipoprotein-Cholesterol (LDL-C) in Clinical Laboratory Services

BACKGROUND: Since measured low density lipoprotein-cholesterol (LDL-C) has been available in clinical laboratories, there have been concern about the disagreement between measured and calculated LDL-C and the factors causing their disagreement.
MATERIAL AND METHODS: Serum lipid concentrations were collected from 1,339 medical records of patients admitted to hospital between 2013 and 2015. They were grouped by their total cholesterol (TC), triglycerides (TG), and high-density lipoprotein-cholesterol (HDL-C) concentrations and the agreement between measured and calculated LDL-C was statistically analyzed.
RESULTS: A strong relationship was found between measured and calculated LDL-C. Significantly disagreements between measured and calculated LDL-C were found in all groups in 2013 and 2014 when lipids were analyzed by Cobas C501. Disagreements found in groups of low TG and low HDL-C concentrations in 2015 were when lipids were analyzed by Abbott Architect ci8200. In groups of calculated LDL-C <1.81 mmol/L, around 80% had the measured LDL-C >1.81 mmol/L. Among various atherogenic indices, non-HDL-C showed the strongest relationship with LDL-C, while TC to HDL-C ratio showed the strongest agreement with the LDL-C.
CONCLUSIONS: The disagreement between measured and calculated LDL-C in a clinical laboratory seemed to depend on the analytical system used, and was probably associated with individual laboratory variations.

Keywords: Cholesterol, LDL, Coronary Disease, Lipoprotein, HDL