ABSTRACT
Most clinical laboratories directly measure serum triglyceride, total cholesterol, and high- density lipoprotein cholesterol. They indirectly calculate low-density lipoprotein cholesterol value using the Friedewald equation. Although high serum triglyceride [>400 mg/dL or 4.52 mmol/L] devaluates low- density lipoprotein cholesterol calculation by using this formula, effects of low serum triglyceride [<100 mg/dL or 1.13 mmol/L] on its accuracy is less defined. Two hundred thirty serum samples were assayed during a one-year period. In 115 samples, the triglyceride level was below 100 mg/dL and in 115 samples from age- and sex-matched patients the triglyceride level was 150 - 350 mg/dL [1.69 - 3.95 mmol/L]. In both groups total cholesterol was above 250 mg/dL [6.46 mmol/L]. On each sample, total cholesterol, high-density lipoprotein cholesterol, and triglyceride were directly measured in duplicate and low-density lipoprotein cholesterol measured directly and calculated with Friedewald equation as well. Statistical analysis showed that when triglyceride is <100 mg/dL, calculated low- density lipoprotein cholesterol is significantly overestimated [average :12.17 mg/dL or 0.31 mmol/L], where as when triglyceride is between 150 and 300 mg/dL no significant difference between calculated and measured low-density lipoprotein cholesterol is observed. In patients with low serum triglyceride and undesirably high total cholesterol levels, Friedewald equation may overestimate low-density lipoprotein cholesterol concentration and it should be either directly assayed or be calculated by a modified Friedewald equation. Using linear regression modeling, we propose a modified equation