Objective: Assess the reliability of LDL-C levels calculated from four formulas (Friedewald, Anandaraja and colleagues, Chen et al, and Vujovic et al) when compared to direct LDL-C measurement (dLDL-C) in DM with various triglycerides (TG) levels.

Material and Method: The present study included 2,967 fasting Thai diabetic patients with TG levels less than 400 mg/dl. The total cholesterol and TG levels were measured by enzymatic colorimetric assay. The high-density lipoprotein cholesterol and dLDL-C levels were measured by homogeneous enzymatic colorimetric assay. The calculated LDL-C (cLDL-C) from each formula was compared to dLDL-C. In addition, the degree of agreement between the methods was assessed.

Results: The mean and standard deviation (SD) of dLDL-C was 122.3 (37.1) mg/dl, the mean (SD) of cLDL-C from the formula of Friedewald (F-LDL-C), Anandaraja and colleagues, Chen et al, and Vujovic et al (Vu-LDL-C) were 115.2 (35.8), 120.8 (35.2), 116.6 (34.2), and 123.9 (37.4) mg/dl, respectively. In aspect of the accuracy defined as the percentage of dLDL-C minus the cLDL-C within -10 to 10 mg/dl; the accuracy of Vu-LDL-C were higher than the other cLDL-C in overall and the most of subgroups of TG levels, except in the subgroup of TG levels <100 mg/dl which the accuracy of F-LDL-C was the highest. The overall number of dLDL-C minus Vu-LDL-C within -10 to 10 mg/dl was 2,655 cases (89.5% with p<0.001). The Vu-LDL-C showed a little discordance with dLDL-C at the higher levels of TG. All cLDL-C had systematic differences from dLDL-C, while only Vu-LDL-C had no proportional difference. The Vu-LDL-C yielded the lowest mean of difference between dLDL-C and cLDL-C of -1.60 with SD of 6.31 mg/dl, while F-LDL-C yielded the highest value of 7.06 with SD of 7.91 mg/dl. The Vu-LDL-C had the narrowest range of 95% limits of agreement (-13.97 to 10.77 mg/dl) and the difference neither depended on the magnitude of LDL-C measurements nor had proportional error.

Conclusion: The modified Friedewald formula of Vujovic et al provided the most accuracy with acceptable degree of agreement in DM compared to those derived from the original Friedewald formula or the others. The interference caused by hypertriglyceridemia was obviously diminished; thus, the formula of Vujovic et al is more reliable than the others in DM if TG levels are range from under 400 mg/dl to 100 mg/dl.

Keywords: Low density lipoprotein cholesterol, LDL-C, Direct measurement of LDL-C, Calculated LDL-C, Friedewald formula, Modified Friedewald formula, Diabetes mellitus, DM