The accuracy in using modified Friedewald equation to calculate LDL from non-fast triglyceride: a pilot study.

BACKGROUND: Total cholesterol, HDL (high-density lipoprotein) and LDL (low-density lipoprotein) are important risk factors of coronary heart disease. It is costly to perform the LDL test for follow-up cardiovascular diseases (CVD) especially for Gold Card Holders (Thirty Bahts Universal Coverage). Hypertriglyceridemia is also important as it is associated with uncontrolled type 2 Diabetes mellitus, low HDL, and metabolic syndrome. Because the serum triglyceride level changes with time after meal consumption, blood test for triglyceride level should be taken after fasting 12 hours. However this causes hunger and inconvenience in many patients. OBJECTIVE: To find out the optimal time to take blood for triglyceride measurement and using it for calculation of LDL with the original Friedewald Formula and the new Modified Friedewald Formula. MATERIAL AND METHOD: Patients were asked the approximate time of last meal/eating, drinking soft drink, milk. Additionally, the time of blood drawn from the patients was recorded The blood samples were drawn as usual amounts and the tests were done as the physicians ordered If enough sera were left, it would be analyzed for lipid profiles. LDL was also calculated by using standard Friedewald equation (sfLDL) and Modified Friedewald equation (mfLDL = total cholesterol - HDL - 1/6 triglyceride). Comparison between direct measured LDL (dmLDL), sfLDL, and mfLDL with time interval of last food, drink intake was done. RESULTS: There were 999 serum tubes left to be analyzed for lipid profiles and 919 sera (92.0%) left having triglyceride less than 300 mg/dl. Of those, 381, 84, and 454 samples came after fasting (nothing per oral = NPO) approximately less than 8 hours (h), 8-11.9 h, and 12 h or more respectively with sfLDL to dmLDL +/- 10 mg, comparison of 64.0%, 65.5% and 68.3% respectively. In contrast, comparing mfLDL to dmLDL +/- 10 mg being of 82.7%, 83.3% and 84.8% from the same samples and time intervals respectively thus, statistical significant (p-value < 0.001, odd ratios (OR) 2.59- 2.68). If blood drawn regardless of time from last food intake with triglyceride less than 300 mg/dl and with the above condition mfLDL, it gave 83.8% related to dmLDL while sfLDL gave only 66.3% p < 0.0001 and OR = 2.63. CONCLUSION: The present pilot study showed 919 of 999 sera (92.0%) with serum triglyceride less than 300 mg/ dl, regardless of the time of the last food intake. The authors used the new Modified Friedewald equation to calculate that the LDL had 83.8% accuracy when compared to direct measured LDL +/- 10 mg. This equation is more accurate than the standard (original) Friedewald equation with OR of 2.63. The authors offer that to save the cost, the new Modified Friedewald equation should be used to calculate LDL. Then, direct LDL measurement could be reserved for patients with hypertriglyceridemia, in the treatment of LDL in high-risk CVD.

Comparative study of LDL-cholesterol levels in Thai patients by the direct method and using the Friedewald formula.

In this study, low-density lipoprotein cholesterol (LDL-C) levels by direct measurement and estimation using the Friedewald formula, were compared among 1,016 Thai patients. The study assessed blood samples from out-patients sent to the Clinical Chemistry Laboratory, Department of Clinical Pathology, Rajvithi Hospital, Ministry of Public Health, for measurement of total cholesterol (TC), LDL-C, high-density lipoprotein cholesterol (HDL-C) and triglyceride (TG) levels, January 2004-December 2005. Patients' ages ranged 8-89 years, 573 (56.4%) were females. Linear regression analysis showed the two methods had highly significant correlation coefficients (p<0.001). Upon comparing the two methods, at TG levels of 151-200 mg/dl, bias was 18.3 mg/dl; and for TG levels of 201-300 mg/dl, bias was lower at 11.4 mg/dl; for TG levels of 301-400 mg/dl, bias increased to 20.9 mg/dl. The direct assay meets currently established analytical performance targets and may be useful for the diagnosis and management of hyperlipidemic patients. The Friedewald formula did not give a homogeneous performance when estimating LDL-C levels in samples with different TG levels.

Is calculated LDL-C by using the new modified Friedewald equation better than the standard Friedewald equation?

The patients who have CHD or CHD risk equivalents should have LDL-C level less than 100 mg/dL because of the great reduction of risk for major coronary events. Direct measurement of LDL-C is the most accurate but is expensive. But with the practical use of the Friedewald equation for calculating LDL-C, the authors noticed that the accuracy declined with triglyceride level being higher than 300 mg/dL. The authors determined the correlation of direct measurement of LDL-C with calculation LDL-C from the Friedewald equation and postulated the new modified Friedewald equation for calculating LDL-C by using 1/6 triglyceride to minus. From a total of 1079 fasting serum samples analysis, and determining the correlation of LDL-C from the direct measurement (dm LDL) while calculating LDL-C from equations of the standard Friedewald (sf LDL), and the new modified Friedewald (mf LDL), by using 1/6 triglyceride to minus instead of 1/5 triglyceride, if triglyceride was over 200 mg/dL. The authors found an excellent correlation within 0 +/- 10% difference of dm LDL and sfLDL if triglyceride was less than 200 mg/dL, but sf LDL is less accurate when the triglyceride level is high, and mf LDL has better correlation with dm LDL within 0 +/- 10% that sf LDL vs mf LDL, 72.3% vs 91.6% (p = 0.0001), and 58.3% vs 83.3%, (p = 0.01) when the triglyceride level is 200-299, and 300-399 mg/dL respectively. It is shown that sf LDL has more underestimation than mf LDL when compared with dm LDL (more than 10 mg/dL) as 26.9% vs 2.5% (p < 0.0001) and 41.6% vs 5.6% (p = 0.0003 ) with triglyceride of 200-299, and 300-399 mg/dL respectively, although mf LDL showed overestimation of more than 10 mg/dL difference with dm LDL as sf LDL vs mf LDL of 0.8% vs 5.8% (p = 0.03), and 0.0% vs 11.1% (p=0.03) if the triglyceride is in the range of 200-299 and 300-399 mg/dL respectively, even with a triglyceride level of 400-499 mg/dL, mfLDL still has good correlation with dm LDL up to 75.0%. The authors conclude that the standard Friedewald equation is excellent for LDL calculation if triglyceride is less than 200 mg/dL, but the accuracy is declined when triglyceride is over 200 mg/dL, the authors offer a new modified Friedewald equation to calculate LDL-C if triglyceride is in the range of 200-499 mg/dL which has a better correlation with direct measured LDL-C. However this new modified Friedewald equation needs to be testified again especially with dyslipidemic patient sera.