Key result
Friedewald equation underestimates LDL-C at high triglycerides, misclassifying ~58% of patients to lower risk.
Why the study?
The Friedewald equation underestimates LDL-C levels at high serum triglyceride concentrations, affecting accurate dyslipidemia categorization.
Does the Friedewald equation accurately estimate LDL-C and correctly classify dyslipidemia risk compared to direct measurement across different triglyceride levels?
Cross-Sectional (n=1,288)
No
Does the Friedewald equation accurately estimate LDL-C and correctly classify dyslipidemia risk compared to direct measurement across different triglyceride levels?
The Friedewald equation substantially underestimates LDL-C when triglycerides exceed 250 mg/dL, misclassifying more than half of these patients into lower risk categories and potentially undertreating their cardiovascular risk.
Answers are grounded in this paper and cite their sources.
May warrant caution with Friedewald LDL-C at TG >250 mg/dL; extends bias observations but leaves open prospective outcome validation.
Background: In biochemical laboratories, low-density lipoprotein cholesterol (LDL-C) levels are generally measured using the widely accepted Friedewald equation:, where TC represents total cholesterol, and HDL stands for high-density lipoprotein.In the case of high serum triglycerides (TGs), the LDL-C value is underestimated using the Friedewald equation.Our study aimed to assess the reliability of calculated LDL-C (cLDL-C) compared with directly measured LDL-C (dLDL-C) in categorizing dyslipidemia patients across different TG levels.Methods: cLDL-C was estimated using the Friedewald equation, and dLDL-C was measured by the homogeneous method.Bland-Altman plots (BAPs) were plotted to analyze the agreement between dLDL-C and cLDL-C.We used Lind's concordance correlation coefficient to evaluate the correlation between stroke volume and cardiac output between the two methods.Mean bias with standard deviation and 95% confidence interval was determined at different TG strata.Results: BAP between dLDL-C and cLDL across TG levels also showed unacceptable agreement at higher TG levels.Mean bias between cLDL-C and dLDL-C is low; however, it rises to +20.2 mg/dL (-17.0 to 57.5) at 250-300 and +26.5 mg/dL (-17.7 to 70.6) above 300 mg/dL.Whereas, beyond TG values >250 mg/dL, cLDL-C shows poor sensitivity.At high TG concentrations, 58.7% of samples at 250-300 mg/dL and 58.1% above 300 mg/dL are assigned to a lower LDL-C band by the Friedewald equation than by direct measurement.Conclusions: The Friedewald equation shows acceptable agreement with the homogeneous direct LDL-C assay used in this laboratory at lower TG concentrations and unacceptable agreement at higher concentrations.At high TG concentrations (>250 mg/dL), the Friedewald equation misassigns more than half of patients to a lower LDL-C band than the homogeneous direct measurement and puts them at risk for atherosclerosis.Therefore, we recommend estimating LDL-C using Friedewald equation when serum TG is less than 250 mg/dL; beyond these levels, LDL-C should be measured directly.
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Gupta et al. (2026) conducted a cross-sectional in Dyslipidemia (n=1,288). Friedewald equation vs. Direct homogeneous LDL-C measurement was evaluated on Mean bias between direct and calculated LDL-C at triglyceride levels of 250-300 mg/dL (MD 20.24 mg/dL, 95% CI 17.18-23.30). The Friedewald equation significantly underestimates LDL-C at high triglyceride levels (>250 mg/dL), misassigning 58% of patients to a lower risk category compared to direct measurement.
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