Comparison Between the Direct Method and Friedewald's Formula for the Determination of Low-Density Lipoprotein Cholesterol Serum Levels in Horses.
Authors: Ribeiro Rodrigo M, Ribeiro Debora da Silva Freitas, Cota Leticia Oliveira, Carvalho Armando Mattos, Gobesso Alexandre Augusto de Oliveira, Faleiros Rafael R
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Determining serum LDL cholesterol in horses has become increasingly important given emerging links between elevated LDL and equine metabolic syndrome, yet practitioners have relied on indirect calculation methods when direct measurement isn't available. Researchers compared enzymatic colorimetry (direct analysis) against Friedewald's formula—a long-established equation that estimates LDL from total cholesterol, HDL, and triglyceride measurements—across 260 equine blood samples, finding moderate positive correlation (r = 0.688, P < 0.001) but notably poor coefficient of determination (R² = 0.4893). Mean LDL values differed between methods (22.12 ± 10.34 mg/dL via direct analysis versus 19.94 ± 19.13 mg/dL via Friedewald), with the formula showing substantially greater variability. Whilst Friedewald's formula demonstrates statistical significance as a rough estimator of equine LDL concentrations, the 49% coefficient of determination indicates it explains less than half the variance, rendering it insufficient to replace enzymatic colorimetric testing when metabolic assessment is clinically indicated—a meaningful distinction for practitioners managing horses with suspected metabolic dysfunction.
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Practical Takeaways
- •For horses with suspected metabolic syndrome, request direct LDL measurement rather than Friedewald-calculated values to ensure diagnostic accuracy.
- •The Friedewald formula underestimates LDL in horses and produces more variable results; it should not be used as a substitute for enzymatic testing in clinical decision-making.
- •When evaluating equine lipid profiles, be aware that calculated versus measured LDL values may differ substantially and could affect metabolic disease assessment.
Key Findings
- •Direct enzymatic colorimetry LDL measurement yielded mean 22.12 (±10.34) mg/dL versus Friedewald formula result of 19.94 (±19.13) mg/dL in 260 horse samples.
- •Significant correlation between direct and calculated LDL methods (P < 0.001, r = 0.688), but coefficient of determination (R² = 0.4893) was insufficient for method equivalence.
- •Friedewald formula can estimate equine LDL concentration but cannot reliably replace enzymatic colorimetric direct measurement in clinical practice.
- •Higher variability in Friedewald-calculated results (SD ±19.13) compared to direct method (SD ±10.34) limits its clinical utility.