Clinically relevant differences in LDL-c levels estimated by three different equations

Introduction and methods

Background and aim of the study

The most common means to estimate LDL-c is the Friedewald equation, which was developed in the 1970s from a relatively small sample of individuals [1]. However, the Friedewald equation has a reduced accuracy in patients with low LDL-c and high TG levels. To address this limitation, the Martin/Hopkins and Sampson equations were developed [2,3]. This study investigated the differences in estimated LDL-c using the Friedewald, Sampson, and Martin/Hopkins equations.

Methods

Electronic health record data were retrospectively analyzed. A total of 146,106 patients with clinical ASCVD and ≥1 lipid panel with a TG level <400 mg/dL were included. Mean age was 68 years, 56% were male and 91% were white. LDL-c was estimated in mg/dL using the Friedewald, Sampson, and Martin/Hopkins equations.

Concordance between the equations was assessed in three comparator groups (index equation vs comparator):

- Friedewald vs Sampson

- Friedewald vs Martin/Hopkins

- Sampson vs Martin/Hopkins

Patients were categorized as concordant if LDL-c was <70 mg/dL in both equations and discordant if LDL-c was <70 mg/dL for the index equation and ≥70 mg/dL for the comparator.

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Outcomes

Key outcomes included the rates of discordance between LDL-c equations at an LDL-c cutpoint of 70 mg/dL in all patients and in those with TG levels ≥150 mg/dL.

Other outcomes included the percentage of patients having >10-mg/dL LDL-c differences for comparisons between equations, the absolute magnitudes of discordance, and rates of discordance with other LDL-c cutpoints.

Main results

• Estimated LDL-c values were consistently higher with the Martin/Hopkins equation, compared with the Friedewald and Sampson equations.
• Discordance rates were 15% for the Friedewald vs Martin/Hopkins comparison (in other words, in 15% of cases the Friedewald equation estimated a LDL-c value <70 mg/dL, while the Martin/Hopkins equation estimated a LDL-c value ≥70 mg/dL.), 9% for the Friedewald vs Sampson comparison, and 7% for the Sampson vs Martin/Hopkins comparison.
• Discordance rates were higher in patients with TG ≥150 mg/dL (41%, 23%, and 23% for the Friedewald vs Martin/Hopkins, Friedewald vs Sampson and Sampson vs Martin/Hopkins, respectively).
• For the Friedewald and Martin/Hopkins comparison, >10-mg/dL differences in LDL-c were found in 48% of all patients and in 67% of patients with TG levels ≥150 mg/dL.
• The absolute magnitude of discordance in all patients with LDL-c <70 mg/dL by the Friedewald equation and ≥70 mg/dL by the Martin/Hopkins equation was 11.8 ± 7.5 (mean ± SD) mg/dL, and 14.8 ± 6.7 mg/dL in those with TG ≥150 mg/dL. The corresponding values for the Friedewald vs Sampson comparison were 6.3 ± 3.8 mg/dL and 8.2 ± 3.2 mg/dL, respectively.
• Discordance rates increased when a lower LDL-c cutpoint of 55 mg/dL was used: 23% for the Friedewald vs Martin/Hopkins comparison, 15% for the Friedewald vs Sampson comparison and 10% for the Sampson vs Martin/Hopkins comparison. The discordance rates for comparisons with a LDL-c cutpoint of 55 mg/dL in those with TG levels ≥150 mg/dL were 60%, 36% and 37%, respectively.

Conclusion

References

Find this article online at J Am Coll Cardiol.