Friedewald LDL Cholesterol: Clinical Guide

Overview

Estimates LDL cholesterol from total cholesterol, HDL cholesterol and triglycerides using the Friedewald equation.

Clinical Significance

The Friedewald estimate is widely used when triglycerides are below 400 mg/dL. It becomes less reliable with hypertriglyceridaemia, very low LDL-C, dysbetalipoproteinaemia or non-standard sampling conditions.

When to Use

• Estimate LDL-C when a standard lipid profile is available and direct LDL-C has not been measured.
• Use only when triglycerides are below 400 mg/dL.
• Apply the result within a current cardiovascular-risk and lipid-management pathway.

How It Is Calculated

• LDL-C = total cholesterol − HDL-C − triglycerides ÷ 5 (mg/dL).
• The calculator validates the required inputs before applying the equation and rounds only the displayed result.

Interpretation

• The Friedewald estimate is widely used when triglycerides are below 400 mg/dL. It becomes less reliable with hypertriglyceridaemia, very low LDL-C, dysbetalipoproteinaemia or non-standard sampling conditions.
• Review the component values and assumptions as well as the final result.

Worked Example

Enter clinically plausible values in the stated units. MedicalC applies: LDL-C = total cholesterol − HDL-C − triglycerides ÷ 5 (mg/dL). Review the displayed result against the source data and the relevant clinical pathway.

Patient Considerations

• Confirm that the patient and clinical setting match the population or physiologic assumptions behind the equation.
• Consider whether treatment, organ function, pregnancy, body composition, sampling conditions or acute illness materially alter interpretation.
• Use serial calculations only when methods and units remain comparable.

Limitations

• Do not calculate when triglycerides are 400 mg/dL or higher.
• Accuracy falls at low LDL-C and with marked triglyceride elevation.
• The equation is an estimate and does not replace direct measurement when clinically required.

Clinical Pearls

• Check whether the laboratory already reports a directly measured or newer calculated LDL-C.
• Use the same units for all lipid inputs.
• Non-HDL cholesterol remains available even when Friedewald LDL-C is invalid.

Common Mistakes

• Entering mmol/L values into an mg/dL equation.
• Using the equation when triglycerides are 400 mg/dL or higher.
• Interpreting LDL-C without overall cardiovascular risk.

Evidence Base

The implementation uses the published or established relationship: LDL-C = total cholesterol − HDL-C − triglycerides ÷ 5 (mg/dL). The cited source should be reviewed alongside current specialty guidance before clinical deployment.

References

1. Friedewald WT, Levy RI, Fredrickson DS. Estimation of LDL cholesterol without preparative ultracentrifugation. Clin Chem. 1972;18:499-502. — Primary publication, authoritative guideline or recognised clinical source supporting the calculation.