LDL Calculator (Friedewald Equation)

The LDL Calculator uses the Friedewald equation to estimate low-density lipoprotein cholesterol from a standard fasting lipid panel. LDL-C is the primary target for cardiovascular risk reduction per ACC/AHA and ESC/EAS guidelines. Since direct LDL measurement is more expensive and not universally available, the Friedewald estimation remains the global standard laboratory method for routine LDL-C reporting.

The Friedewald equation: LDL = Total Cholesterol - HDL - (Triglycerides/5). The TG/5 term estimates VLDL cholesterol, based on the observation that fasting VLDL cholesterol is approximately one-fifth of triglyceride concentration in mg/dL. This relationship holds when triglycerides are below 400 mg/dL; above this threshold, the formula becomes inaccurate and direct LDL measurement is necessary.

LDL classifications per ATP III and 2018 ACC/AHA guidelines: below 70 mg/dL is optimal for very high-risk patients (prior ASCVD, multiple major risk factors), below 100 mg/dL is optimal for most adults, 100-129 is near/above optimal, 130-159 is borderline high, 160-189 is high, and 190+ is very high warranting statin therapy regardless of other risk factors. Current guidelines emphasize percentage LDL reduction rather than specific targets for primary prevention.

The Martin-Hopkins equation provides improved accuracy at low LDL levels and triglycerides 150-400 mg/dL by using adjustable TG:VLDL-C ratios derived from a large population database, rather than the fixed 5:1 ratio. This newer method is increasingly adopted by clinical laboratories and is available in many automated chemistry analyzers.

Non-HDL cholesterol (TC - HDL) is also calculated, serving as a secondary treatment target. Non-HDL captures all atherogenic lipoproteins and does not require fasting, making it increasingly recognized as a complementary or even superior risk marker to LDL-C alone. The non-HDL target is generally 30 mg/dL above the corresponding LDL target.

All results should be interpreted alongside the 10-year ASCVD risk score, family history, inflammatory markers like hs-CRP, coronary artery calcium score, and other clinical factors to determine appropriate therapy intensity. Lipid-lowering therapy includes statins as first-line, with ezetimibe and PCSK9 inhibitors for patients not achieving adequate LDL reduction on maximally tolerated statin therapy.