Authoritative Data Source & Methodology
Primary formulas:
- Friedewald (1972): widely used LDL-C estimate: \( \mathrm{LDL\text{-}C} = \mathrm{TC} - \mathrm{HDL\text{-}C} - \frac{\mathrm{TG}}{5} \) (mg/dL). Less accurate at high TG (≥400 mg/dL). Source: MSD Manuals clinical calculator; JCP/NCEP references. MSD, NHLBI ATP III.
- NIH Sampson (2020): improved accuracy at low LDL-C and high TG (valid up to ~800 mg/dL). Implemented by many labs. Equation: \( \mathrm{LDL\text{-}C} = \frac{\mathrm{TC}}{0.948} - \frac{\mathrm{HDL\text{-}C}}{0.971} - \left(\frac{\mathrm{TG}}{8.56} + \frac{\mathrm{TG}\times \mathrm{non\text{-}HDL\text{-}C}}{2140} - \frac{\mathrm{TG}^2}{16100}\right) - 9.44 \) (mg/dL). Sources: JAMA Cardiology 2020; Stanford Labs implementation note. JAMA Cardiol, Stanford Lab.
Unit conversions: For TC/LDL-C/HDL-C, \( \text{mmol/L} = \text{mg/dL} \times 0.02586\). For TG, \( \text{mmol/L} = \text{mg/dL} \times 0.01129\). Sources: Omni Calculator unit guide; WHO/others list the same factors. Reference.
Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da queste fonti.
The Formula Explained
Friedewald (mg/dL): \(\displaystyle \mathrm{LDL\text{-}C} = \mathrm{TC} - \mathrm{HDL\text{-}C} - \frac{\mathrm{TG}}{5}\).
NIH Sampson (mg/dL): \(\displaystyle \mathrm{LDL\text{-}C} = \frac{\mathrm{TC}}{0.948} - \frac{\mathrm{HDL\text{-}C}}{0.971} - \left(\frac{\mathrm{TG}}{8.56} + \frac{\mathrm{TG}\times (\mathrm{TC}-\mathrm{HDL\text{-}C})}{2140} - \frac{\mathrm{TG}^2}{16100}\right) - 9.44\).
Derived measures: \(\mathrm{non\text{-}HDL\text{-}C} = \mathrm{TC} - \mathrm{HDL\text{-}C}\), \(\mathrm{TC/HDL}\) ratio, \(\mathrm{TG/HDL}\) ratio.
Glossary of Inputs & Outputs
- Total Cholesterol (TC): Sum of cholesterol across lipoproteins.
- HDL-C: “Good” cholesterol; higher is generally protective.
- Triglycerides (TG): Blood fats; high values can reduce LDL-C calculation accuracy.
- LDL-C (calculated): “Bad” cholesterol estimate via selected equation.
- non-HDL-C: Atherogenic cholesterol (TC − HDL-C); often targeted when TG are high.
- TC/HDL & TG/HDL ratios: Contextual markers sometimes used in risk discussions.
How It Works: A Step-by-Step Example
Suppose a non-fasting lipid panel reports TC = 200 mg/dL, HDL-C = 50 mg/dL, TG = 150 mg/dL. Using NIH Sampson:
- Compute non-HDL-C = 200 − 50 = 150 mg/dL.
- Compute the bracket term \(B = \frac{150}{8.56} + \frac{150 \times 150}{2140} - \frac{150^2}{16100}\).
- Compute LDL-C \(= \frac{200}{0.948} - \frac{50}{0.971} - B - 9.44\).
- Convert to mmol/L by multiplying by 0.02586 (for TC/LDL/HDL). For TG, multiply mg/dL by 0.01129.
The calculator performs these steps instantly and displays both mg/dL and mmol/L.
Frequently Asked Questions
Which method should I prefer?
Use NIH Sampson by default—especially if LDL-C is low or TG are elevated—because it is validated up to ~800 mg/dL TG and performs well in fasting or non-fasting samples.
When is Friedewald acceptable?
When TG < 400 mg/dL and conditions are typical (often fasting). It’s simpler and historically common, but can underestimate LDL-C when TG are high.
What are standard adult cutoffs?
TC: desirable <200 mg/dL; LDL-C: optimal <100 mg/dL; HDL-C: protective ≥60 mg/dL; low HDL-C: <40 mg/dL (men), <50 mg/dL (women). Discuss targets with your clinician.
Do I need to fast?
Not necessarily. Many guidelines permit non-fasting. If TG are very high, a fasting repeat can help; the NIH Sampson equation mitigates some inaccuracy.
What if TG > 800 mg/dL?
Calculated LDL-C is typically not reported; a direct LDL-C or apoB may be more appropriate.
Is this a diagnosis?
No—calculations support, not replace, clinical judgement. Always consult a healthcare professional.
Tool developed by Ugo Candido. Content verified by CalcDomain Editorial Board.
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