The essentials

On most lab reports, LDL cholesterol is not measured but calculated from total cholesterol, HDL and triglycerides. The classic Friedewald formula becomes unreliable when triglycerides are high or LDL is very low. Newer formulas (Martin-Hopkins, Sampson-NIH) and direct LDL tests do better, so check which method your report names before comparing results.

How do I read a calculated LDL line on my report?

In this fictitious lipid panel, "calculated" next to LDL means the number comes from a formula[1].

Fictitious example of a lab report line (United States format)
TestResultReference rangeFlag
Cholesterol, total212 mg/dL<200 mg/dLH
HDL cholesterol46 mg/dL>=40 mg/dL-
Triglycerides180 mg/dL<150 mg/dLH
LDL cholesterol, calculated (Friedewald)130 mg/dL<100 mg/dLH
Non-HDL cholesterol166 mg/dL<130 mg/dLH
  1. Total cholesterol, HDL and triglycerides are measured; they feed the formula.
  2. LDL 130 mg/dL, calculated: 212 − 46 − 36 (180 ÷ 5) = 130, the Friedewald formula[3][6].
  3. Non-HDL cholesterol: total cholesterol minus HDL. It needs no triglyceride estimate.
  4. Reference range: under 100 mg/dL is the healthy adult level given by MedlinePlus[1]; your doctor may set another goal.

Not sure which method your lab used, or why your LDL changed? BloodSense reads your complete lipid panel line by line and helps you prepare your questions for the visit.

Get my lipid panel explained

Why is LDL calculated instead of measured?

The reference method for LDL needs ultracentrifugation, which routine labs do not use[7]. In 1972, Friedewald and colleagues showed that LDL could be estimated from the three values of a standard lipid panel[3]. In a fasting sample, cholesterol sits on HDL, LDL and VLDL particles. Subtract HDL and an estimate of VLDL from the total, and what is left is LDL[6].

It needs no extra test, so most labs still use a formula[6]. What the number means for your heart is covered in our guide to LDL cholesterol levels; this page explains how it is produced.

What is the Friedewald formula for LDL?

In mg/dL: LDL = total cholesterol − HDL − (triglycerides ÷ 5)[3][6].

"Triglycerides ÷ 5" estimates the cholesterol in VLDL, assuming a fixed ratio of 5[4]. More on this particle in our non-HDL and VLDL guide.

But the real ratio varies: in 1.35 million US lipid profiles, its median was 5.2 with wide spread[4]. The estimate drifts above about 250 mg/dL of triglycerides, and the formula is not recommended above 400 mg/dL[6].

What are the Martin-Hopkins and Sampson (NIH) equations?

The main ways a lab gets your LDL number
MethodHow it worksUsable up to (triglycerides)
Friedewald (1972)Fixed factor: triglycerides divided by 5400 mg/dL[6]
Martin-Hopkins (2013)Adjustable factor from a 180-cell table (triglycerides and non-HDL)400 mg/dL; an extended version goes to about 800 mg/dL[7]
Sampson-NIH (2020)Equation using triglycerides and non-HDL, built on reference measurements including high triglycerides800 mg/dL[5]
Direct LDLMeasured by the analyzerNo formula limit; results vary between brands[6][7]

Martin-Hopkins matches the factor to your own values. Below 400 mg/dL of triglycerides, it placed people in the same LDL category as direct measurement in 91.7% of cases, against 85.4% for Friedewald[4].

Sampson-NIH, developed at the US National Institutes of Health, was more accurate than both older formulas against the reference method, with 35% fewer misclassifications at triglycerides of 400 to 800 mg/dL[5].

When is calculated LDL not accurate?

  • Common High triglycerides. About one third of adults have triglycerides above 150 mg/dL[6]. Above 400 mg/dL, Friedewald should not be used: some labs then switch to a direct LDL test[6], others leave LDL blank with a comment.
  • Common Very low LDL, often on treatment. Below 70 mg/dL, Friedewald tends to read too low[6]. With triglycerides of 200 to 399 mg/dL, a Friedewald LDL under 70 was truly under 70 in only 40.3% of cases, against 84.0% with Martin-Hopkins[4]. This matters because the 2026 US guideline sets a goal below 55 mg/dL for very high-risk heart patients[9].
  • Possible A sample taken after a meal. After usual meals, triglycerides rise by up to about 26 mg/dL and calculated LDL falls by up to about 8 mg/dL[8]. Small, but enough to cross a cut-off.
  • Rare Unusual inherited lipid disorders, where both the formulas and some direct tests can be inaccurate[6][7].

Direct LDL tests are not perfect either: they are not fully standardized between manufacturers and can be inaccurate with abnormal lipids[6][7]. Doctors may also look at apolipoprotein B or non-HDL cholesterol, which need no triglyceride formula.

What is a normal calculated LDL?

The method changes how the number is obtained, not the cut-offs.

Examples of LDL cut-offs for adults (your laboratory's range prevails)
SourceValueSame value in mmol/L
MedlinePlus, healthy level for adults 20 and older[1]Less than 100 mg/dLLess than 2.59 mmol/L
MedlinePlus, healthy level up to age 19[1]Less than 110 mg/dLLess than 2.84 mmol/L
Possible inherited high cholesterol (European consensus)[8]Above 190 mg/dLAbove 5 mmol/L

To convert, divide mg/dL by 38.67. Personal goals depend on your overall risk: see high cholesterol.

Should I fast before a cholesterol test?

  • Ask whether you need to fast: 9 to 12 hours when required, though many people can be tested without fasting[1][8]. See fasting before a blood test.
  • If your triglycerides run high, a fasting sample is more reliable; a European consensus suggests one when non-fasting triglycerides exceed 440 mg/dL[8].
  • Note the method on your report: Friedewald, Martin-Hopkins, NIH (Sampson) or direct.
  • Use the same laboratory for follow-up, and keep taking your medicines unless told otherwise.

When should I see a doctor about my LDL result?

When to see a doctor

  • Emergency: call 911 for chest pain, sudden breathlessness, one-sided weakness, trouble speaking or a drooping face.
  • Within a few days if triglycerides are above 880 mg/dL (pancreatitis risk) or LDL is above 190 mg/dL[8].
  • At your next appointment for an LDL flagged high, left blank, or changed after a switch of laboratory.

Questions to ask your doctor

  1. Which method did the lab use for my LDL, and does it matter for me?
  2. Are my triglycerides high enough to make the calculated LDL less reliable?
  3. Should my next test be fasting, a direct LDL, or an apoB test?
  4. What LDL goal do you want me to reach, and why?

Frequently asked questions

Is calculated LDL the same as direct LDL?

They aim at the same thing, one estimated and one measured. They are usually close but can differ when triglycerides are high or LDL is very low[6].

Why is my LDL blank on the report?

Usually because triglycerides were too high for the formula (above 400 mg/dL with Friedewald). A direct LDL test can then be done[6].

Can I calculate my LDL myself?

For Friedewald, yes, using mg/dL values. Martin-Hopkins and Sampson need a table or longer equation. Your doctor goes by the lab's value.

Why did my LDL change when I switched labs?

Labs may use different formulas or direct assays, which are not fully standardized[7]. A small change can come from the method, not your body.

I take a statin. Is my calculated LDL still reliable?

Treatment can bring LDL very low, where Friedewald tends to underestimate. Newer equations or a direct test are more accurate there[5][6].

  1. MedlinePlus. Cholesterol levels. US National Library of Medicine. medlineplus.gov (accessed October 29, 2026)
  2. Centers for Disease Control and Prevention. Testing for cholesterol. Reviewed May 15, 2024. cdc.gov (accessed October 29, 2026)
  3. Friedewald WT, Levy RI, Fredrickson DS. Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin Chem. 1972;18(6):499-502. PMID 4337382 (accessed October 29, 2026)
  4. Martin SS, Blaha MJ, Elshazly MB, et al. Comparison of a novel method vs the Friedewald equation for estimating low-density lipoprotein cholesterol levels from the standard lipid profile. JAMA. 2013;310(19):2061-2068. doi:10.1001/jama.2013.280532 (accessed October 29, 2026)
  5. Sampson M, Ling C, Sun Q, et al. A new equation for calculation of low-density lipoprotein cholesterol in patients with normolipidemia and/or hypertriglyceridemia. JAMA Cardiol. 2020;5(5):540-548. doi:10.1001/jamacardio.2020.0013 (accessed October 29, 2026)
  6. Wolska A, Remaley AT. Measuring LDL-cholesterol: what is the best way to do it? Curr Opin Cardiol. 2020;35(4):405-411. doi:10.1097/HCO.0000000000000740 (accessed October 29, 2026)
  7. Martins J, Steyn N, Rossouw HM, Pillay TS. Best practice for LDL-cholesterol: when and how to calculate. J Clin Pathol. 2023;76(3):145-152. doi:10.1136/jcp-2022-208480 (accessed October 29, 2026)
  8. Nordestgaard BG, Langsted A, Mora S, et al. Fasting is not routinely required for determination of a lipid profile: a joint consensus statement from the European Atherosclerosis Society and European Federation of Clinical Chemistry and Laboratory Medicine. Eur Heart J. 2016;37(25):1944-1958. doi:10.1093/eurheartj/ehw152 (accessed October 29, 2026)
  9. Siddiqi AK, Jacob J, Khan MS, Kulkarni A. Top 10 concepts in secondary ASCVD prevention from the 2026 ACC/AHA dyslipidemia guideline: what is new and why it matters. Curr Atheroscler Rep. 2026;28(1). doi:10.1007/s11883-026-01465-5 (accessed October 29, 2026)
  10. Medicare.gov. Cardiovascular disease screenings. Centers for Medicare & Medicaid Services. medicare.gov (accessed October 29, 2026)

This page is general information. It does not replace the advice of a doctor, who interprets your results with your symptoms, history and examination.