Why does my report say my LDL is calculated?
On this page
Because most labs don’t measure LDL. They work it out from your total, HDL and triglycerides, often with a formula from 1972. It slips when triglycerides are high or LDL is low, so the 2026 US guideline now prefers two newer equations.
What we’d do
Use the calculated LDL, but know which formula made it. If your triglycerides are over 150 or your LDL is near 70, ask your lab whether it uses Martin/Hopkins or Sampson/NIH, and look at your non-HDL too, which needs no formula at all. When you’re close to a goal line, a few points decide which side you’re on.
The 1972 shortcut
Measuring LDL directly once meant spinning blood in a lab machine called an ultracentrifuge. In 1972 three NIH researchers, William Friedewald, Robert Levy and Donald Fredrickson, published a way around it. Their paper’s title says so: “without use of the preparative ultracentrifuge”.
The formula is LDL = total − HDL − triglycerides ÷ 5. The lab measures your total cholesterol, your HDL and your triglycerides. The ÷ 5 is a guess at how much cholesterol rides in the triglyceride-carrying particles, and whatever is left is called LDL.
It’s like assuming the drinks are always a fifth of a dinner bill. At most dinners that’s close enough. At a wine bar it’s way off.
Where the guess slips
In 2013 a Johns Hopkins team looked at 1,350,908 US panels where LDL had been measured directly. The real ratio of triglycerides to that cholesterol wasn’t a fixed 5. Its median was 5.2, the middle half ran from 4.5 to 6.0, and it shifted with the triglyceride and cholesterol levels.
The biggest errors came where LDL was low and triglycerides were high. When the 1972 formula said someone’s LDL was under 70, this is how often a direct measurement agreed.
| Triglycerides | 1972 formula | Martin/Hopkins |
|---|---|---|
| 100 to 149 | 79.9% | 94.3% |
| 150 to 199 | 61.3% | 92.4% |
| 200 to 399 | 40.3% | 84.0% |
At triglycerides of 400 or more, the guideline says the 1972 formula can’t be used at all.
What it looks like on a real panel
Take a total of 150, HDL of 35 and triglycerides of 250. The 1972 formula gives an LDL of 65. The NIH equation gives 74. One puts this person under the goal of 70 and the other puts them over it. With a total of 215, HDL of 38 and triglycerides of 240, the two give 129 and 134.
The newer equations
- Martin/Hopkins (2013) swaps the fixed 5 for a factor picked from a table of 180 cells by your triglycerides and non-HDL. Johns Hopkins dropped its patent application so any lab can use it for free.
- Sampson/NIH (2020) is one equation built from 8,656 NIH patients whose LDL was measured by the lab’s reference method, and it works up to triglycerides of 800.
In a comparison of 23 equations in 5,051,467 patients, Martin/Hopkins put 89.6% of LDL values in the right group, Sampson/NIH 86.3% and the 1972 formula 83.2%. The 2026 guideline now says either newer equation “is preferred” over the old one.
Which LDL is right? runs your numbers through the formulas side by side, and lets you slide your triglycerides up to watch them split apart.
6 sources
- Friedewald WT, Levy RI and Fredrickson DS, Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge, Clinical Chemistry, 1972pubmed.ncbi.nlm.nih.gov
- Martin SS and others, Comparison of a novel method vs the Friedewald equation for estimating low-density lipoprotein cholesterol levels from the standard lipid profile, JAMA, 2013pubmed.ncbi.nlm.nih.gov
- Sampson M and others, A new equation for calculation of low-density lipoprotein cholesterol in patients with normolipidemia and/or hypertriglyceridemia, JAMA Cardiology, 2020pubmed.ncbi.nlm.nih.gov
- Johns Hopkins Medicine, news release on a comparison of 23 LDL equations in 5,051,467 patients, EurekAlert, 2023eurekalert.org
- Blumenthal RS, Morris PB, Gaudino M and others, 2026 ACC/AHA guideline on the management of dyslipidemia, JACC, 2026doi.org
- The same guideline, full text, Circulation, 2026api.iscpcardio.org
