A lipid panel reports four numbers. Understanding what each represents is the easy part.
The harder parts are the ones nobody mentions. Units differ by country and use two separate conversion factors. Fasting is no longer routinely required. And a fifth number can be calculated from what you already have — one that some guidance says should appear on every report.
What each number represents
Briefly, since this part is well covered elsewhere.
Total cholesterol — the whole amount carried in the blood, across all carriers.
LDL cholesterol — cholesterol on the carriers that deliver it to tissues. The primary target of lipid-lowering strategies.
HDL cholesterol — cholesterol on the carriers that bring it back. The one number where lower is the concern.
Triglycerides — a different class of fat altogether, used mainly for energy storage.
Three of these measure the same molecule on different carriers. The fourth measures something else entirely. That distinction matters more than it sounds, as the next section shows.
Two units, two conversion factors
If you’ve held lab reports from two countries, you’ve met this problem.
The United States reports lipids in mg/dL. Canada, the UK, most of Europe and Australia use mmol/L. Converting between them requires knowing the molecule’s molar mass — and cholesterol and triglycerides are not the same molecule.
- Cholesterol (total, LDL, HDL, non-HDL): molar mass ≈ 386.65 g/mol → factor 67
- Triglycerides: average molar mass ≈ 885.7 g/mol → factor 57
| Analyte | mg/dL → mmol/L | mmol/L → mg/dL |
| Total, LDL, HDL, non-HDL | ÷ 38.67 | × 38.67 |
| Triglycerides | ÷ 88.57 | × 88.57 |
[Table 1] Lipid unit conversion by analyte · Source: Standard Clinical Test Conversion Factors[1][2]
Applying the cholesterol factor to a triglyceride value understates it by more than half[2]. This is described as the single most common error in manual lipid conversion[1].
A worked example. A triglyceride reading of 150 mg/dL is 150 ÷ 88.57 = 1.69 mmol/L. Divide by 38.67 instead and you get 3.88 — a number that looks alarming and is simply wrong.
The good news: ratios are unit-free. A total-to-HDL ratio is the same figure regardless of which units produced it.
Fasting is no longer routinely required
This one changed while many of us weren’t looking.
In 2016 the European Atherosclerosis Society and the European Federation of Clinical Chemistry and Laboratory Medicine issued a joint consensus statement recommending routine use of non-fasting lipid profiles[3].
The reasoning was empirical. Comparing random non-fasting profiles against fasting ones, the maximum mean changes one to six hours after ordinary meals were[3]:
- Triglycerides +0.3 mmol/L (26 mg/dL)
- Total cholesterol −0.2 mmol/L (8 mg/dL)
- LDL cholesterol −0.2 mmol/L (8 mg/dL)
- Non-HDL cholesterol −0.2 mmol/L (8 mg/dL)
And HDL cholesterol, apolipoprotein A1, apolipoprotein B and lipoprotein(a) were not affected at all by fasting status[3].
The panel concluded these shifts are not clinically significant, and that non-fasting and fasting values vary similarly over time and are comparable for predicting cardiovascular disease[3]. Fasting is reserved for specific situations — for instance when non-fasting triglycerides exceed 5 mmol/L (440 mg/dL)[3].
NICE and the Joint British Societies had reached a similar position in 2014[4]. US guidance, including ATP III and the 2013 ACC/AHA cholesterol guidelines, had recommended fasting for initial screening while permitting non-fasting total, HDL and non-HDL measurement[4].
A bit more detail — on how reports flag values. Because the reference points shift slightly, EAS/EFLM specified separate flagging thresholds for non-fasting samples: triglycerides ≥2 mmol/L (175 mg/dL), total cholesterol ≥5 mmol/L (190 mg/dL), LDL ≥3 mmol/L (115 mg/dL), non-HDL ≥3.9 mmol/L (150 mg/dL), HDL ≤1 mmol/L (40 mg/dL)[3]. For fasting samples the triglyceride threshold is ≥1.7 mmol/L (150 mg/dL)[3]. If your report flags a value, it’s worth knowing which set of cut-points was applied.
Non-HDL: the fifth number
Here’s the one I’d overlooked.
Non-HDL cholesterol = total cholesterol − HDL cholesterol. No extra blood draw. No extra cost. It’s arithmetic on numbers you already have.
What it captures is everything *except* the protective fraction — all the atherogenic lipoproteins in a single figure, including remnant cholesterol.
The EAS/EFLM consensus is direct about its status: non-HDL cholesterol includes the assessment of remnant lipoprotein cholesterol and shall be reported in all standard lipid panels[5].
The 2019 ESC/EAS guidelines recommend that non-HDL and apolipoprotein B may be preferred for estimating cardiovascular risk in people with diabetes, metabolic syndrome, obesity, high triglycerides, or very low LDL[6].
That last group is the practical case. When triglycerides are elevated, the standard LDL calculation becomes unreliable — a problem we covered when looking at how LDL is derived. Non-HDL sidesteps it entirely, because it doesn’t depend on estimating anything.
If your report doesn’t list it, you can work it out in one subtraction.
If you’re in Korea
Two differences worth knowing.
Korean reports use mg/dL, the same as the United States rather than the mmol/L used across most of Europe, the UK, Canada and Australia. If you arrived from one of those countries, your numbers will look roughly 39 times larger for cholesterol — and about 89 times larger for triglycerides. Same blood, different scale.
Fasting is still standard practice here for diagnostic lipid testing. Korean guidance calls for 12 hours or more of fasting when the purpose is diagnosis, and diagnosis rests on at least two measurements taken with an interval between them. So the European “come as you are” approach doesn’t transfer directly. If you’re booked for a lipid panel in Korea, assume fasting unless told otherwise.
One more thing specific to reading a Korean report. The LDL figure may be calculated rather than measured directly — and in Korean populations the standard calculation runs meaningfully lower than direct measurement. If your LDL sits near a decision threshold, that’s worth raising rather than treating the printed number as final.
Closing
The four numbers are the simple part. What surrounds them is where confusion lives.
What surprised me most was non-HDL. A figure that requires no extra test, that some consensus guidance says belongs on every panel, and that many people have never heard of — sitting one subtraction away from numbers they already hold.
The unit issue is less interesting but more likely to cause alarm. Two factors, one commonly confused for the other, and an error of more than 100% waiting for anyone who guesses.
None of this replaces the conversation where results get interpreted. It does mean arriving at that conversation knowing which questions are worth asking.
At a Glance
- Total, LDL and HDL measure the same molecule on different carriers; triglycerides are a different class of fat
- Units split by country — mg/dL in the US and Korea, mmol/L across most of Europe, the UK, Canada and Australia
- Two conversion factors: 38.67 for cholesterol, 88.57 for triglycerides — using the wrong one understates triglycerides by more than half
- Ratios such as total-to-HDL are unit-free
- EAS/EFLM 2016 recommends routine non-fasting lipid profiles; post-meal changes are ≤0.3 mmol/L, and HDL, ApoA1, ApoB and Lp(a) are unaffected
- Fasting is reserved for specific cases, such as non-fasting triglycerides above 5 mmol/L (440 mg/dL)
- Non-HDL = total − HDL; EAS/EFLM says it shall be reported in all standard lipid panels
- Non-HDL is preferred for risk estimation when triglycerides are high or LDL is very low, since it doesn’t rely on estimation
※ This article explains how lipid reports are constructed and is for general information only. It does not replace medical diagnosis, interpretation or treatment. Target values depend on your individual cardiovascular risk. Please have results interpreted by a clinician, and do not start, stop or adjust medication or supplements based on a number you have read yourself.
References
- “Cholesterol Converter: mg/dL to mmol/L” (conversion factors by analyte and common conversion error), https://testresult.ai/calculator-cholesterol.html
- “Cholesterol Unit Converter — mg/dL to mmol/L” (molar mass basis for 38.67 and 88.57), https://calculover.com/health-fitness/clinical/cholesterol-unit-converter/
- 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”, European Heart Journal 2016, https://pubmed.ncbi.nlm.nih.gov/27122601/
- “Re-assessing the role of non-fasting lipids; a change in perspective”, PMC, https://pmc.ncbi.nlm.nih.gov/articles/PMC5124629/
- “Quantifying atherogenic lipoproteins for lipid-lowering strategies: consensus-based recommendations from EAS and EFLM”, Atherosclerosis, https://www.sciencedirect.com/science/article/abs/pii/S0021915019316235
- “Apolipoprotein B and non-HDL cholesterol reveal a high atherogenicity in individuals with type 2 diabetes and controlled LDL-cholesterol” (ESC/EAS guideline positions on non-HDL as risk estimator), PMC, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7275418/