Lipid profile explained: LDL, HDL, triglycerides and whether to fast

What a lipid profile contains

A lipid profile, sometimes called a lipid panel or cholesterol test, measures fats that travel in the blood. Cholesterol and triglycerides cannot dissolve in blood on their own, so they are carried inside particles called lipoproteins. The report usually lists:

• Total cholesterol: all the cholesterol carried by the different lipoproteins added together.
• LDL cholesterol: carried by low-density lipoproteins. Often called “bad” cholesterol because a higher level is linked to fatty deposits in artery walls.
• HDL cholesterol: carried by high-density lipoproteins. Often called “good” cholesterol because higher levels are linked with lower heart risk, although the relationship is not as simple as the nickname suggests.
• Triglycerides: another type of fat, which rises after meals, with alcohol and with excess calorie intake.
• Non-HDL cholesterol and VLDL cholesterol on some reports, and sometimes ratios such as total cholesterol to HDL.

Cholesterol is not a poison. Your body needs it to build cell walls and hormones. The concern is having more of the artery-clogging kinds than is healthy for your particular level of risk.

Units: mg/dL and mmol/L

Indian laboratories almost always report lipids in milligrams per decilitre (mg/dL). Many other countries use millimoles per litre (mmol/L). The conversion factors are different for cholesterol and triglycerides because their molecules have different weights:

• Cholesterol (total, LDL, HDL, non-HDL): mg/dL ÷ 38.67 = mmol/L.
• Triglycerides: mg/dL ÷ 88.57 = mmol/L.

For example, a total cholesterol of 200 mg/dL is about 5.2 mmol/L, and triglycerides of 150 mg/dL are about 1.7 mmol/L. If you read advice from another country, check its unit before comparing the number with your own report. Our guide to units on Indian lab reports has more worked examples.

Typical printed ranges, and why they are only a starting point

Many laboratories print simple categories next to each result. A commonly used set is shown below. The exact limits and wording differ between laboratories and guidelines.

These printed ranges are population categories. They are not personal targets. Doctors increasingly set LDL goals according to a person’s overall cardiovascular risk: someone who has already had a heart attack, stroke or stent, or who has diabetes or kidney disease, is generally advised to aim for a much lower LDL than someone with no other risk factors. The same LDL of 130 mg/dL could therefore mean different things for two different people.

Risk is estimated from age, sex, blood pressure, smoking, diabetes, family history and other factors, which is why a lipid report alone cannot tell you whether treatment is needed.

Fasting or non-fasting?

For years, patients were told to fast for 9 to 12 hours before a cholesterol test. Current thinking is more relaxed. Total cholesterol, HDL and non-HDL cholesterol change very little after a normal meal, and major guidelines now accept non-fasting samples for routine assessment in many adults.

Triglycerides are the number that rises most after eating, and the calculated LDL depends on them. Fasting is therefore still commonly requested when:

• Triglycerides are known to be high, or a non-fasting result was very high.
• A doctor wants the most stable baseline before starting or changing treatment.
• The laboratory’s own instructions say to fast.

The practical advice is to follow the instructions that come with your test request. Fasting means no food or sugary drinks, but usually plain water is fine and encouraged, and you should take your regular medicines unless your doctor has said otherwise. Our source on fasting before blood tests is listed below. If you forgot and ate, tell the person taking the sample so it can be noted on the report.

How LDL is calculated

Many laboratories do not measure LDL directly. They calculate it with the Friedewald formula: LDL = total cholesterol − HDL − (triglycerides ÷ 5), with all values in mg/dL.

The formula becomes unreliable when triglycerides are very high, generally above about 400 mg/dL, and some laboratories use other formulas or a direct LDL measurement in that case. If you see two reports with slightly different LDL values from the same blood, differences in method are a likely reason.

Non-HDL cholesterol is simply total cholesterol minus HDL. It includes all the potentially artery-clogging particles and does not depend on fasting, which is why some guidelines like it as an additional target.

A worked example (example values)

Take these example results in mg/dL: total cholesterol 210, HDL 45 and triglycerides 150.

LDL by Friedewald = 210 − 45 − (150 ÷ 5) = 210 − 45 − 30 = 135 mg/dL. Non-HDL = 210 − 45 = 165 mg/dL.

In mmol/L these are total cholesterol 5.4, LDL 3.5, HDL 1.2 and triglycerides 1.7. Reading them as a doctor might: total cholesterol and LDL are above the commonly printed desirable categories, HDL is a little low if the person is a woman, and triglycerides are borderline. Whether that matters for this person depends on their age, blood pressure, diabetes status, smoking, family history and any previous heart problems. For a young non-smoker with no other risk, the doctor may advise lifestyle changes and a repeat test. For someone with diabetes and a previous stroke, the same report could prompt a firmer treatment plan.

Things that affect a lipid result

• Recent meals, especially fatty ones, and alcohol the evening before, which raise triglycerides.
• Acute illness, infection or recent surgery, which can lower cholesterol temporarily.
• Pregnancy, which raises cholesterol and triglycerides normally.
• Underactive thyroid, kidney or liver disease, and uncontrolled diabetes.
• Some medicines, including certain steroids, hormones and drugs for blood pressure or HIV.
• Intense exercise in the preceding day and a change in weight or diet over recent weeks.

Because of this natural variation, a single result that surprises you is worth repeating before drawing conclusions, particularly if you were unwell or had changed your routine.

Other lipid results you may see

Some reports include extra lines that are worth knowing about.

• VLDL cholesterol, usually calculated as triglycerides divided by 5. It is an estimate, not a separate measurement.
• Total cholesterol to HDL ratio, and LDL to HDL ratio. Some laboratories print these with their own cut-offs. Doctors tend to rely on the individual numbers and on overall risk, but a falling ratio over time can be a useful sign of progress.
• Apolipoprotein B (ApoB), which counts the number of artery-clogging particles, and lipoprotein(a), an inherited fat particle usually measured once in a lifetime. These are ordered when a doctor wants a finer picture, for example in people with a strong family history of early heart disease. Lipoprotein(a) results are reported in different units between laboratories, so the unit and the range printed on the report matter even more than usual.

If a report lists values you do not recognise, ask the laboratory or your doctor to explain them, rather than searching for a number and comparing it with an unrelated range.

Children, pregnancy and older adults

Lipid levels change through life. Children and teenagers have their own ranges, and cholesterol is usually tested in young people only when there is a family history or another reason. Cholesterol and triglycerides rise normally during pregnancy and return towards baseline afterwards, so a result taken in pregnancy is interpreted differently. In older adults, treatment decisions depend on general health and previous heart events as well as on the numbers. In each case the range on a standard adult report may not apply to you.

What to do and not do

Do keep each report together so your doctor can see the trend, and tell them about family members who developed heart disease early. Do ask what LDL goal is right for you.

Do not start, stop or change a cholesterol medicine on the strength of a number you have read about online, and do not rely on supplements that promise to lower cholesterol without discussing them with your doctor. Do not assume a normal lipid report means a healthy heart: it is one risk factor among several.

Questions worth asking your doctor

• What is my overall cardiovascular risk, and which number matters most for me?
• What LDL target are we aiming for?
• Do I need to fast for the next test?
• Could another condition or a medicine be affecting these results?
• When should I repeat the test?

Sources

• MedlinePlus: Cholesterol Levels — what the cholesterol tests measure and typical categories
• MedlinePlus: Triglycerides Test — triglycerides and heart risk
• MedlinePlus: Fasting for a Blood Test — when fasting is and is not needed
• American Heart Association: HDL, LDL cholesterol and triglycerides — what each number means
• NHS: High cholesterol — causes, tests and lifestyle advice

A note on this guide

This guide is general information about lipid reports. It is not medical advice and does not replace your doctor’s assessment of your heart risk. Never change a medicine because of a result you have read about.