HDL Cholesterol: Normal Values and What a Low HDL Means

Cholesterol does not dissolve in blood. To travel around anyway, it sits packed inside small spheres with a protein layer around them, and those spheres are called lipoproteins. HDL is the smallest and densest type. When your blood is drawn, nobody counts how many HDL spheres you have: what gets measured is how much cholesterol is inside them. So you are reading the cargo, not the number of lorries.

That distinction immediately explains why the nicknames are so misleading. HDL is not a different, better kind of cholesterol than LDL. It is exactly the same molecule, just in a different type of packaging and heading in a different direction. LDL particles bring cholesterol out to your tissues and can get stuck in the artery wall. HDL particles collect it instead and take it to your liver, which disposes of it through the bile. Good and bad therefore refer to the direction of transport, not to the substance itself.

Your result is given in mmol/l. For HDL the lab prints no upper limit, only a lower one, and it is not the same for everyone: 1.0 mmol/l for men and 1.2 mmol/l for women. That is because the female hormone oestrogen pushes HDL up. Useful to know if you compare your result with your partner's: 1.1 mmol/l is normal in him and too low in her.

One thing you need to know alongside it, or you will misread your result. Your HDL moves inversely with your triglycerides, the fats in your blood. The more triglycerides floating around, the faster your HDL particles are cleared. A low HDL is therefore almost never a problem in itself: it is usually the trace of a triglyceride value that is too high.

You do not need to fast for HDL. Eating barely changes this value.

Almost everyone knows one sentence about HDL: it is the good cholesterol and the higher the better. Both halves of that sentence are wrong, and explaining that is the most useful thing this page can do.

Why "good" is skewed. HDL is called good because it removes cholesterol instead of depositing it. But a high HDL does not prove that the removal is happening well. The test measures the cargo in your HDL particles, not how hard they work. So you can have a fine HDL number while the particles themselves function poorly, and nothing shows you that.

Why "higher is better" does not hold. Researchers followed more than 116,000 Danes for years and looked at which HDL value went with the fewest deaths. That turned out to sit around 1.9 mmol/l in men and around 2.4 mmol/l in women. Above that, mortality went back up, not down. So the relationship is a U and not a straight line. An HDL of 3.5 is not a better result than an HDL of 1.8.

And the strongest evidence: raising HDL does not work. If a high HDL really protected you, a drug that raises HDL ought to prevent heart attacks. That has been tried several times with agents that lifted HDL by tens of percent, and the number of heart attacks stayed the same. With the first agent in that series, more people actually died. People who have carried a gene since birth that raises their HDL do not have fewer heart attacks either.

What does that mean for you? That your HDL is a thermometer and not a dial. A low HDL does not tell you that your HDL is the problem, but that something else is going on: abdominal fat, smoking, too little movement or triglycerides that are too high. Those things carry the risk, and those you can do something about.

If you want to know how your arteries are doing, look at your LDL, your non-HDL cholesterol or your ApoB. Those are the numbers your GP bases a treatment on. There is no target value for HDL, precisely because nobody has been able to show that raising it helps.

HDL is almost never drawn on its own. It belongs to a cholesterol test, together with total cholesterol, LDL and triglycerides. Those four together are what make your result readable, because separately they say little.

You do not need to fast. HDL barely changes after eating, usually by less than a tenth of an mmol/l. Your triglycerides are a different matter: they rise considerably after a meal, and because your LDL is calculated from the other values, a non-fasting result can distort your LDL. If you want the whole picture right in one go, get drawn fasting.

Wait a few weeks after flu, an operation or a hospital admission before testing. Your whole cholesterol profile dips temporarily then, which makes your result look better than your usual situation.

A cholesterol test makes sense if you want to know where you stand, if cardiovascular disease runs in your family, if you smoke or carry excess weight, if your blood pressure or blood sugar is raised, or if you want to see whether a change in your lifestyle has had an effect. In that last case, wait at least three months before testing again: any sooner and too little changes to see anything.

Below is what your HDL value does in different situations.

One result is a snapshot. Have an abnormal value repeated before drawing conclusions from it.