What Is LDL Cholesterol, and What Does Your Value Actually Say?

Your result does not show one cholesterol value but a list, and that list is where most of the confusion starts. Total cholesterol is all your cholesterol added together. HDL is the part that carries cholesterol away to your liver, often called the good cholesterol. LDL is the part that can build up in the artery wall, the bad cholesterol. Triglycerides are a different kind of fat in your blood, which reacts strongly to what you eat and drink. And non-HDL is your total cholesterol minus your HDL: everything unfavourable, in one number.

LDL stands for low-density lipoprotein. That is a small sphere with a protein layer around it, which carries cholesterol through your blood. The LDL value counts how much cholesterol sits inside all those spheres together, in millimoles per litre (mmol/l).

The LDL in that list is almost never actually measured. The lab works it out: it takes your total cholesterol, subtracts your HDL, and then subtracts part of your triglycerides. That saves money and usually works fine.

But it also means your LDL moves along with those other values. If you ate shortly before the blood draw, your triglycerides go up, and the sum becomes less accurate. If your triglycerides are genuinely high, above roughly 4.5 mmol/l, many labs stop filling in an LDL at all. So if there is no LDL on your result when you expected one, that is usually the reason: your triglycerides were too high to trust the sum.

That is why non-HDL cholesterol is so handy: it is simply your total cholesterol minus your HDL, with no complicated sum in between. So that number cannot go off the rails either.

An LDL of 3.4 tells you that you sit above the general target, and whether that is a problem for you cannot be read from that single number. That is not evasion, it is the whole point. The very same 3.4 is no problem at all for one person and a reason to act for another.

That is because the 3.0 mmol/l on this page is a general target from the NVKC, the Dutch society of clinical chemists. It is not a personal goal. Your GP only sets a personal target when there is a reason to treat, and that reason comes from your overall cardiovascular risk: your age, your blood pressure, whether you smoke, whether you have diabetes, how your kidneys work, and whether heart problems appeared early in your family. The range the lab puts on your result, 0 to 4.5 mmol/l in our case, is something else again: that is the lab's own convention.

The consequence is sometimes surprising. Someone who has already had a heart attack gets a target below 1.8 mmol/l from the Dutch GP guideline, up to and including age seventy. For that person an LDL of 2.8 is clearly too high, even though it sits neatly under 3.0. Someone at high risk, for example through diabetes with organ damage, gets a target below 2.6. And for a healthy thirty-year-old with no other risk factors the guideline names no target at all: lifestyle advice is enough there. The other way round, an LDL of 3.2 in that thirty-year-old is a very different conversation than in a sixty-year-old smoker with high blood pressure.

There is one line that applies to everyone. Above 5.0 mmol/l the same guideline advises checking whether an inherited lipid disorder plays a part, especially where heart problems appeared early in your family. That question goes to your GP.

Why does it matter at all? Because every LDL particle can enter the artery wall and stay there. The more particles that pass by over the years, the more builds up. Of everything on your result, LDL has the strongest link with that process, and lowering it is the best-supported way to reduce your risk.

So do not take fright at one number. Put it next to your HDL, your triglycerides, your total cholesterol and your blood pressure, and discuss the whole picture with your GP, who knows the rest of your story.

Do you need to fast? For the list as a whole you no longer have to. Your total cholesterol and HDL barely change after a meal. Your triglycerides do rise, and because your LDL is calculated from them, your LDL moves too. If you mainly want to look at your LDL, come in fasting. If you just want a picture of your cholesterol, non-fasting is fine.

There are moments when it is better to wait. After surgery, a heavy infection or a hospital stay, your cholesterol runs lower than normal for weeks. Your result then looks better than it is. Wait a few weeks after you have recovered.

If your LDL is unexpectedly high, the first question is not what you eat but whether something else is going on. An underactive thyroid is the classic cause that gets overlooked, and you rule it out with a TSH test. Poorly controlled diabetes, kidney problems and certain medicines can also push your LDL up.

And allow for ordinary variation. Two measurements can easily differ by five to ten percent with nothing having changed. A difference of 0.2 mmol/l is not a trend. If you measure regularly, keep going to the same lab, otherwise you are comparing methods instead of yourself.