LDL Cholesterol: Normal Values and What a High LDL Means

LDL stands for low-density lipoprotein, a particle that carries cholesterol through the blood. The LDL cholesterol result tells you how much cholesterol sits inside all of those particles together. It is a measure of cargo, not of particle number; that number is better approximated by non-HDL cholesterol and apolipoprotein B.

What most people do not know is that LDL is rarely measured in a routine lipid panel. It is calculated. The classic Friedewald equation subtracts HDL from your total cholesterol and then subtracts the cholesterol sitting in the triglyceride-rich particles: LDL = total cholesterol minus HDL minus triglycerides divided by 2.2, with everything in mmol/l. That divisor of 2.2 is a fixed assumption about the ratio between triglycerides and VLDL cholesterol. The assumption is what makes a lipid panel cheap, and it is also the reason an LDL result can simply be wrong.

The equation fails in four predictable ways.

More accurate alternatives exist. The Martin-Hopkins method replaces the fixed divisor with a factor that varies with a person's own triglycerides and non-HDL. The Sampson-NIH equation holds up to roughly 9 mmol/l of triglycerides. There is also a direct LDL assay, which measures the cholesterol in LDL particles itself and therefore does not depend on triglycerides; direct assays are, however, less well standardised between manufacturers, so two laboratories can report different numbers for the same blood.

So always know which kind of number you are holding. A calculated LDL is no more reliable than the three values it was built from.

Of all the values in a lipid panel, LDL has the strongest causal link with atherosclerosis. Every LDL particle carries one apolipoprotein B, enters the artery wall and can lodge there. The more of those particles pass through over decades, the more plaque builds up. That is why lowering a raised LDL is the best-evidenced way to reduce the risk of a heart attack and a stroke.

The most important sentence on this page, however, is not about high or low but about for whom. The 3.0 mmol/l upper limit on your report is a reference interval: it describes what is common in the population. It is not a goal. Guidelines tie the goal to your risk.

The consequence is sharp. An LDL of 2.8 mmol/l sits neatly inside the reference interval on the printout, while that same 2.8 is clearly too high for someone who has had a heart attack. Conversely, an LDL of 3.2 in a thirty-year-old with no other risk factors leads to a very different conversation than in a sixty-year-old who smokes, has diabetes and has high blood pressure. Your risk category, built from age, blood pressure, smoking, diabetes, kidney function, family history and existing cardiovascular disease, is what decides what your number means. Above seventy, LDL lowering is not routinely started in people without cardiovascular disease.

A second situation deserves attention. A strongly raised LDL in someone who takes no lipid-lowering medication, particularly alongside early cardiovascular disease in close relatives, is a reason for a doctor to look into whether familial hypercholesterolaemia may be present. That inherited condition affects roughly 1 in 250 to 300 people and remains under-diagnosed in the Netherlands. A blood value does not make that diagnosis and cannot make it: the conversation belongs with your doctor, who also looks at your family and your history.

The sensible reading rule, then, is that a single LDL number without a risk profile says little. Place the result alongside your HDL, your triglycerides, your non-HDL cholesterol and your blood pressure, and assess it together with a doctor.

A lipid panel may now be drawn non-fasting. Total cholesterol, HDL, non-HDL and apolipoprotein B barely change after a meal. The exception is triglycerides: they rise after eating and peak roughly three to five hours later. Because the calculated LDL depends on triglycerides, that rise feeds through into your LDL result. If you want the cleanest possible picture of your LDL, fasting is still the safest choice. If a non-fasting triglyceride result comes back above roughly 4.5 mmol/l, have it repeated fasting before anyone draws a conclusion from it.

There are moments when you are better off not testing. After a heart attack, major surgery or a serious infection, total cholesterol and LDL fall for weeks. A lipid panel drawn then gives a flatteringly low picture of your habitual value, so wait a few weeks after recovery. During pregnancy, cholesterol and LDL rise physiologically and substantially; a pregnancy lipid panel cannot be interpreted and testing should wait until at least six to eight weeks after delivery.

If your LDL is unexpectedly high, the question of an underlying cause belongs before any conversation about your diet. An underactive thyroid is the classic and frequently missed cause, and a TSH measurement rules it out easily. Nephrotic syndrome, cholestasis, poorly controlled diabetes, heavy alcohol use, pregnancy and a range of medicines can also raise LDL, among them corticosteroids, oral oestrogen, isotretinoin, thiazide diuretics, some beta blockers and anabolic steroids.

Finally, allow for natural variation. Total cholesterol and LDL vary from day to day by roughly five to ten percent, triglycerides by twenty to twenty-five percent. A 0.2 mmol/l difference between two measurements is therefore not a trend. If you follow your values over time, have them done at the same laboratory.