LDL cholesterol: what it is, what it tells you and why we test it

LDL cholesterol, often called bad cholesterol, is the cholesterol your blood carries out to your tissues. When it stays high for years, it builds up in the walls of your arteries. It causes no symptoms: only a blood test shows it.

Why we test it

LDL particles carry cholesterol out to your tissues. When there are too many of them for years, they get into the walls of your arteries and form plaques. Over time the plaques can narrow the arteries and raise the risk of heart attack and stroke.

What matters is how high your LDL is and for how many years. That is why finding out early helps: there is more time to bring it down.

It causes no symptoms. Only a blood test shows it.

What it tells you, and what it does not

If it is high, more cholesterol can end up in the walls of your arteries. Your family’s genes and your diet are usually behind it, sometimes weight and too little movement.

But LDL measures the cholesterol being carried, not how many particles carry it. When triglycerides are high, ApoB, a test that counts the particles, tells you more.

And on its own it does not tell your whole risk: blood pressure, smoking, glucose and family history count too.

That is why it is read together with other tests:

• HDL cholesterol: Takes extra cholesterol back to the liver
• Triglycerides: When they are high, a calculated LDL is less precise
• ApoB: Counts the particles, not just the cholesterol
• Lipoprotein(a): An inherited risk that diet does not change

Normal LDL cholesterol levels by age

The lab decides what is normal. Many lab reports call an LDL below 115 mg/dL desirable; others use a slightly higher limit. Your own report may print different limits.

The limit on your report is the same for women and men, and it does not change with age. What changes with age is your risk, and LDL tends to rise: in women especially after menopause.

The right number for you depends on your risk for your heart and arteries: age, blood pressure, smoking, diabetes, family history. Your doctor sets it, and the higher the risk, the lower your LDL should be.

In the Rosa report you also see your optimal range and what to do to reach it or stay in it.

What your result means

Find the row for your result, in mg/dL. Which values should a doctor see? From 190 up, and below 12. Above 400, the same day.

• Below 12: Very low. Very rare. It usually comes from strong cholesterol medicines, more rarely from poor fat absorption or a genetic cause. Talk to a doctor, especially if you take no cholesterol medicines.
• 12 to 100: Normal. Within your report’s limits. For your arteries, lower is generally better. In the Rosa report you also see whether you are in your optimal range.
• Above 100, below 115: Near the limit. Still within the limits of many lab reports, but close to the line. In the Rosa report, from here your plan suggests what to change in your diet.
• 115 to under 190: High. Above the limit on many lab reports. Your family’s genes and your diet are usually behind it. Change what you eat and repeat the test after about three months. Your doctor weighs your risk.
• 190 to 400: Very high. It can be inherited high cholesterol, called familial hypercholesterolaemia. Talk to a doctor: the family is usually checked too.
• Above 400: Extremely high. Very rare. It can be a severe inherited form. See a doctor the same day.

If your LDL cholesterol is high or low

• High LDL cholesterol: Genes and diet are usually behind it. It can be brought down.
• Low LDL cholesterol: For your arteries it is usually a good thing. Below 12 is very rare and should be seen by a doctor.

How LDL cholesterol is calculated

Labs often do not measure LDL: they calculate it from three other results in the same blood test. The most common calculation is called the Friedewald formula.

In mg/dL it works like this: take your total cholesterol, subtract your HDL and subtract a fifth of your triglycerides. Your report often says whether LDL was calculated or measured directly (direct LDL).

The calculation is meant for a fasting blood test. After a meal it is a little less precise. With very high triglycerides it is not reliable: then LDL can be measured directly, and ApoB tells you more.

What can skew the result

A few things change the number for a while. It helps to know them before you read it.

• A low carb or keto diet: A very low carb diet, or a phase of losing weight quickly, can push it up for a while.
• Omega-3 supplements: They lower triglycerides, not LDL. Those rich in DHA, a type of omega-3, can raise it a little.
• Less movement than usual: A spell of moving less than usual can push it up.
• Pregnancy: In pregnancy all blood fats rise, and that is normal. Read the number with your obstetrician.

When to worry

Talk to a doctor if:

• Your LDL is 190 or more.
• It is below 12.
• It stays high after a few months of changes to what you eat.
• Someone in your family had a heart attack or stroke at a young age.
• It is above 400: see a doctor the same day.
• You have chest pain or pressure: call 112 or go to the emergency department.

With Rosa, an LDL of 190 or more, or below 12, is always flagged to a doctor; above 400, urgently.

Frequently asked questions

What should my LDL cholesterol be? It depends on your risk. Many lab reports call a number below 115 mg/dL desirable, but if your risk is higher your doctor may ask for a lower one. For your arteries, lower is generally better.

Do normal values change with age for women? The limit on your report does not: it is the same at every age, for women and men. But after menopause LDL often rises, and how low yours should be depends on your risk: your doctor decides.

Is there a table of values? Yes, it is the table higher up on this page. For each band it says what your number means and what to do. If your report uses different bands, its limit is the one that counts.

Do I need to fast for an LDL cholesterol test? It is better. If LDL is calculated, fasting makes the calculation more precise, and other tests in the same draw need fasting anyway. You can drink water.

How often should it be checked? For people who feel well there is no fixed rule: Rosa measures it twice a year. After a change in diet it is usually checked again after about three months, or when your doctor says so.

Sources

• Mach and colleagues, ESC/EAS guidelines for the management of dyslipidaemias: lipid modification to reduce cardiovascular risk. European Heart Journal, 2020. PMID 31504418
• Ference and colleagues, the evidence that LDL causes atherosclerotic cardiovascular disease, and that how long it stays high matters too. European Heart Journal, 2017. PMID 28444290
• Nordestgaard and colleagues, non-fasting lipid tests and the values a lab report should flag. European Heart Journal, 2016. PMID 27122601
• Friedewald and colleagues, estimating LDL cholesterol without measuring it directly. Clinical Chemistry, 1972. PMID 4337382
• Cuchel and colleagues, 2023 update of the consensus on homozygous familial hypercholesterolaemia, the most severe inherited form. European Heart Journal, 2023. PMID 37130090