Biomarker 101: Total cholesterol

Total cholesterol is the number most people know, and the least informative one on a lipid panel.

What total cholesterol is

Cholesterol is a lipid — a fatty substance. Some is made by the liver and some comes from food. Despite its reputation it is essential: it forms part of every cell membrane and is a building block for hormones including testosterone and oestrogen, as well as vitamin D.

Total cholesterol is simply the sum of what is circulating, combining the different carrier types into a single figure.

Why the total is a blunt measure

The problem with adding things together is that it hides the composition.

LDL carries cholesterol from the liver out to the tissues. In excess it contributes to build-up in artery walls. HDL does the reverse trip, collecting cholesterol and returning it to the liver, which is why higher HDL is generally regarded favourably.

Both are counted in the total. So two people with identical totals can have opposite profiles — one with high LDL and low HDL, another with the reverse. The single figure cannot distinguish them, which is why clinicians read the breakdown rather than the sum.

Triglycerides

A lipid panel also reports triglycerides, a different type of fat that stores unused energy. They are not included in the total cholesterol figure but are read alongside it, and they matter more when they appear with high LDL or low HDL.

Ratios

Because composition matters more than the sum, the ratio of total cholesterol to HDL is often more useful than either figure alone. It captures in one number what the total obscures.

Why it's measured

Cholesterol contributes to cardiovascular risk assessment, alongside blood pressure, smoking status, age, family history and whether you have diabetes. It produces no symptoms whatsoever, so testing is the only way to know where you sit.

In Australia and New Zealand, cardiovascular risk is assessed using regionally validated calculators that combine these factors — cholesterol is an input to that assessment rather than the assessment itself.

What moves cholesterol

Diet plays a part, particularly the balance of saturated and unsaturated fats. Physical activity is associated with higher HDL, and body composition affects LDL and triglycerides.

But genetics matter more than many people expect. Familial hypercholesterolaemia produces high cholesterol regardless of lifestyle, and it is more common than generally assumed. Age also affects it — the liver clears cholesterol less efficiently over time — and levels often rise in women through menopause.

Thyroid conditions and diabetes both alter how the body handles cholesterol.

What total cholesterol won't tell you

• It hides the breakdown. The same total can describe very different profiles.
• It isn't a risk score. Cholesterol is one input among several.
• It doesn't count particles. That is what ApoB measures, and the two can disagree.
• One reading isn't a trend. Lipids move with diet, illness and season.

The bottom line

Total cholesterol is a starting figure rather than an answer. What matters is the balance underneath it — and since high cholesterol causes no symptoms, a test is the only way to see any of it.