Cholesterol ratio: what total cholesterol to HDL tells you

Your cholesterol ratio is your total cholesterol divided by your HDL cholesterol. It weighs all the cholesterol in your blood against the share being carried back to the liver, in one number with no units. A lower ratio is generally better, and the ratio is one of the inputs to QRISK3, the heart risk calculator NICE recommends in the UK.

What the cholesterol ratio measures

Total cholesterol rises with LDL and the other particles that can build plaque. HDL carries cholesterol away. The ratio captures both at once, so the same total cholesterol reads very differently with a high HDL than with a low one. A total cholesterol of 5.5 mmol/L with an HDL of 1.1 gives a ratio of 5.0; the same total with an HDL of 1.6 gives about 3.4.

The Prospective Studies Collaboration pooled 61 studies, and among the 150,000 participants with HDL measured, the total to HDL ratio was the strongest predictor of death from ischaemic heart disease of the simple HDL-based measures it tested: 40% more informative than non-HDL cholesterol and more than twice as informative as total cholesterol. In the 52-country INTERHEART study, the ApoB / ApoA1 ratio did better still, accounting for an estimated 54% of heart attack risk at population level against 32% for the cholesterol ratio.

Cholesterol ratio normal range

Because the ratio divides one cholesterol figure by another, it is the same whether your lab reports in mmol/L or mg/dL. There is no single agreed cut-off. A review of lipoprotein ratios summarised these levels:

Total cholesterol / HDL ratio	Men	Women
Higher risk, people without heart disease	above 5.0	above 4.5
Suggested target, people without heart disease	below 4.5	below 4.0
Suggested target, people with heart disease	below 3.5	below 3.0

European guidance adds a caution: ratios such as this one are useful for estimating risk, but not for diagnosis or as treatment targets, and each part of the ratio should also be read on its own. Ranges vary by laboratory, method, age and sex, so read your result against the range on your own report.

What a high ratio usually points to

A high ratio means total cholesterol is high, HDL is low, or both. It often travels with raised triglycerides: in the Quebec Cardiovascular Study, men with higher triglycerides had higher ratios, and higher ratios went with more features of insulin resistance, such as higher insulin, higher ApoB and smaller LDL particles. It is a risk marker, not a diagnosis.

A doctor will usually go back to the parts, total cholesterol, HDL, LDL and triglycerides, and often ApoB, and put the ratio into a risk calculator with age, blood pressure, smoking and diabetes status. Before referring anyone to a specialist, NICE advises ruling out common secondary causes of abnormal lipids, such as an underactive thyroid, uncontrolled diabetes, liver disease, nephrotic syndrome and heavy drinking.

What a low ratio usually points to

A low ratio is generally favourable. Two cautions apply. If it is low because HDL is very high, that is not automatically protective: the 2019 European guideline notes that risk appears to rise again at extremely high HDL. And a low ratio says nothing about lipoprotein(a), an inherited risk factor that needs its own test.

What moves the ratio

• Anything that moves its parts. It rises when total cholesterol goes up or HDL goes down.
• Meals. Total cholesterol falls by about 0.2 mmol/L at most after an ordinary meal and HDL barely changes, so the ratio hardly moves.
• Pregnancy. Both parts rise: total cholesterol by about 43% by the third trimester and HDL by about 25% in one cohort.
• Other conditions. An underactive thyroid, uncontrolled diabetes, liver disease and nephrotic syndrome can all disturb lipids.
• Two measurements. Because it is calculated, any error in either value carries into the ratio.

Preparing for the test

The ratio does not need fasting, since neither part changes much after a meal. In a panel that includes fasting glucose and fasting insulin, the sample is taken after a fast anyway. Water is allowed.

How Clare's panel handles the cholesterol ratio

In Clare's panel, the ratio is calculated by Clare from two lab results, total cholesterol and HDL cholesterol, by dividing one by the other:

Total Cholesterol / HDL Ratio = Total Cholesterol divided by HDL Cholesterol

Both values come from the same sample and the same units, so the ratio has no unit of its own. Clare calculates three related ratios from the same panel: LDL / HDL, Triglycerides / HDL and ApoB / ApoA1.

Why it matters in the UAE

A household survey of 824 Emirati adults in the Northern Emirates, with fasting samples taken in 2012 and 2013, found a low HDL in 42.5% of participants, more often in women (47.4%) than men (37.9%). Since HDL is the bottom half of this ratio, that matters here. The same study reported a high ratio in 72.3%, but it used a cut-off of 3.4, much stricter than the 4.5 to 5.0 in the table above, so that figure cannot be compared with a typical risk threshold.

Related tests

The ratio is built from Total Cholesterol and HDL Cholesterol, and sits beside the LDL / HDL Ratio and the ApoB / ApoA1 Ratio. For why counting particles can say more than counting cholesterol, read ApoB: the cholesterol number most UAE panels skip.

Why the ratio means more over time

Lipid tests are usually repeated every five years when results are normal, and more often with diabetes, high blood pressure or heart disease, or on cholesterol-lowering treatment. Because the ratio moves when either part moves, a change between two results is worth reading back to its source: a rising total, a falling HDL, or both. Risk calculators such as QRISK3 also give a different answer each time the ratio changes. Clare is opening with a waitlist at clare.health.