What is a blood cholesterol ratio? And what should yours be?

Have you had a blood test to check your cholesterol level? These check the different blood fat components:

• total cholesterol
• LDL (low-density lipoprotein), which is sometimes called “bad cholesterol”
• HDL (high-density lipoprotein), which is sometimes called “good cholesterol”
• triglycerides.

Your clinician then compares your test results to normal ranges – and may use ratios to compare different types of cholesterol.

High blood cholesterol is a major risk factor for cardiovascular disease. This is a broad term that includes disease of blood vessels throughout the body, arteries in the heart (known as coronary heart disease), heart failure, heart valve conditions, arrhythmia and stroke.

So what does cholesterol do? And what does it mean to have a healthy cholesterol ratio?

What are blood fats?

Cholesterol is a waxy type of fat made in the liver and gut, with a small amount of pre-formed cholesterol coming from food.

Cholesterol is found in all cell membranes, contributing to their structure and function. Your body uses cholesterol to make vitamin D, bile acid, and hormones, including oestrogen, testosterone, cortisol and aldosterone.

When there is too much cholesterol in your blood, it gets deposited into artery walls, making them hard and narrow. This process is called atherosclerosis.

Cholesterol is packaged with triglycerides (the most common type of fat in the body) and specific “apo” proteins into “lipo-proteins” as a package called “very-low-density” lipoproteins (VLDLs).

These are transported via the blood to body tissue in a form called low-density lipoprotein (LDL) cholesterol.

Excess cholesterol can be transported back to the liver by high-density lipoprotein, the HDL, for removal from circulation.

Another less talked about blood fat is Lipoprotein-a, or Lp(a). This is determined by your genetics and not influenced by lifestyle factors. About one in five (20%) of Australians are carriers.

Having a high Lp(a) level is an independent cardiovascular disease risk factor.

Knowing your numbers

Your blood fat levels are affected by both modifiable factors:

• dietary intake
• physical activity
• alcohol
• smoking
• weight status.

And non-modifiable factors:

Read more: Got high cholesterol? Here are five foods to eat and avoid

What are cholesterol ratios?

Cholesterol ratios are sometimes used to provide more detail on the balance between different types of blood fats and to evaluate risk of developing heart disease.

Commonly used ratios include:

1. Total cholesterol to HDL ratio

This ratio is used in Australia to assess risk of heart disease. It’s calculated by dividing your total cholesterol number by your HDL (good) cholesterol number.

A higher ratio (greater than 5) is associated with a higher risk of heart disease, whereas a lower ratio is associated with a lower risk of heart disease.

A study of 32,000 Americans over eight years found adults who had either very high, or very low, total cholesterol/HDL ratios were at 26% and 18% greater risk of death from any cause during the study period.

Those with a ratio of greater than 4.2 had a 13% higher risk of death from heart disease than those with a ratio lower than 4.2.

2. Non-HDL cholesterol to HDL cholesterol ratio (NHHR)

Non-HDL cholesterol is the total cholesterol minus HDL. Non-HDL cholesterol includes all blood fats such as LDL, triglycerides, Lp(a) and others. This ratio is abbreviated as NHHR.

This ratio has been used more recently because it compares the ratio of “bad” blood fats that can contribute to atherosclerosis (hardening and narrowing of the arteries) to “good” or anti-atherogenic blood fats (HDL).

Non-HDL cholesterol is a stronger predictor of cardiovascular disease risk than LDL alone, while HDL is associated with lower cardiovascular disease risk.

Because this ratio removes the “good” cholesterol from the non-HDL part of the ratio, it is not penalising those people who have really high amounts of “good” HDL that make up their total cholesterol, which the first ratio does.

Research has suggested this ratio may be a stronger predictor of atherosclerosis in women than men, however more research is needed.

Another study followed more than 10,000 adults with type 2 diabetes from the United States and Canada for about five years. The researchers found that for each unit increase in the ratio, there was around a 12% increased risk of having a heart attack, stroke or death.

They identified a risk threshold of 6.28 or above, after adjusting for other risk factors. Anyone with a ratio greater than this is at very high risk and would require management to lower their risk of heart disease.

3. LDL-to-HDL cholesterol ratio

LDL/HDL is calculated by dividing your LDL cholesterol number by the HDL number. This gives a ratio of “bad” to “good” cholesterol.

A lower ratio (ideal is less than 2.0) is associated with a lower risk of heart disease.

While there is lesser focus on LDL/HDL, these ratios have been shown to be predictors of occurrence and severity of heart attacks in patients presenting with chest pain.

Read more: Health Check: five food tips that could save your life after a heart attack

If you’re worried about your cholesterol levels or cardiovascular disease risk factors and are aged 45 and over (or over 30 for First Nations people), consider seeing your GP for a Medicare-rebated Heart Health Check.