Triglyceride to HDL ratio

The UK thresholds

Robert Lustig, the paediatric endocrinologist whose work underpins much of the modern metabolic health movement, puts the problem line at 2.5 and the target nearer 1.5. Those are mg/dL figures. On a UK panel reporting mmol/L, the same lines land at 1.09 and 0.65.

He also states the threshold is lower for people of Black African or Caribbean background, nearer 1.5 as the problem line rather than 2.5. In UK terms that is a problem line of 0.65 rather than 1.09. The calculator has a lower-target setting for this. One honest caveat, though: the wider evidence is mixed here. Several studies find the ratio a less reliable marker of insulin resistance in people of Black African descent — particularly women — because triglycerides can stay low even when insulin resistance is present. Treat a result in this group as a weaker signal rather than a firm line, and lean on fasting glucose, HbA1c and waist instead.

Two further Lustig targets, converted: triglycerides below 100 mg/dL becomes below 1.1 mmol/L, and HDL above 60 mg/dL becomes above 1.55 mmol/L.

The unit trap that makes UK results look better than they are

Nearly every article about this ratio quotes the American numbers without saying so. Triglycerides in mg/dL are the mmol/L figure multiplied by roughly 88.6; HDL in mg/dL is the mmol/L figure multiplied by roughly 38.7. Because the two convert at different rates, the ratio itself shifts by a factor of about 2.29 between the systems.

Work an example. Triglycerides of 1.8 mmol/L with HDL of 1.1 mmol/L gives a ratio of 1.64. Read against "below 2.5 is fine", that looks comfortable. Convert to the mg/dL scale those thresholds came from and the same blood gives 3.75, well past the problem line. Same person, same panel, opposite conclusion.

If you are working it out by hand from a UK panel, either compare against the mmol/L column in the table above, or multiply your ratio by 2.29 before using any threshold you read elsewhere.

What the ratio actually measures

High triglycerides with low HDL is the fingerprint of insulin resistance on a lipid panel. When the liver is handling more sugar and fat than it can process, it exports the surplus as triglycerides, and the same process depletes HDL. Two numbers moving in opposite directions for one reason, which is why the ratio carries more information than either alone.

Lustig's argument for it goes a step further: triglycerides that have unloaded their fat at adipose tissue become small dense LDL, the most atherogenic particle. That makes this ratio a proxy for particle quality, which a standard total cholesterol figure cannot see at all. It is the reason he treats it as the most useful line on the panel for both cardiovascular risk and insulin resistance.

What the ratio is not

It is not an NHS or NICE clinical target. UK cholesterol treatment decisions run on non-HDL cholesterol and the QRISK score. No GP will start or stop a statin because of this ratio.

Its value is different: it turns a panel you already have into an early read on insulin resistance, often years before glucose rises. Treat it as a signal to investigate, not a diagnosis to act on alone.

Where it fits with your other numbers

Triglycerides and HDL are two of the five components of metabolic syndrome. Blood pressure is another, and you can check yours with our blood pressure checker. The five travel together because they share one cause, so a ratio drifting upward rarely drifts alone.

If your ratio sits above the target, the numbers worth having next are fasting glucose or HbA1c, your waist measurement, and your blood pressure. Lustig also recommends a fasting insulin test, targeting below 6 mIU/L, though UK GPs rarely order it.

What moves the ratio

Triglycerides respond faster to diet than almost any other blood marker. Cutting refined carbohydrate, sugary drinks, and alcohol can move them within weeks. HDL shifts more slowly and responds mainly to exercise, weight loss, and stopping smoking.

Because triglycerides move quickly, the ratio moves quickly too, which makes it a satisfying number to track. Two panels six months apart will usually show whether a change in habits landed.

One practical note: triglycerides are sensitive to whether you fasted before the test. A non-fasting sample reads higher, so compare like with like when you look back at old results.

Track the ratio, not the single panel

A ratio calculated once tells you where you stand today. The same calculation across three or four panels tells you which way your metabolism is heading, and gives your GP something better than a single line on a printout.

BioMetRx stores every lab result you enter, calculates this ratio automatically, and plots it alongside your blood pressure, waist, weight, and glucose. See how it works.

Frequently asked questions