TC/HDL ratio

Your total cholesterol is a sum: the cholesterol in LDL particles, which can lodge in the vessel wall, in the particles that carry triglycerides, and in HDL particles, which bring cholesterol back out of the vessel wall. That makes the total a coarse number: a high total can come from a lot of depositing cholesterol, but also from a lot of protective HDL, and those are opposite situations. The TC/HDL ratio divides the total by HDL and pulls that difference out: with a lot of HDL the denominator is large and the ratio low, with little HDL the other way round. That is why the ratio says more than the total alone, and why it is the one lipid ratio a Dutch lab prints, with a target below 5. The ratio was for years the number on which vascular risk was estimated, before the risk estimate moved to LDL itself and to non-HDL. The limitation is the same as with every division: a low total with a low HDL gives the same number as a higher total with a high HDL, and those are two different situations. Your report prints the ratio at some of the labs; otherwise you calculate it with the calculator on this page, from total cholesterol and HDL in mmol/L. The result has no unit. Below 5 is the target, and anyone who eats well, exercises and does not smoke usually sits around 3 to 4; the lower, the better.

The ratio is the quickest way to read a total cholesterol. Anyone who sees a total of 6 and is alarmed sees from the ratio whether there is an HDL of 2 in it, and then the ratio is 3 and the profile healthy, or an HDL of 1, and then the ratio is 6 and there is too much depositing cholesterol in it. That difference decides whether you need to do something, and the total alone does not show it. The second reason is that the ratio shows the gain of lifestyle on two sides. Less saturated fat and more fibre lower the total; exercise, losing weight and stopping smoking lift HDL; and the ratio falls on both fronts. Anyone who tackles their cholesterol with diet and exercise often sees the ratio move earlier than the total alone. The honest limitation is that the Dutch risk estimate now works with other numbers: LDL itself and non-HDL, which counts all cholesterol in depositing particles, and ApoB, which counts those particles directly. A high HDL also protects less than was long thought, and a ratio that is low through a very high HDL can hide an LDL that is too high in itself. The ratio is a summary; the decision on a statin falls on LDL and non-HDL.

A low ratio is favourable, and the only question is by which route. Plant-based, fibre-rich eating, a healthy weight and plenty of exercise lower the total and lift HDL, and that is the healthy route. Lipid-lowering medicines lower the total specifically and bring the ratio down without HDL moving. A high HDL makes the denominator larger without anything changing about the depositing cholesterol; so always check whether LDL itself sits below the limit that fits your risk. A high ratio means proportionally a lot of depositing and little protective cholesterol is circulating. From common to rare: a lot of saturated fat in the diet, from fatty meat, full-fat dairy, butter, coconut fat and biscuits, which lifts LDL and with it the total; excess weight and little exercise, which lower HDL and make the denominator smaller, as does smoking; an underactive thyroid, which slows the breakdown of LDL; and rarely familial hypercholesterolaemia, with an LDL above 5 mmol/L from childhood. Above 5 the ratio is outside the target, and then the question about your total vascular risk belongs with it. Set the ratio beside total cholesterol and HDL themselves, because the same ratio belongs to several combinations, beside LDL, non-HDL and ApoB, which the risk estimate works on, and beside the triglycerides, which count in the total.