Type of cholesterol and CHD risk effect
Q Some patients, particularly women, seem to have a high total cholesterol, but have a high HDL with or without a high LDL. If their total cholesterol to HDL ratio is normal, how should they be advised about their risk?
A Circulating cholesterol exists in different forms of lipoproteins. Low-density lipoproteins (LDL) are pro-atherogenic, whereas high-density lipoproteins (HDL) protect against atherosclerosis. In the last few years it has been suggested the ratio of total to HDL cholesterol may be more predictive of cardiovascular disease than LDL or HDL alone. Indeed, this concept has been borne out by large studies.
The Joint British Societies coronary risk prediction chart uses the ratio of total/HDL cholesterol in the calculation of 10-year CHD risk.
This scheme works well over a wide range of total and HDL cholesterol values.
But data at the extremes of HDL cholesterol concentration is limited; in particular, very little data is available for HDL above 1.8mmol/l.
The general consensus is that up to an HDL of 1.8mmol/l patients should have cardiovascular risk assessed according to the standard risk calculators, which emphasise the total/ HDL cholesterol ratio. If this ratio is normal it is advisable to recheck the full lipid profile at yearly intervals.
Above an HDL of 1.8mmol/l it may be more appropriate to base decisions on the absolute level of LDL; indeed, with high LDL too, it is appropriate to refer the patient to a lipid clinic, not least because a very high HDL may be associated with other abnormalities.
Albert Ferro is senior lecturer in clinical pharmacology,
King's College London