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132 Atherogenic coefficient (AC)

Atherogenic coefficient (TC − HDL-C)/HDL-C: calculation, conventional norm below 3, relation to non-HDL cholesterol and the Castelli index.

The atherogenic coefficient (AC), known in Eastern European practice as the Klimov coefficient, is the ratio of cholesterol in atherogenic lipoproteins to cholesterol in HDL. It shows how much cholesterol travels in particles that deposit it in artery walls (LDL, VLDL, IDL) for each unit carried by HDL, which removes it. The higher the coefficient, the more the balance is shifted towards atherosclerosis.

Lipid indicesNon-HDL cholesterolCardiovascular risk

Formula(TC − HDL-C) / HDL-C

Conventional norm< 3.0

Raised3–4

High> 4

How it is calculated

AC = (total cholesterol − HDL-C) / HDL-C = non-HDL-C / HDL-C

Example: total cholesterol 5.2 mmol/L and HDL-C 1.3 mmol/L give AC = 3.9 / 1.3 = 3.0. The numerator, non-HDL cholesterol, includes the cholesterol of all apoB-containing particles. The coefficient is equal to the Castelli index (TC/HDL-C) minus one, so AC = 3 corresponds to TC/HDL-C = 4. Because it is a ratio, the result is the same in mmol/L and mg/dL.

Figure 1. Conventional interpretation of the atherogenic coefficient. Cut-offs are traditional laboratory values, not guideline targets.

Clinical significance

AC rises when LDL or VLDL cholesterol is high, when HDL-C is low, or both. It is typically high in familial and polygenic hypercholesterolaemia, in insulin resistance and type 2 diabetes, hypothyroidism and chronic kidney disease. Ratios such as AC and TC/HDL-C predict coronary risk in population studies. However, the European and American guidelines set treatment goals for LDL-C, with non-HDL-C and apoB as secondary targets, not for ratios. A "normal" ratio with a high LDL-C, or with both values high, does not exclude risk.

Raises AC

Saturated and trans fats, excess weight, inactivity, smoking, diabetes, hypothyroidism, genetic hypercholesterolaemia.

Lowers AC

Mediterranean-type diet, regular exercise, weight loss, stopping smoking, statins and other lipid-lowering drugs when indicated.

What to do

Use the coefficient as a summary of your lipid profile, but discuss treatment based on LDL-C, non-HDL-C and your overall cardiovascular risk with a doctor.

References

Mach F, Baigent C, Catapano AL, et al. 2019 ESC/EAS Guidelines for the management of dyslipidaemias: lipid modification to reduce cardiovascular risk. Eur Heart J. 2020;41(1):111–188. doi:10.1093/eurheartj/ehz455
Grundy SM, Stone NJ, Bailey AL, et al. 2018 AHA/ACC/AACVPR/AAPA/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA guideline on the management of blood cholesterol. Circulation. 2019;139(25):e1082–e1143. doi:10.1161/CIR.0000000000000625
Dobiášová M, Frohlich J. The plasma parameter log (TG/HDL-C) as an atherogenic index: correlation with lipoprotein particle size and esterification rate in apoB-lipoprotein-depleted plasma (FER_HDL). Clin Biochem. 2001;34(7):583–588. doi:10.1016/S0009-9120(01)00263-6

This article is for general information and does not replace a consultation with a doctor. Laboratory results must be interpreted by a physician together with symptoms and other tests.

Published on 22 April 2024