Carotid intima-media thickness measurement in cardiovascular screening programmes

Support for the notion that a carotid intima-media thickness (CIMT) measurement is useful in individual cardiovascular risk prediction in addition to a risk function may come from studies showing that for an individual a high or low CIMT measurement leads to a correct shift from one to another risk category and this shift is followed by different treatment consequences. We set out to systematically review the published evidence by performing a PubMed search (2 March 2009). Out of 50 publications on CIMT and future events, 31 reported on the relation in the correct domain, i.e. those free from symptomatic vascular disease or diabetes mellitus in which assessment of risk using a risk function (e.g. Framingham or SCORE) to base initiation of drug treatment upon is recommended. Most studies reported relative risks (or equivalents) for the entire population only, and no information on relative risks within certain risk categories that may be of use to reclassify individuals based on combination of absolute and relative risks. No data on potential shifts of participants was presented. Eight studies specifically focused on the added value of CIMT in risk prediction. In seven studies the area under the curve (AUC) of a receiver operating characteristic was used to assess improvements in risk prediction. These analyses showed that addition of a CIMT measurement to established risk factors led to small and sometimes significant improvements in the AUC. However, change in AUC should not be the only parameter to rely on to judge the appropriateness of CIMT in risk stratification. In one study (n = 242), evidence was presented in participants with an intermediate Framingham risk score, a CIMT measurement above the 60th (men) and 80th (women) percentile of age-specific normal CIMT values, shifted participants above the threshold for initiation of drug therapy. Yet, the study was based on 24 events, and no information was presented on the proportion of participants correctly shifted. At present it seems that the published evidence to quantitatively support the use of a CIMT measurement to help in risk stratification on top of a risk function is limited.