Reference intervals for carotid artery intima-media thickness measurements in the multi-ethnic Asian population: relationship with cardiometabolic risk factors

Abstract

Abstract Background Carotid artery intima-media thickness (cIMT) is an intermediate surrogate marker for cardiovascular disease (CVD). It has been reported that although the distribution of cIMT values is very heterogeneous and values vary widely between different ethnicity, geographic location, and ultrasound protocol, the prediction of vascular events with study-specific cIMT values is consistent across all ethnicities and regions (1). Hence, Consensus Statement from the American Society of Echocardiography suggests that cIMT greater than or equal to 75th percentile for the patient’s age, sex, and ethnicity is indicative of increased CVD risk (2). Aims We aimed to establish age, sex, and ethnic-specific reference intervals in the multi-ethnic Asian population comprising Chinese, Malays, and Indians. Methods We analysed data from 8762 healthy individuals who had a 3D carotid ultrasonography done as part of the Health for Life in Singapore study. Carotid ultrasonography measurements were taken from the distal common carotid artery (CCA) at both the lateral and posterior angles bilaterally during the end-diastolic phase. The mean of all 4 measurements were taken as average cIMT (avgcIMT). For this analysis, we excluded individuals on treatment for diabetes, hypertension, hyperlipidemia, and ischemic heart disease to derive a healthy population subset comprising of 6522 individuals (Chinese: 69%, Malays: 14%, Indians: 17%). We then assessed the 75th percentile as a marker of cardiovascular risk in all individuals, by testing associations with Framingham risk scores (locally adapted) and with cardiometabolic risk factors (3). Results Ethnic- and sex-specific 75th percentiles (95% CI) of CIMT for our Asian populations are summarised in Table 1. Compared to reference intervals reported in European and African American populations, the 75th centiles are lower in all Asian ethnic subgroups (p<0.05). Framingham risk score, BMI, LDL-C, HbA1c and systolic blood pressure were higher in Asians with cIMT more than 75th percentile (p<0.001), compared to Asians with normal cIMT. Conclusions We estimated race- and sex-specific 75th percentiles of avgcIMT across age in the multi-ethnic Asian population. The thresholds for Asian populations are substantially lower than reported in European and African populations. The 75th centiles identify people with raised cardiovascular risk factors, supporting the validity of cIMT as marker of vascular risk in the population. The 75th centiles will be useful in interpretation of cIMT measures obtained both in research and clinical settings in different ethnic populations in Asia. Longitudinal evaluation is needed to determine the prediction of our Asian specific thresholds for predicting hard cardiovascular outcomes.