A higher urinary albumin-to-creatinine ratio was associated with an increased risk of incident coronary heart disease in black adults in the large, population-based REGARDS study.
No such association was seen in white adults in the prospective cohort study, suggesting that black individuals are more susceptible to vascular injury, according to Dr. Orlando M. Gutierrez of the University of Alabama at Birmingham and his colleagues, who reported the findings on behalf of the Reasons for Geographic and Racial Differences in Stroke (REGARDS) investigators.
Over a mean follow-up period of 4.5 years, 616 incident coronary heart disease events – 421 nonfatal myocardial infarctions and 195 CHD deaths – occurred in 23,273 individuals who were free of CHD at baseline. The incidence rates of CHD per 1,000 person-years of follow-up increased with increasing albumin-to-creatinine ratio (ACR) in these patients, and the increases were significantly greater for black adults, compared with white adults, the investigators reported. The study was published in the Aug. 21 issue of JAMA.
Age- and sex-adjusted incidence rates were nearly 1.5-fold greater in black adults than in white adults in the two highest categories of ACR: For black vs. white participants with ACR of 30-300 mg/g, the incidence rates per 1,000 person years were 11.2 and 8.0, respectively, and for those with ACR greater than 300 mg/g, the rates were 20.6 and 13.6, respectively, both significant differences.
After adjustment for traditional cardiovascular risk factors and medications, higher baseline urinary ACR (greater than 300 mg/g vs. less than 10 mg/g) was associated with greater risk of incident CHD among blacks, but not whites (hazard ratios of 3.21 and 1.49, respectively), they said.
A similar association was not seen for recurrent CHD. Over 4.4 years of follow-up, 468 recurrent CHD events – 279 nonfatal MIs and 189 CHD deaths – occurred in 4,934 individuals who had CHD at baseline. No differences were seen between black and white adults in this group with respect to baseline urinary ACR and first recurrent CHD event (JAMA 2013; 310:706-13).
The REGARDS study, a population-based investigation of stroke incidence in black and white adults in the United States, comprised individuals aged 45 years and older at baseline between 2003 and 2007, and oversampled those who self-reported as black and those living in the U.S. stroke belt.
Black individuals are known to have higher levels of urinary albumin excretion than those of white individuals – a finding that may contribute to racial disparities in cardiovascular outcomes. Previous REGARDS study findings showed that an association between urinary ACR and incident stroke differed by race, and that higher urinary ACR was independently associated with a greater risk of incident stroke in blacks, but not whites, the investigators said.
However, little is known about racial differences with respect to the association of urinary ACR and cardiovascular outcomes apart from stroke, they noted.
"These findings confirm the results of prior studies showing that urinary ACR is an important biomarker for CHD risk in the general population, even among individuals with ACR values that are less than the current threshold for defining microalbuminuria (30 mg/g). Additionally, to our knowledge, this is the first study to demonstrate that the higher risk of incident CHD associated with excess ACR differs by race," they said.
The findings contribute to increasing evidence suggesting that blacks are more susceptible than are whites to vascular injury, and suggest that this greater susceptibility may account for much of the excess risk of cardiovascular disease events, including stroke and CHD, in black individuals, they added.
This study is limited by a number of factors, including the use of a single measure of ACR, which may have led to exposure misclassification for some patients, and also by reduced power to detect significant associations due to relatively few events occurring in some ACR categories. Also, only black and white adults were included in REGARDS, which may limit the applicability of the results to other races and ethnicities, the investigators noted.
Nonetheless, the findings indicate that higher urinary ACR is a strong risk factor for incident CHD events (but not recurrent CHD events) in black vs. white individuals, they said, concluding that future studies should examine whether the addition of ACR can improve the diagnosis and management of CHD in black individuals.
This study was supported by a cooperative agreement from the National Institute of Neurological Disorders and Stroke and from the National Heart, Lung, and Blood Institute. Dr. Gutierrez was supported by grants from the National Institute of Diabetes and Digestive and Kidney Diseases and from NINDS. Amgen provided funding in the form of an investigator-initiated grant-in-aid. Several study authors disclosed ties with Amgen, REATA Pharmaceuticals, Arbor Research, Sanofi-Genzyme, and/or diaDexus.