Comparative assessment of absolute cardiovascular disease risk characterization from non-laboratory-based risk assessment in South African populations

Abstract

Background: All rigorous primary cardiovascular disease (CVD) prevention guidelines recommend absolute CVD risk scores to identify high- and low-risk patients, but laboratory testing can be impractical in low- and middle-income countries. The purpose of this study was to compare the ranking performance of a simple, non-laboratory-based risk score to laboratory-based scores in various South African populations.

Methods: We calculated and compared 10-year CVD (or coronary heart disease (CHD)) risk for 14,772 adults from thirteen cross-sectional South African populations (data collected from 1987 to 2009). Risk characterization performance for the non-laboratory-based score was assessed by comparing rankings of risk with six laboratory-based scores (three versions of Framingham risk, SCORE for high- and low-risk countries, and CUORE) using Spearman rank correlation and percent of population equivalently characterized as 'high' or 'low' risk. Total 10-year non-laboratory-based risk of CVD death was also calculated for a representative cross-section from the 1998 South African Demographic Health Survey (DHS, n = 9,379) to estimate the national burden of CVD mortality risk.

Results: Spearman correlation coefficients for the non-laboratory-based score with the laboratory-based scores ranged from 0.88 to 0.986. Using conventional thresholds for CVD risk (10% to 20% 10-year CVD risk), 90% to 92% of men and 94% to 97% of women were equivalently characterized as 'high' or 'low' risk using the non-laboratory-based and Framingham (2008) CVD risk score. These results were robust across the six risk scores evaluated and the thirteen cross-sectional datasets, with few exceptions (lower agreement between the non-laboratory-based and Framingham (1991) CHD risk scores). Approximately 18% of adults in the DHS population were characterized as 'high CVD risk' (10-year CVD death risk >20%) using the non-laboratory-based score.

Conclusions: We found a high level of correlation between a simple, non-laboratory-based CVD risk score and commonly-used laboratory-based risk scores. The burden of CVD mortality risk was high for men and women in South Africa. The policy and clinical implications are that fast, low-cost screening tools can lead to similar risk assessment results compared to time- and resource-intensive approaches. Until setting-specific cohort studies can derive and validate country-specific risk scores, non-laboratory-based CVD risk assessment could be an effective and efficient primary CVD screening approach in South Africa.

Figure 1

Rank variables for the non-laboratory-based risk score are plotted against rank variables for the Framingham (2008) CVD score for adults 25 to 74 years old with complete data in the aggregate study population. Larger ranks indicate greater CVD risk. Based on a risk threshold that corresponds to 10-year Framingham (2008) CVD risk >20%, 92.3% of men (panel a, shaded regions) and 94.0% of women (panel b, shaded regions) would be similarly characterized as high or low risk by the non-laboratory-based and Framingham (2008) CVD risk scores.

Figure 2

Histograms of 10-year non-laboratory-based CVD death risk are plotted for the aggregate study population and the representative DHS (South Africa, 1998) populations by sex for adults ages 25–74 years (age-adjusted for WHO Segi ‘world’ reference population). The study population has a slightly higher risk profile compared to the DHS population in the middle ranges (10% to 30% to 40%), although the overall distributions of risk are mostly similar between these populations for both men and women. Histogram of non-laboratory-based risk (10-year risk of CVD death) for adults in the study sample and DHS 98 population. CVD, cardiovascular disease; DHS, Health and Demographic Survey; WHO, World Health Organization.

Figure 3

Percentages of adults ages 25–74 years from the aggregate study population and the representative DHS (South Africa, 1998) populations that are greater than specified non-laboratory-based 10-year CVD death risk thresholds are plotted by sex (age-adjusted for WHO Segi ‘world’ reference population). For men, the study population has a slightly higher risk profile compared to the DHS population in the lower-to-middle risk thresholds (>20% to >30%), although the overall distributions of risk are mostly similar between these populations for both men and women. Percent of adults in the study sample, and DHS 98 population, above selected non-laboratory-based thresholds (10-year CVD death risk). CVD, cardiovascular disease; DHS, Health and Demographic Survey; WHO, World Health Organization.