Performance of cardiovascular risk prediction equations in Indigenous Australians

OBJECTIVE

To assess the performance of cardiovascular disease (CVD) risk equations in Indigenous Australians.

METHODS

We conducted an individual participant meta-analysis using longitudinal data of 3618 Indigenous Australians (55% women) aged 30-74 years without CVD from population-based cohorts of the Cardiovascular Risk in IndigenouS People(CRISP) consortium. Predicted risk was calculated using: 1991 and 2008 Framingham Heart Study (FHS), the Pooled Cohorts (PC), GloboRisk and the Central Australian Rural Practitioners Association (CARPA) modification of the FHS equation. Calibration, discrimination and diagnostic accuracy were evaluated. Risks were calculated with and without the use of clinical criteria to identify high-risk individuals.

RESULTS

When applied without clinical criteria, all equations, except the CARPA-adjusted FHS, underestimated CVD risk (range of percentage difference between observed and predicted CVD risks: -55% to -14%), with underestimation greater in women (-63% to -13%) than men (-47% to -18%) and in younger age groups. Discrimination ranged from 0.66 to 0.72. The CARPA-adjusted FHS equation showed good calibration but overestimated risk in younger people, those without diabetes and those not at high clinical risk. When clinical criteria were used with risk equations, the CARPA-adjusted FHS algorithm scored 64% of those who had CVD events as high risk; corresponding figures for the 1991-FHS were 58% and were 87% for the PC equation for non-Hispanic whites. However, specificity fell.

CONCLUSION

The CARPA-adjusted FHS CVD risk equation and clinical criteria performed the best, achieving higher combined sensitivity and specificity than other equations. However, future research should investigate whether modifications to this algorithm combination might lead to improved risk prediction.

Associations of mortality and cardiovascular disease risks with diabetes and albuminuria in urban Indigenous Australians: the DRUID follow-up study

AIM

To assess the relationships of diabetes and albuminuria with all-cause mortality and cardiovascular disease outcomes in a population without prior cardiovascular disease using data from the Darwin Region Urban Indigenous Diabetes (DRUID) study.

METHODS

We conducted a prospective cohort study of 706 participants (aged 15-81 years, 68% women) without prior cardiovascular disease who underwent a 75-g oral glucose tolerance test. Deaths and fatal or non-fatal cardiovascular disease were determined over 7 years, and hazard ratios with 95% CIs and population attributable risks were estimated for baseline glycaemia and albuminuria.

RESULTS

Compared with normoglycaemia and after adjustment for age, sex, hypertension, dyslipidaemia and smoking, known diabetes was associated with an adjusted hazard ratio of 4.8 (95% CI 1.5-14.7) for all-cause mortality and 5.6 (95% CI 2.1-15.2) for cardiovascular disease. Compared with normoalbuminuria, the respective adjusted risks for macroalbuminuria were 10.9 (95% CI 3.7-32.1) and 3.9 (95% CI 1.4-10.8). The Adjusted all-cause mortality and cardiovascular disease estimated population attributable risks for diabetes were 27% and 32%, and for albuminuria they were 32% and 21%, respectively.

CONCLUSIONS

In our study population, the burden of mortality and cardiovascular disease was largely driven by diabetes and albuminuria. This finding on the influence of diabetes and albuminuria is consistent with reports in other high-risk Indigenous populations and should be better reflected in risk scores and intervention programmes.

Association of retinal vessel calibre with diabetic retinopathy in an urban Australian indigenous population

PURPOSE

To assess the relationship of retinal vessel diameter and diabetic retinopathy (DR) in a subgroup of participants recruited through the Darwin Region Urban Indigenous Diabetes study.

METHODS

Participants were examined as part of the Darwin Region Urban Indigenous Diabetes study. All participants with gradable fundus photographs were included in the current analysis. Assessment of retinal vascular diameter, including arteriolar diameter (central retinal arteriolar equivalent) and venular diameter (central retinal venular equivalent), was undertaken using a semi-automated retinal vascular imaging program. DR was graded according to the modified Early Treatment DR Study scale.

RESULTS

A total of 110 participants, 25 men and 85 women, with a mean age of 50.8 years were included in the analysis. The odds ratio for having DR for each standard deviation increase in central retinal venular equivalent was as high as 1.62 (95% confidence intervals 0.94, 2.80); however, this did not reach statistical significance (P = 0.08). Moreover, individuals with severe non-proliferative DR and proliferative DR were found to have narrower arteriolar diameters compared with those with no DR, but this was not statistically significant (-8.1 microm, 95% confidence intervals, -39.3 microm, 23.1 microm; P = 0.612).

CONCLUSION

Our data indicate a trend for narrower arteriole diameter and wider venular diameter with DR in this high-risk ethnic group, which concurs with overall trends seen in non-indigenous populations.

Complications of diabetes in urban Indigenous Australians: the DRUID study

AIMS

To accurately assess the management and complications of type 2 diabetes in urban Indigenous Australians and compare the risk of complications with a general Australian population (AusDiab Study).

METHODS

The Darwin Region Urban Indigenous Diabetes (DRUID) Study included 1004 volunteers aged >/=15 years; diabetes status was classifiable for 866. The assessment of diabetic complications and metabolic control was performed in participants with known diabetes (KDM) and diabetes newly diagnosed by the study (NDM) using an interviewer-administered questionnaire and clinical examination.

RESULTS

Among 172 DRUID participants eligible for complications assessment, 135 were assessed, including 99 KDM (mean age 53 years) and 36 NDM (mean age 47 years). Percentages of KDM participants meeting therapeutic targets were: HbA1c<7%, 29%; blood pressure<130/80mmHg, 45%; total cholesterol<5.5mmol/L, 65%. Among KDM, 39% had albuminuria, 21% retinopathy, 12% peripheral vascular disease (PVD), 9% neuropathy. Factors independently associated with diabetic complications were: albuminuria-HbA1c, systolic blood pressure; retinopathy-diabetes duration; PVD-age. Compared to AusDiab participants after adjusting for other risk factors, DRUID participants had 2-3-fold increased risk of albuminuria and PVD and a non-significant increased risk of neuropathy, but no increased risk of retinopathy.

CONCLUSIONS

Urban Indigenous Australians with diabetes are relatively young and have poor glycaemic control. Compared to the general Australian population with type 2 diabetes, they have greater adjusted risk of albuminuria and PVD but not retinopathy. Urgent action is required to prevent diabetes at a population level and improve diabetes management in this high-risk population.