Haemoglobin concentration and the risk of death in older adults: differences by race/ethnicity in the NHANES III follow-up

Abstract

Mildly low haemoglobin concentration is associated with increased mortality in older adults. However, this relationship has not been well characterized in racial/ethnic minorities. Therefore, this study determined the haemoglobin threshold below which risk of death is significantly increased in older non-Hispanic whites, non-Hispanic blacks, and Mexican Americans. Data on 4089 participants of the 1988-94 US National Health and Nutrition Examination Survey who were > or =65 years of age were analyzed with mortality follow-up through December 31, 2000. Mean haemoglobin in non-Hispanic whites (n = 2686) and Mexican Americans (n = 663) was 140 g/l, while in non-Hispanic blacks (n = 740) the mean was 10 g/l lower. A total of 1944 (47.5%) participants died. Among non-Hispanic whites and Mexican Americans, age- and sex-adjusted models showed that the haemoglobin thresholds below which mortality risk was significantly increased were 4 and 2 g/l respectively, above the World Health Organization (WHO) cut-off points for anaemia. In contrast, the threshold for non-Hispanic blacks was 7 g/l below the WHO criteria. Similar threshold effects were observed when analyzing haemoglobin in categories and adjusting for multiple confounders. In conclusion, the haemoglobin threshold below which mortality rises significantly is a full g/dl lower in non-Hispanic blacks than in non-Hispanic whites and Mexican Americans.

Figure 1. Survival plots of older adults by hemoglobin level and race/ethnicity, NHANES III (1988-1994)

Figure 2. Age and sex adjusted association of hemoglobin concentration with mortality in older adults, by race/ethnicity*

*Note: The x-axis is centered on the WHO cut points for anaemia and therefore the 0 value corresponds to hemoglobin of 120 g/L in women and 130 g/L in men. The dotted vertical line indicates where the risk of death is significantly increased (lower bound of the 95% CI is above 0.0), while dashed lines are the 95% CI.