Low-dose aspirin increases the risk of anaemia in healthy older adults, independently of major bleeding, according to an analysis of the primary prevention ASPREE trial.

During ASPREE, 19,114 people aged 70 years and older (65 years and older for Black and Hispanic participants) from Australia and the US received daily either 100mg of enteric- coated aspirin or a placebo. 

Researchers defined anaemia as haemoglobin levels of less than 130g/L for men and less than 120g/L for women. Follow-up lasted a median of 4.7 years. 

Allowing for confounders, anaemia was 19 per cent more common in people who received aspirin compared with placebo: 51.2 and 42.9 per 1,000 person-years respectively. An estimated 23.5 and 20.3 per cent of those taking aspirin and placebo respectively developed anaemia within five years. 

Haemoglobin concentrations, which were measured annually, declined by, on average, 3.6g/L per five years in the placebo group. The rate of decline was found to be steeper (by 0.6g/L per five years) in those who received aspirin.

Researchers also measured ferritin (low levels indicate iron deficiency) in 7,139 participants at baseline and after three years. Ferritin levels less than 45mg/L at after three years were more common in those who received aspirin compared with placebo (13.0 and 9.8 per cent respectively). 

Serum ferritin levels declined by averages of 16 and 3 per cent with aspirin and placebo respectively. After allowing for baseline levels, ferritin concentrations decreased by, on average, 11.5 per cent more with aspirin than placebo after three years.

The researchers suggest that occult blood loss and minor bleeds, especially over several years, could cause anaemia. They advocate monitoring haemoglobin in older persons receiving aspirin.

Ann Intern Med doi:10. 7326/M23-0675