Thousands of patients might be getting a raw deal over the way the NHS treats serious conditions because of gender stereotyping by doctors, a study warned last night.

Men admitted to intensive care units with heart attacks were significantly younger, less ill and had a lower hospital death rate than women, according to researchers who studied the histories of 45,687 patients in 91 units over three years.

The results suggested that hospitals' criteria for admission of patients to intensive care with blockage of the coronary artery were more stringent for women.

Other inequalities in favour of men were identified in treating primary brain injuries and neurological bleeding, while women appeared to get a better deal over admission for pneumonia and heart failure involving the ventricles, the lower chambers of the heart.

The study, by researchers at the London School of Hygiene and Tropical Medicine and the Intensive Care National Audit and Research Centre, London, involved hospitals in England, Wales and Northern Ireland. It found no suggestion of gender differences in other conditions. But the study's authors, writing in the Journal of Epidemiology and Community Health, suggested that "gender norms" might explain some findings.

If doctors expected certain conditions to be more common in men or women, then patients fitting the sterotype might be more readily treated and admitted to intensive care.

More research was needed. "In practical terms, gender bias can result in either the over-treatment in the favoured group or under-treament in the neglected group. Neither group is well served."