Researchers said that while adrenal insufficiency was common in ICU patients, little was known about the effect of adrenal function change during prolonged critical illness.
They observed 53 acutely ill patients over periods of up to 41 days, with cortisol levels tested on average every eight days.
The majority of patients whose condition did not improve had lower serum cortisol levels at follow-up.
Repeat testing should be done even when adrenal function on admission is normal, the researchers said.
Critical Care (2008) 12: R65