First-week Postoperative Morning Serum Cortisol Nadir as a Potential Rule-Out Marker for Secondary Adrenal Insufficiency After Pituitary Surgery: A Retrospective Cohort Study

The pituitary gland, a small structure tucked deep at the base of the brain, acts as the body's master control center for many vital hormones. Among its most critical jobs is signaling the adrenal glands, which sit atop the kidneys, to produce cortisol. Cortisol is a hormone essential for managing stress, regulating blood sugar, and keeping the immune system in check. When the pituitary gland is damaged or removed, this signaling chain can break, leaving the body unable to produce enough cortisol on its own. This condition, known as secondary adrenal insufficiency, can be dangerous and even life-threatening if not recognized and treated quickly. Because of this risk, patients who undergo surgery to remove pituitary tumors are often given steroid medication to replace the missing hormone. However, giving these drugs to everyone, even those whose bodies can still make their own cortisol, exposes them to unnecessary side effects. The medical challenge has been finding a reliable way to tell, right after surgery, which patients truly need the medication and which ones can safely stop taking it.

Researchers at Curry Cabral Hospital and São José Hospital in Portugal set out to solve this problem by looking for a specific clue in the blood. They focused on the lowest level of cortisol measured in the morning during the first week after pituitary surgery. In their study, they reviewed the records of 116 adults who had undergone transsphenoidal surgery, a common procedure where surgeons remove pituitary tumors through the nose. The team excluded patients who already had known adrenal problems or a specific type of tumor called Cushing's disease, focusing instead on those whose adrenal systems were working normally before the operation. For every patient, the doctors recorded the lowest morning cortisol value found within the first seven days after the operation. They then followed these patients for up to a year to see who developed secondary adrenal insufficiency and who did not.

The results revealed a clear dividing line. Patients who eventually developed adrenal insufficiency had very low cortisol levels in the days following their surgery, with a median low point of just 1.30 micrograms per deciliter. In contrast, patients whose adrenal systems remained healthy had much higher levels, with a median low point of 11.50 micrograms per deciliter. The researchers analyzed these numbers to find a threshold that could act as a safety net. They discovered that if a patient's lowest morning cortisol reading during that first week was 6.7 micrograms per deciliter or higher, it was a strong indicator that their adrenal function was intact. This single measurement proved to be an excellent rule-out tool. At the three-month mark, this threshold yielded an AUC of 0.967, and at the one-year mark, it remained highly accurate, yielding an AUC of 0.913.

Perhaps most importantly for patient care, this threshold was exceptionally good at ruling out the disease when it was absent. If a patient's cortisol level was at or above 6.7 micrograms per deciliter, the chance that they would be diagnosed with adrenal insufficiency later was extremely small. The study found that using this cutoff would have prevented unnecessary steroid treatment for the vast majority of patients, with only a tiny fraction of healthy individuals being mistakenly sent home without medication. The researchers noted that while a few patients who met this safe threshold did eventually show signs of adrenal issues, these cases were rare and often involved complex factors like other medications or delayed recovery. The study concludes that measuring this specific morning cortisol level offers a practical, inexpensive way to personalize post-surgery care, allowing doctors to confidently stop steroid treatment for patients who do not need it, while ensuring those who do receive the life-saving support they require.