Earlier this month, Dr. Thomas Robinson, a general surgeon at the Denver Veterans Affairs Medical Center, saw a patient in his mid 80s. The man had gallstones that caused infections, with abdominal pain severe enough to send him to an emergency room every couple of months.

The surgical solution to this problem is usually clear: Remove the gallbladder with a procedure called a cholecystectomy. “In a 60-year-old, chances are it’s an outpatient operation,” Dr. Robinson said. In this case, though, he hesitated. Like a growing number of surgeons, he wanted to know, before presenting the options, whether his patient was frail.

In geriatrics, frail is not merely an adjective. A syndrome marked by slowness, weakness, fatigue and often weight loss, frailty tells doctors a lot about their patients’ likely futures. It can, for example, predict how well older patients rebound from physical stresses — like surgery.

“Some 86-year-olds live independently and are really healthy, and we take out their gallbladders all the time,” Dr. Robinson told me. But this patient, a nursing home resident who also had heart disease and pulmonary disease, scored moderately to highly frail on a commonly used index.