Medical Reasons for 'Weekend Effect' Elusive

"It's more likely a difference in how hospitals operate over the weekend as opposed to during the week, meaning that there may be a real opportunity for hospitals to change how they operate and save lives," Schneider said in prepared remarks.

A separate study published last month in the Archives of Surgeryreviewed 31,832 patient files and found worse outcomes for patients undergoing urgent surgery for left-sided diverticulitis who were admitted on the weekend versus weekdays.

"Patients undergoing urgent surgery for left-sided diverticulitis who are admitted on a weekend have a higher risk for undergoing a Hartmann procedure and worse short-term outcomes compared with patients who are admitted on a weekday," the study concluded. "Further research is warranted to investigate possible underlying mechanisms and to develop strategies for reducing this substantial weekend effect."

Previous studies have documented the weekend effect for heart attack, stroke, and aneurism, but none say precisely what is driving the phenomenon.

A March 2010 study from the federal Agency for Healthcare Research and Quality found that patients admitted to a hospital on a weekend are half as likely to get procedures they need on the same day they arrive than if they were admitted on a weekday. That study also found that 2.4% of patients admitted on the weekend died in the hospital, compared to 1.8% of patients admitted during the week.