More news today from the turbulent world of medical debt. Minnesota's attorney general is suing the biggest hospital system in the Twin Cities, alleging that Allina Hospitals & Clinics is violating a state law by charging patients excessive interest on unpaid bills.

"Allina has dug a deeper financial hole for patients facing tough economic times by charging usurious interest rates of up to 18 percent on medical bills," AG Lori Swanson said in a statement.

The...