Tufts Medical Center has begun warning thousands of patients that Tufts doctors will no longer accept Blue Cross Blue Shield HMO coverage after Jan. 31, asserting in a letter that the state's largest health insurer refuses to pay Tufts doctors at a "reasonable rate." The medical center is asking its patients to contact Blue Cross directly to "express your frustration." The unusual move carries enormous risks for Tufts as well as for patients, who may be faced with the difficult choice of changing insurance coverage or changing hospitals in the next few weeks. The last time a hospital took the...