Bleeding Disorder Patients Warned Jan 6, 7:06 PM (ET) WASHINGTON (AP) - A small number of patients with a bleeding disorder have experienced a potentially life-threatening loss of red blood cells, the FDA and the manufacturer and distributor of a medicine that treats the disorder warned Friday. Patients with immune thrombocytopenic purpura, or ITP, should immediately alert their doctors if they experience back pain, shaking or chills, fever, discolored urine or decreased urine output, sudden weight gain, fluid retention, swelling or shortness of breath, Baxter Healthcare Corp. and Cangene Corp. said. The rare but sometime severe or fatal symptoms have been observed in ITP patients, the companies wrote in a letter to doctors last month. Reports of the most severe reactions occurred in patients treated with WinRho SDF, a medicine made and distributed by the two companies. Most reported adverse reactions within four hours of treatment, the companies said. The Food and Drug Administration released the letter Friday. Deerfield, Ill.-based Baxter distributes WinRho SDF, which is used to treat the disorder, marked by an abnormally low number of platelets in the bloodstream needed for blood to clot properly. Cangene, of Winnipeg, Canada, makes the immune therapy from donated human plasma. The companies revised the medicine's label to include the new warning. The revised label also warns that use of the liquid formulation of WinRho SDF can lead to falsely high blood glucose levels in certain types of blood glucose testing systems. WinRho SDF also is used also used to protect against the development of antibodies in patients with Rh-negative blood who are given Rh-positive blood, and in pregnancy to prevent an Rh-negative mother's immune system from destroying an Rh-positive baby's red blood cells, the companies said.