Cluster 274: hematocrit hct hemoglobin anemia donor dl reached days males transfusion Cluster 948: greater hemoglobin dl equal gm screening values visit transfusion level Cluster 1305: hb hemoglobin dl gm level transfusion correct transfusions equal anemia Cluster 1576: transfused gm hemoglobin dl rbcs achieve blood requirement prior level Cluster 2471: hemoglobin level dl reached transfusion eligibility gm days achieve registration