OBJECTIVE to determine whether the laboratory hematic curve must be the single predictor of postoperative blood transfusion in total hip arthroplasty. METHODS the laboratory blood samples of 78 consecutive patients undergoing total hip arthroplasty was analyzed during five distinct moments: one preoperative and four postoperative. There was a count of hemoglobin, hematocrit and platelets of the patients samples. Other catalogued variables ascertain possible risk factors related to transfusional practice. They characterized the anthropometric, behavioral and co morbidities data in this population. The study subjects were divided and categorized into two groups: those who received blood transfusion during or after surgery (Group 1, G1), and those who did not accomplish blood transfusion (Group 2, G2). Transfusion rules were lead by guidelines of American Academy of Anesthesiology and the British Society of Hematology. RESULTS a total of 27 (34.6%) patients received blood transfusions. The curves of hemoglobin, hematocrit and platelet transfusions between G1 and G2 were similar (p > 0.05). None of the analyzed risk factors modified the rate of transfusion rate in their analysis with p value > 0.05, except the race. The sum of clinical co morbidities associated with patients in G1 was a median of 3 (95% CI 2.29-3.40), while in G2 the median was 2 (95% CI 1.90-2.61) with p = 0.09. CONCLUSION the curve in red blood cells has limited reliability when used as sole parameter. The existence of tolerant patients hematimetric curve variations assumes that their assessments of clinical, functional evaluation and co-morbidities are parameters that should influence the decision to transfusion red blood cells.