Factors Associated with Epoetin Response: METHODS
Retrospective chart reviews were conducted for all male patients who began epoetin therapy for anemia secondary to CKD or cancer between January 1, 2002, and December 31, 2003, at the Fargo VA Medical Center. Patients were excluded from the study if (1) they underwent a phlebotomy or multiple transfusions (i.e., on more than one occasion) during the study period; (2) if they had a history of hemochromatosis; or (3) if the date of the initiation of epoetin therapy could not be determined.
Subjects who received only one transfusion during the eight-week course of epoetin were included in the study. To account for the transfusion, we decreased the corresponding hemoglobin level by 1 g/dl per unit of red blood cells transfused.
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We collected the following demographic information: the patient’s age and weight, the indication for epoetin, the epoetin dose, and whether the patient had diabetes. We documented baseline ferritin levels, baseline transferrin saturation, and hemoglobin levels. Concomitant iron supplements, diuretics, angiotensin converting enzyme (ACE)-inhibitors, beta-adrenergic antagonists, aspirin, and chemotherapy were noted.
We examined the epoetin response rate. A response was defined as an increase in hemoglobin of 2 g/dl or greater after eight weeks of epoetin therapy. Patients were categorized into two groups. Responders had at least a 2-g/dl increase in hemoglobin after eight weeks of epoetin therapy; Nonresponders had less than a 2-g/dl increase in hemoglobin after eight weeks.
Two sample t-tests were used to measure differences in age, weight, hemoglobin and ferritin levels, and transferrin saturation between the two groups. Chi-square or Fisher’s exact tests were used to compare the remaining nominal variables for these groups.
We used stepwise logistic regression to identify any factors associated with a response to epoetin. Variables for the logistic regression model were age, weight, epoetin indication, baseline hemoglobin, epoetin dose, a history of diabetes mellitus, and concomitant medications.
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As a result of the continuous nature of the baseline hemoglobin values, a subanalysis logistic regression was also performed in order to make interpretation easier. Patients were categorized into the following groups:
- Group 0: baseline hemoglobin values below 10 g/dl
- Group 1: baseline hemoglobin values between 10 and 10.9 g/dl
- Group 2: baseline hemoglobin values between 11 and 11.9 g/dl
The subanalysis compared epoetin response rates in Groups 0 and 1 with the epoetin response rate in Group 2.
SAS version 9.1 (SAS Institute, Inc., 2004) was used to perform all statistical analyses in this study. A P value of less than .05 was considered significant.
We also evaluated the general usage trends of epoetin, including the overall hemoglobin response, monitoring of hemoglobin and ferritin levels, transferrin saturation, the starting dose, and dose adjustments.
Permission for this study was granted by the VA Medical Center’s institutional review board.
