Correlations between hemoglobin (Hb) and serum erythropoietin levels in IDA, ACD, and HS patients. Correlations between Hb and serum erythropoietin levels in IDA patients (R = –0.892, P = .001), ACD patients (R = 0.163, P = .372), and HS patients (R = 0.674, P = .04) as determined by Spearman rank correlation technique are shown. The regression line and the 95% confidence interval are plotted.