Relationship between serum EPO levels and hemoglobin concentration.

Linear regression analysis for the correlation between serum EPO levels and hemoglobin in reference subjects (upper diagram) and RA patients (lower diagram). Regression lines are shown as solid lines and the 95% confidence limits as dotted lines. Regression equations, coefficient of correlation (r), and degree of significance (P) are indicated. (●) Nonanemic subjects; (○) anemic subjects.