Association of iron isotopic composition of blood and iron parameters. Correlation of the iron isotopic composition of blood (δ⁵⁶Fe/⁵⁴Fe) with serum ferritin concentration at time of diagnosis in treated (A) and untreated (B) patients with hemochromatosis and with the amount of iron removed by phlebotomy during iron depletion therapy (C) and maintenance therapy (D). Solid lines represent linear regression analyses; bars in panel D represent means ± 1 SD.