Immature Reticulocyte Fraction after Iron Therapy for Iron Deficiency Anemia.

Background: Automated counting of reticulocyte introduced new reticulocyte parameters such as immature reticulocyte fraction(IRF). IRF is thought to be more sensitive than absolute or corrected reticulocyte count for detecting recovery of bone marrow function. The aim of this study is to assess the role of IRF for predicting the response of therapy after treatment of iron deficiency anemia.

Methods: Patients with previously untreated iron deficiency anemia (blood hemoglobin < 10.0g/dL and serum ferritin < 10ng/mL) were enrolled into this study. On the 8th day of iron therapy, Complete blood count(CBC) with reticulocyte count and IRF was assessed by RAM-1 reticulocyte autoanalyzer(Sysmex. Tokyo, Japan). IRF was defined as sum of the reticulocyte fraction of high-fluorescence intensity regions plus the fraction of middle fluorescence intensity regions. After 1 month of iron therapy, CBC was reassessed to evaluate the response of iron therapy. The correlation of the 8th day IRF and the change of hemoglobin level after 4 weeks of therapy was evaluated. The 8th day corrected reticulcyte count was also evaluated.

Results: From Jan. 2001 to May 2003, 27 patients with iron deficiency anemia (3 men and 24 women) entered into this study. We evaluated 21 patients, excluding 6 patients who were lost to follow-up or refused blood sampling after 1 month of iron therapy. The range of pretreatment hemoglobin level was 3.3–9.7g/dL (median 7.5/dL). The 8th day IRF was 0.06–0.39(median 0.15). Ten patients had the low IRF (IRF ≤ 0.15). Four of them (40%) had their hemoglobin level increased by more than 3g/dL. On the other side, 11 patients had high IRF (IRF > 0.15) and 10 of them (91%) had their hemoglobin level increased by more than 3 g/dL. This difference was significant (P=0.024). However, the 8th day IRF was not correlated with the change of hemoglobin as strongly as the 8th day corrected reticulocyte count (Pearson coefficient 0.420 vs 0.693).

Conclusion: For the patients with iron deficiency anemia, the 8th day of treatment IRF correlates with the response of iron treatment, but the 8th day of treatment corrected reticulocyte count has a stronger correlation.