Laboratory Monitoring After Initiating Ferrous Sulfate
Check hemoglobin within 4 weeks to assess initial response, then recheck complete iron studies (hemoglobin, ferritin, and transferrin saturation) at 3 months after starting ferrous sulfate therapy. 1, 2, 3
Initial Response Assessment (First 4 Weeks)
- Monitor hemoglobin at 4 weeks to confirm therapeutic response to oral iron supplementation. 1
- Expect hemoglobin to increase by 1-2 g/dL within 4-8 weeks if the patient is responding appropriately to therapy. 2, 3
- Early evaluation at this timepoint allows for rapid identification of non-responders who may require alternative therapy or further investigation. 3
Complete Iron Studies at 3 Months
- Recheck comprehensive iron parameters at 3 months, including hemoglobin, hematocrit, serum ferritin, and transferrin saturation (TSAT). 1, 2, 3
- This 3-month timepoint is critical to evaluate therapeutic response and assess reconstitution of iron reserves. 2, 3
- Target values at 3 months should include ferritin 100-200 μg/L and TSAT >20%. 3
Duration of Treatment
- Continue ferrous sulfate for approximately 3 months after hemoglobin normalization to ensure adequate replenishment of marrow iron stores. 1
- A common pitfall is stopping treatment as soon as hemoglobin normalizes—this leads to inadequate iron reserve replenishment and early recurrence of deficiency. 3
Long-Term Surveillance After Correction
- Monitor hemoglobin and red cell indices every 3 months during the first year after achieving normal values. 2, 3
- After the first year, surveillance should occur every 6-12 months for patients at risk of relapse. 3
Special Populations Requiring Modified Monitoring
Chronic Kidney Disease Patients
- For CKD patients on erythropoietin-stimulating agents (ESAs), check TSAT and ferritin monthly in patients not receiving IV iron, and every 3 months in patients receiving IV iron until target hemoglobin is reached. 1, 2
- After achieving target hemoglobin, check TSAT and ferritin at least every 3 months. 1, 2
Inflammatory Bowel Disease Patients
- Monitor every 3 months for at least one year after correction of anemia, as recurrence rates exceed 50% at one year. 3
Important Caveats
- Proton pump inhibitors significantly impair oral iron absorption—patients on omeprazole or similar medications may show suboptimal response (only 16% achieving normal hemoglobin rise of >2 g/dL at 3 months) and may require higher doses, longer duration, or IV iron therapy. 4
- If hemoglobin or ferritin fails to normalize at 3 months despite adequate therapy, investigate for ongoing blood loss, malabsorption, or other causes of treatment failure. 1
- Ferritin is an acute phase reactant and can be falsely elevated in inflammatory states—consider checking C-reactive protein when interpreting ferritin results. 2