When should a full blood count be repeated after initiating oral iron therapy for iron‑deficiency anemia?

Timing of Full Blood Count Repeat After Starting Oral Iron for Iron Deficiency Anemia

Repeat the full blood count (FBC) 2 weeks after starting oral iron therapy to assess early response, then monitor every 4 weeks until hemoglobin normalizes. 1

Initial Response Assessment at 2 Weeks

• The absence of a hemoglobin rise of at least 10 g/L after 2 weeks of daily oral iron therapy is strongly predictive of subsequent treatment failure (sensitivity 90.1%, specificity 79.3%), making this the critical early checkpoint. 1

• This 2-week assessment identifies patients who are non-compliant, have malabsorption, ongoing blood loss, or other causes of treatment failure that require switching to parenteral iron or further investigation. 1

Ongoing Monitoring Every 4 Weeks

• After confirming adequate early response at 2 weeks, continue monitoring hemoglobin every 4 weeks until it reaches the normal range. 1

• Hemoglobin should increase by 1-2 g/dL within 4-8 weeks of therapy if treatment is effective. 2

Iron Studies Timing (Not FBC)

While you asked about FBC timing, it's important to note that iron studies (ferritin, transferrin saturation) should not be repeated until 8-10 weeks after starting oral iron, as ferritin levels need this duration to accurately reflect iron store repletion. 1

• After intravenous iron, wait even longer—4-8 weeks minimum—as ferritin is falsely elevated immediately post-infusion. 2, 3

After Hemoglobin Normalization

• Once hemoglobin normalizes, continue oral iron for an additional 2-3 months to replenish iron stores, then monitor hemoglobin every 3 months for the first year. 1, 2

• Re-evaluate after one additional year, then only if anemia symptoms recur. 2

Common Pitfalls

• Do not wait longer than 2 weeks for the first FBC recheck—this delays identification of treatment failure and prolongs patient suffering. 1

• Do not check ferritin at 2 weeks—it takes 8-10 weeks to accurately reflect iron store repletion with oral therapy. 1

• Do not assume compliance without objective evidence—the 2-week hemoglobin check catches non-adherence early. 1