Laboratory Testing After Iron Supplementation

Timing of Laboratory Assessment

The American Gastroenterological Association recommends checking CBC and iron parameters (ferritin and TSAT) at 8-10 weeks to assess response to oral iron supplementation 1
For intravenous iron, wait at least 4 weeks, preferably 4-8 weeks after the last infusion before checking iron parameters, as ferritin levels are falsely elevated immediately after IV iron administration 2, 3
Hemoglobin should increase by 1-2 g/dL within 4-8 weeks of therapy if treatment is effective 2

A complete blood count (CBC) should be obtained to assess hemoglobin, hematocrit, mean corpuscular volume (MCV), and red blood cell indices 2, 3
Serum ferritin should be evaluated to assess iron stores, with a target level >30 ng/mL in most patients and >100 ng/mL in chronic kidney disease 1, 2
Transferrin saturation (TSAT) should be calculated from serum iron and total iron-binding capacity (TSAT = serum iron/TIBC × 100) 2

If hemoglobin has not increased by 1-2 g/dL, investigate for occult blood loss, particularly gastrointestinal sources, and evaluate for other causes of anemia beyond iron deficiency 1, 3
If iron parameters remain low, continue iron supplementation, and ensure oral iron is taken on an empty stomach for optimal absorption 1, 4

Do not check iron parameters too soon after IV iron, as ferritin levels remain artificially elevated for at least 4 weeks after IV administration 2
Do not continue oral iron indefinitely without reassessment, as lack of response by 8-10 weeks indicates need for alternative approach 1

After correction of iron deficiency, re-evaluate iron parameters 1-2 times per year as part of routine follow-up, and for patients on regular iron therapy who have achieved target hemoglobin levels, check TSAT and ferritin at least every 3 months 2, 3, 5