Timing of FBC Repeat After Starting Haematinics
Repeat the full blood count (FBC) 3-4 weeks after starting haematinic supplementation for iron deficiency, or 3 months after starting vitamin B12 or folate replacement. 1
Iron Supplementation Monitoring
For iron therapy specifically:
- Repeat iron studies (including FBC) 3-4 weeks after the last dose of iron has been administered, particularly if the mean corpuscular volume (MCV) falls below 80 fL 1
- This timing allows assessment of response before deciding whether additional iron dosing is required 1
- In cancer patients receiving intravenous iron, studies assessed response at 8-16 weeks, with most showing significant haematological improvement by 12-16 weeks 1
Clinical context matters for iron monitoring:
- In chronic kidney disease (CKD) patients with GFR <30 ml/min per 1.73 m², haemoglobin should be checked at least every 3 months once on stable therapy 1
- After initial iron supplementation in CKD, reassess 2 weeks after the second dose (typically 8 weeks into treatment) to determine if further intervention is needed 1
Vitamin B12 and Folate Monitoring
For vitamin B12 or folate deficiency:
- Repeat measurements within 3 months after supplementation to verify normalization 1
- In diseases known to increase folate needs, measure every 3 months until stabilization, then annually 1
- After 3 months of oral vitamin B12 (2,000 mcg daily) or folate (1-5 mg daily), reassess to confirm correction 1
Important consideration: Vitamin B12 and folate levels may increase spontaneously during treatment of iron deficiency anaemia, even without direct supplementation 2. This phenomenon should be considered when interpreting follow-up results.
Practical Algorithm for Timing
Week 0: Start haematinic therapy
- Iron deficiency → oral or IV iron
- B12/folate deficiency → appropriate vitamin replacement
Week 3-4 (Iron only):
- Repeat FBC and iron studies 1
- If MCV <80 fL or inadequate response, consider additional iron dosing
- If adequate response, continue current regimen
Week 8-12 (All haematinics):
- For iron: Final assessment of response in most protocols 1
- For B12/folate: Interim check if clinically indicated
Month 3 (B12/Folate):
- Mandatory repeat to verify normalization 1
- Adjust or discontinue therapy based on results
Common Pitfalls to Avoid
- Don't wait too long for iron reassessment: Checking at 3-4 weeks prevents unnecessary continuation of ineffective therapy 1
- Don't assume combined deficiencies are corrected together: Iron deficiency may mask B12/folate deficiency haematologically; always recheck after iron correction 1
- Don't stop monitoring prematurely in chronic conditions: Patients with ongoing causes (CKD, cancer, malabsorption) require continued surveillance every 3 months 1
- Don't forget that response timing differs by route: IV iron shows faster response than oral supplementation, potentially allowing earlier reassessment 1