Monitoring Iron Ferritin for Iron Deficiency Anemia (IDA)
Laboratory evaluation for IDA should include complete blood count (CBC) and iron parameters (ferritin, transferrin saturation) 4-8 weeks after iron supplementation, with a goal ferritin of at least 50 ng/mL in the absence of inflammation. 1
Initial Diagnostic Parameters
- Serum ferritin is the most powerful test for diagnosing iron deficiency, with a level <12 μg/dL being diagnostic of iron deficiency in the absence of inflammation 1
- In patients without clinical, endoscopic, or biochemical evidence of active disease, serum ferritin <30 μg/L is an appropriate criterion for the diagnosis of iron deficiency anemia 1
- In the presence of inflammation, a serum ferritin up to 100 μg/L may still be consistent with iron deficiency 1
- Transferrin saturation (TSAT) <20% has high sensitivity for diagnosing absolute or functional iron deficiency 1
Monitoring Protocol After Iron Supplementation
Timing of Laboratory Assessment
- Laboratory evaluation should be performed 4-8 weeks after the last iron infusion 1
- Iron parameters should NOT be evaluated within 4 weeks of total dose iron infusion, as circulating iron interferes with the assay leading to inaccurate results 1
- Hemoglobin concentrations should increase within 1-2 weeks of treatment and should increase by 1-2 g/dL within 4-8 weeks of therapy 1
Parameters to Monitor
- Complete blood count (CBC) 1
- Serum ferritin 1
- Transferrin saturation (TSAT) - calculated by dividing serum iron by total iron binding capacity (TIBC) 1
- In the absence of inflammation, the goal ferritin is at least 50 ng/mL, regardless of sex at birth 1
Frequency of Monitoring
- For patients in remission or with mild disease, measurements should be performed every 6-12 months 1
- For outpatients with active disease, measurements should be performed at least every 3 months 1
- Patients with recurrent blood loss require more frequent and aggressive laboratory monitoring 1
Special Considerations
Inflammatory Conditions
- In the presence of inflammation, ferritin may be elevated due to its acute phase reactivity while TSAT is low 1
- In inflammatory conditions, a serum ferritin >100 μg/L and transferrin saturation <20% are diagnostic criteria for anemia of chronic disease 1
- If serum ferritin is between 30-100 μg/L with inflammation present, a combination of true iron deficiency and anemia of chronic disease is likely 1
Alternative Monitoring Parameters
Soluble transferrin receptor (sTfR) is more sensitive in patients with inflammatory conditions where ferritin is unreliable 1
Reticulocyte hemoglobin content (CHr) or reticulocyte hemoglobin equivalent (RET-He) can be used as direct assessments of functional iron availability 1, 2
Monitoring After IV Iron Therapy
- After successful treatment of iron deficiency anemia with intravenous iron, re-treatment should be initiated as soon as serum ferritin drops below 100 μg/L or hemoglobin below 120 g/L (women) or 130 g/L (men) 1
- For patients with ongoing losses (heavy menstrual bleeding, inflammatory bowel disease) or conditions with inhibited iron absorption (bariatric surgery, celiac disease), multiple administrations may be necessary 1
- Patients with an inappropriate response to IV iron should be evaluated for ongoing blood loss or alternative diagnoses 1
Pitfalls to Avoid
- Do not measure iron parameters within 4 weeks of IV iron administration as this leads to inaccurate results 1
- Do not rely solely on ferritin in inflammatory conditions; consider TSAT or alternative markers like sTfR 1
- Do not assume a normal MCV excludes iron deficiency, as microcytosis may be absent in combined deficiencies (e.g., with folate deficiency) 1
- Do not overlook the need for investigation of the underlying cause of iron deficiency, especially in adult men and post-menopausal women 1