If hemoglobin (Hb) is marginally low, should iron levels be checked before starting iron supplements?

Management of Marginally Low Hemoglobin

When hemoglobin is marginally low, iron studies should be checked before starting iron supplementation to confirm iron deficiency and identify underlying causes.

Diagnostic Approach for Marginally Low Hemoglobin

• A complete iron panel should be ordered including serum ferritin, transferrin saturation, and C-reactive protein to confirm iron deficiency before starting supplementation 1
• Serum ferritin is the single most useful marker of iron deficiency anemia (IDA), with levels <30 μg/L generally indicating low body iron stores 1
• Transferrin saturation <20% suggests iron deficiency, even when ferritin appears normal 1
• C-reactive protein should be measured to exclude false-normal ferritin results due to inflammation 1, 2
• A good response to iron therapy (Hb rise ≥10 g/L within 2 weeks) is highly suggestive of iron deficiency, even with equivocal iron studies 1

Decision Algorithm for Iron Supplementation

When to Check Iron Studies First:

• All patients with marginally low hemoglobin should have iron studies performed 1
• This approach prevents unnecessary supplementation in those without true iron deficiency 2
• Iron studies help identify the underlying cause of anemia, which may require specific treatment 1

When to Start Iron Without Testing:

• There are no evidence-based scenarios where starting iron without testing is recommended in adults with marginally low hemoglobin 1, 3
• Even in high-risk populations (menstruating women, pregnancy), iron studies should guide therapy 3

Treatment Recommendations Based on Iron Studies

If Iron Deficiency Confirmed:

• Oral iron therapy should be initiated with 28-50 mg elemental iron daily or on alternate days 4, 3
• Intravenous iron should be considered for patients with:
  • Clinically active inflammatory bowel disease 1
  • Previous intolerance to oral iron 1
  • Hemoglobin below 10 g/dL 1
  • Need for erythropoiesis-stimulating agents 1

If Iron Studies Normal:

• Iron supplementation should not be initiated as it provides no benefit and may be harmful 2, 4
• Further investigation for other causes of anemia should be pursued 1

Monitoring Response to Treatment

• Hemoglobin and iron studies should be rechecked after 8-10 weeks of therapy 4
• Long-term follow-up with basic blood tests every 6-12 months is recommended for patients with recurrent iron deficiency 4
• Daily oral or intravenous iron supplementation with normal or high ferritin values is not recommended and potentially harmful 4

Common Pitfalls to Avoid

• Starting iron without confirming deficiency can mask underlying conditions requiring treatment 1, 3
• Failing to recognize that normal ferritin does not exclude iron deficiency in inflammatory states 2
• Not investigating the underlying cause of iron deficiency, which may include gastrointestinal malignancy, celiac disease, or chronic blood loss 3, 5
• Continuing iron supplementation despite normal or high ferritin levels 4
• Overlooking functional iron deficiency (normal ferritin, low transferrin saturation) which may not respond to oral iron 2

Remember that iron deficiency without anemia can still cause symptoms like fatigue and should be treated, but only after proper diagnosis through iron studies 4, 3.