What is the workup for Iron Deficiency Anemia (IDA)?

Workup for Iron Deficiency Anemia (IDA)

The workup for iron deficiency anemia requires confirmation of iron deficiency through iron studies followed by investigation for underlying causes, particularly gastrointestinal pathologies in men and postmenopausal women, with gastroscopy and colonoscopy as first-line investigations. 1

Diagnosis Confirmation

Initial Blood Tests

• Complete blood count (CBC) with:
  • Hemoglobin (Hb) below the lower limit of normal for the laboratory 1
  • Mean corpuscular volume (MCV) - typically low (<80 fL) in IDA 2
  • Mean corpuscular hemoglobin (MCH) - typically low in IDA 2
  • Red cell distribution width (RDW) - typically elevated in IDA 2

Iron Studies

• Serum ferritin - single most useful marker for IDA 1
  • Low levels (<15 μg/L) strongly suggest iron deficiency 2
  • Note: Ferritin is an acute phase reactant and may be falsely normal in inflammatory conditions
• Additional iron parameters when ferritin is equivocal:
  • Transferrin saturation (TSAT) - typically low in IDA 2
  • Serum iron - typically low in IDA
  • Total iron binding capacity (TIBC) - typically elevated in IDA

Therapeutic Trial

• 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

Investigation for Underlying Causes

Initial Assessment

• Detailed history focusing on:
  • Dietary intake
  • Menstrual blood loss in premenopausal women
  • Gastrointestinal symptoms
  • Medication history (NSAIDs, anticoagulants)
  • Family history of gastrointestinal malignancy 1
• Urinalysis or urine microscopy to detect hematuria 1

Mandatory Testing

• Celiac disease screening - found in 3-5% of IDA cases 1
  • Serological testing (anti-tissue transglutaminase antibodies)
  • Or small bowel biopsy at time of gastroscopy

Endoscopic Evaluation

• Men and postmenopausal women: Bidirectional endoscopy (gastroscopy and colonoscopy) should be first-line investigations 1
  • Approximately one-third will have an underlying pathological abnormality 1
  • CT colonography is a reasonable alternative if colonoscopy is not suitable 1
• Premenopausal women: Endoscopic evaluation if:
  • Age >50 years
  • Family history of colorectal cancer
  • Gastrointestinal symptoms
  • Severe or recurrent anemia
  • No obvious gynecological cause 1

Further Investigations for Persistent/Recurrent IDA

• If bidirectional endoscopy is negative and IDA persists or recurs:
  • Small bowel evaluation:
    • Capsule endoscopy (preferred method) 1
    • CT/MR enterography as alternatives 1
  • Helicobacter pylori testing and eradication if present 1
  • Consider renal tract investigation 1

Treatment Approach

Iron Replacement Therapy (IRT)

• Should not be deferred while awaiting investigations unless colonoscopy is imminent 1
• Oral iron:
  • First-line: Ferrous sulfate, fumarate, or gluconate, one tablet daily 1
  • If not tolerated: Reduced dose (one tablet every other day) or alternative preparations 1
• Intravenous iron if:
  • Oral iron not tolerated
  • Poor response to oral therapy
  • Malabsorption present
  • Rapid correction needed 2

Monitoring Response

• Check hemoglobin after 2-4 weeks of therapy 2
• Expected rise: 2 g/dL after 3-4 weeks of supplementation 2
• Continue iron therapy for 3 months after correction of anemia to replenish stores 2
• Follow-up CBC at 3-month intervals for one year, then after another year 2

Common Pitfalls and Caveats

• Failure to investigate men and postmenopausal women with IDA for gastrointestinal malignancy
• Stopping iron therapy too soon (before stores are replenished)
• Overlooking celiac disease as a potential cause
• Not investigating persistent or recurrent IDA after negative initial endoscopy
• Misinterpreting ferritin levels in the context of inflammation (may be falsely normal)
• Faecal occult blood testing is not recommended in the investigation of IDA 1

Remember that IDA in men and postmenopausal women requires urgent investigation due to the significant risk of underlying gastrointestinal malignancy, even in the absence of specific symptoms 1.