What is the recommended approach to diagnose and manage iron deficiency anemia in adults?

Iron Deficiency Anemia: Diagnosis and Management

In adults with newly diagnosed iron deficiency anemia, confirm the diagnosis with serum ferritin (<30 μg/L without inflammation, <45 μg/L with inflammation), initiate iron replacement therapy, and simultaneously investigate the underlying cause—particularly with urgent bidirectional endoscopy in men and postmenopausal women to exclude gastrointestinal malignancy. 1

Diagnostic Approach

Confirm Iron Deficiency

• Serum ferritin is the single most useful diagnostic marker 1

  • <15 μg/L: Highly specific for iron deficiency (specificity 0.99) 1
  • <30 μg/L: Generally indicates low body iron stores in healthy individuals 1, 2
  • <45 μg/L: Optimal cutoff balancing sensitivity and specificity (specificity 0.92) 1
  • <100 ng/mL: Diagnostic threshold in patients with chronic inflammatory conditions 3

• Transferrin saturation <20% supports iron deficiency diagnosis, particularly when ferritin is equivocal (46-99 ng/mL) 1, 3

• Therapeutic trial: Hemoglobin rise ≥10 g/L within 2 weeks of iron therapy is highly suggestive of absolute iron deficiency, even with equivocal iron studies 1

Initial Investigations (All Patients)

• Urinalysis or urine microscopy to exclude urinary blood loss 1
• Celiac disease screening (serology or small bowel biopsy at gastroscopy)—found in 3-5% of IDA cases 1
• Helicobacter pylori testing (noninvasive) as a common cause of IDA 3

Risk Stratification for GI Investigation

High-risk patients requiring urgent bidirectional endoscopy (gastroscopy + colonoscopy): 1

• All men with IDA
• All postmenopausal women with IDA
• Approximately one-third have underlying GI pathology, including malignancy 1

Lower-risk patients (investigation may be deferred): 1

• Premenopausal women with obvious menstrual blood loss or recent pregnancy
• However, maintain low threshold for investigation if GI symptoms, family history of GI pathology, or age-related risk factors present

Non-anemic iron deficiency (ferritin low, hemoglobin normal): 1

• GI investigation generally not warranted in premenopausal women without other risk factors
• Low threshold for investigation in men, postmenopausal women, or those with GI symptoms

Management Strategy

Iron Replacement Therapy

First-line: Oral iron 2, 3, 4

• Ferrous sulfate 325 mg daily or on alternate days 2
• Alternate-day dosing improves absorption and reduces adverse effects 3
• Approximately 50% of patients experience decreased adherence due to gastrointestinal side effects 3
• Reassess response in 2-4 weeks: expect hemoglobin rise ≥10 g/L 1, 3

Indications for intravenous iron (preferred over oral): 2, 3, 4

• Oral iron intolerance or inadequate response after 2-4 weeks
• Impaired iron absorption (celiac disease, post-bariatric surgery, atrophic gastritis)
• Chronic inflammatory conditions (chronic kidney disease, heart failure, inflammatory bowel disease, cancer)
• Ongoing blood loss
• Second and third trimesters of pregnancy 2
• Heart failure patients: IV iron increases exercise capacity 3

Hypersensitivity to newer IV iron formulations is rare (<1%) 3

Common Pitfalls to Avoid

• Do not rely on ferritin alone in inflammatory conditions: Ferritin is an acute phase reactant and may appear falsely normal despite true iron deficiency 1. Use transferrin saturation or higher ferritin cutoffs (<100 ng/mL) 3

• Do not skip investigation in high-risk groups: Approximately one-third of men and postmenopausal women have underlying GI pathology, often malignancy presenting without specific symptoms 1

• Do not use blood transfusion as iron replacement: Transfusion does not provide adequate elemental iron and is reserved only for severe symptomatic anemia with hemodynamic instability 5, 4

• Do not forget to screen for celiac disease: This treatable cause is found in 3-5% of IDA cases and directly impacts iron absorption 1

Treat Underlying Causes

Identify and address the source of iron deficiency: 2, 3

• Menstrual bleeding (38% of reproductive-age women have iron deficiency)
• GI blood loss (NSAID use, inflammatory bowel disease 13-90% prevalence)
• Malabsorption (celiac disease, atrophic gastritis, H. pylori, post-bariatric surgery)
• Inadequate dietary intake
• Pregnancy (up to 84% in third trimester)