What is the diagnosis and management for an adult patient with anemia, normal folate and vitamin B12 levels, low hemoglobin, elevated red cell distribution width, and normal mean platelet volume?

Diagnosis: Iron Deficiency Anemia with Markedly Elevated RDW

This patient has iron deficiency anemia (IDA) requiring immediate serum ferritin measurement to confirm the diagnosis, followed by comprehensive gastrointestinal investigation to identify the source of blood loss. 1

Laboratory Interpretation

Your patient's results reveal a clear pattern:

• Hemoglobin 11.4 g/dL: This is anemia by WHO criteria (below 13.0 g/dL for men or 12.0 g/dL for non-pregnant women) 1
• MCHC 30.7 g/dL: Low MCHC indicates hypochromia, strongly suggesting iron deficiency 1
• RDW 55.5%: This is dramatically elevated (normal <14.5%), which is the most critical finding distinguishing IDA from other causes of microcytic anemia 2, 3, 4
• Folate 23.70 and B12 333: Both normal, effectively excluding megaloblastic anemia 1
• MPV 12.1 fL: Normal, no platelet disorder 5

The combination of hypochromia with markedly elevated RDW (55.5%) is pathognomonic for iron deficiency anemia and essentially excludes thalassemia trait, which typically presents with RDW ≤14.0%. 2, 3

Immediate Diagnostic Steps

Confirm Iron Deficiency

Order serum ferritin immediately—this is the single most powerful diagnostic test and must be obtained before proceeding. 1, 6, 2

Interpret ferritin as follows:

• <15 μg/L: Diagnostic of iron deficiency (99% specificity) 6, 2
• <30 μg/L: Indicates depleted iron stores 1, 6, 2
• <45 μg/L: Warrants full investigation, especially if inflammation present 6, 2
• >100-150 μg/L: Essentially excludes absolute iron deficiency 1, 2

Additional iron studies to order:

• Transferrin saturation (TfS <16% supports iron deficiency) 1
• C-reactive protein (to assess for inflammation that may elevate ferritin) 1

Investigation for Blood Loss Source

Once iron deficiency is confirmed, gastrointestinal investigation is mandatory at any level of anemia, as 60-70% of IDA patients have identifiable GI pathology. 1, 2, 5

Endoscopic Evaluation Sequence

1. Upper endoscopy first (reveals pathology in 30-50% of cases):

   • Obtain small bowel biopsies to screen for celiac disease (present in 2-3% of IDA patients) 2
   • Look for gastritis, ulcers, vascular malformations 1

2. Colonoscopy second:

   • Prioritize if patient is elderly (colonic pathology more likely) 2
   • Screen for colorectal cancer, polyps, inflammatory bowel disease 1

Critical pitfall: Do not assume dietary deficiency explains the anemia—full GI investigation is required even with poor dietary intake, as serious pathology may be missed. 2

Treatment Protocol

Iron Supplementation

Initiate oral ferrous sulfate 200 mg three times daily immediately, even before completing investigations. 2

• Continue for at least 3 months after hemoglobin normalizes to replenish iron stores 2
• Add ascorbic acid (vitamin C) to enhance absorption 2
• Alternative formulations (ferrous gluconate, ferrous fumarate) if ferrous sulfate not tolerated 2

Therapeutic Trial as Diagnostic Tool

A hemoglobin rise ≥10 g/L within 2 weeks is highly suggestive of absolute iron deficiency, even if initial iron studies are equivocal. 1, 6

Monitoring Strategy

• Recheck hemoglobin and red cell indices at 3-month intervals for one year, then again after a further year 2
• Provide additional oral iron if Hb or MCV falls below normal during follow-up 2
• Monitor for recurrence, as >50% of patients develop recurrent anemia within 1 year, often indicating ongoing intestinal inflammation or blood loss 1

Critical Pitfalls to Avoid

Do not overlook combined deficiencies: While your patient's B12 and folate are currently normal, the extremely elevated RDW (55.5%) may indicate coexisting deficiencies that could mask each other's typical MCV changes. 1, 2

Do not miss thalassemia trait: If ferritin is normal and MCV is disproportionately low relative to anemia severity, order hemoglobin electrophoresis to exclude thalassemia. However, with RDW of 55.5%, thalassemia is highly unlikely. 1, 2

Do not delay investigation based on patient age or sex: Investigation should be considered at any level of anemia in the presence of iron deficiency, though the case is stronger with more severe degrees as they are more likely to have serious underlying GI pathology. 1