In a 55-year-old man with low mean corpuscular hemoglobin (MCH 26 pg), low mean corpuscular hemoglobin concentration (MCHC 29.8 g/dL), elevated red‑cell distribution width (RDW 16.2 %) and normal red blood cell count, hemoglobin, and hematocrit, what is the likely diagnosis and appropriate next steps?

Likely Diagnosis: Iron Deficiency

This 55-year-old man has laboratory findings highly suggestive of iron deficiency, and the next critical step is to measure serum ferritin to confirm the diagnosis, followed by comprehensive gastrointestinal evaluation to identify the source of iron loss.

Understanding the Laboratory Pattern

The combination of low MCH (26 pg), low MCHC (29.8 g/dL), and elevated RDW (16.2%) with normal RBC count, hemoglobin, and hematocrit represents early or evolving iron deficiency 1. This pattern indicates:

• Hypochromic cells (low MCH and MCHC): Red cells contain less hemoglobin than normal, characteristic of iron deficiency
• Increased anisocytosis (elevated RDW): Reflects a mixed population of normal older cells and newer iron-deficient cells
• Preserved cell count: Suggests the bone marrow is still producing adequate numbers of RBCs, but they are iron-deficient

The elevated RDW is particularly significant—RDW >17.1 strongly suggests iron deficiency 2, and your patient's value of 16.2% is approaching this threshold. The morphologic approach based on red cell indices classifies this as evolving microcytic anemia 3.

Immediate Diagnostic Steps

1. Confirm Iron Deficiency

Order serum ferritin immediately 1:

• Ferritin <30 μg/L confirms absolute iron deficiency 1, 4
• Ferritin <15 μg/L is diagnostic with 99% specificity 4
• If ferritin is 30-100 μg/L, consider transferrin saturation (<20% suggests iron deficiency) 1, 5
• Ferritin >100 μg/L makes iron deficiency unlikely unless inflammation is present 1

Additional helpful tests:

• Transferrin saturation <15-20% supports iron deficiency 3
• Total iron-binding capacity (TIBC) - typically elevated in iron deficiency 3

2. Rule Out Combined Deficiency

The elevated RDW can indicate combined iron and folate/B12 deficiency, which may mask typical microcytosis 1. Consider checking:

• Vitamin B12 level
• Folate level
• Peripheral blood smear review

Critical Next Step: Identify the Source

In a 55-year-old man, iron deficiency is gastrointestinal blood loss until proven otherwise 1. This age group has significant risk for occult malignancy.

Mandatory GI Evaluation

All men with confirmed iron deficiency require bidirectional endoscopy 1:

1. Upper endoscopy with small bowel biopsies:

   • Identifies gastric cancer, peptic ulcer disease, angiodysplasia
   • Small bowel biopsies are mandatory—2-3% of iron deficiency is from celiac disease 1
   • Expected to reveal a cause in 30-50% of cases 1

2. Colonoscopy or barium enema:

   • Essential to exclude colorectal cancer/polyps
   • Dual pathology occurs in ~10% of cases, so complete both upper and lower evaluation even if one is positive 1
   • In elderly patients, colon investigation is often more productive 1

Additional History Points to Elicit

• NSAID/aspirin use: Common cause of occult GI bleeding 1—stop if possible
• Dietary history: Borderline deficient diets are common but should not preclude full GI workup 1
• Family history: Thalassemia, hereditary hemorrhagic telangiectasia, bleeding disorders 1
• GI symptoms: Document but note they rarely correlate with findings 1

Common Pitfall to Avoid

Do not assume dietary insufficiency or attribute findings to "normal aging" without complete evaluation. Even mild iron deficiency in a 55-year-old man warrants full investigation, as the degree of anemia does not correlate with the seriousness of underlying pathology 1. Asymptomatic gastric and colonic carcinomas commonly present with iron deficiency 1.

If Ferritin Results Are Equivocal

Consider a therapeutic trial of oral iron (ferrous sulfate 325 mg daily for 2-3 weeks). A hemoglobin rise ≥10 g/L within 2 weeks strongly suggests absolute iron deficiency, even with equivocal iron studies 4. However, this should not delay GI investigation in this demographic.

Differential Considerations

While iron deficiency is most likely, also consider:

• Thalassemia trait: Typically shows elevated RBC count (not present here) and microcytosis out of proportion to anemia 1
• Anemia of chronic disease: Can present with microcytosis, but ferritin is usually >100 μg/L 3, 1
• Early combined deficiency: The elevated RDW supports this possibility 1