During a scheduled wellness examination, a 72-year-old male mentions to his physician that… — USMLE Step 2 CK

During a scheduled wellness examination, a 72-year-old male mentions to his physician that his daily neighborhood walks have become increasingly difficult over the last three months due to profound fatigue. He has no prior history of cardiopulmonary disease and denies melena, hematochezia, changes in bowel habits, or abdominal pain. Vital signs are temperature $37.0^\circ\text{C}$ ( $98.6^\circ\text{F}$ ), blood pressure 135/82 mm Hg, pulse 86/min, and respirations 14/min. Physical examination demonstrates noticeable conjunctival pallor. The abdomen is soft and non-tender without hepatosplenomegaly.

Laboratory evaluation reveals the following:

Test	Result	Reference Range
Hemoglobin	9.1 g/dL	13.5-17.5 g/dL
Mean corpuscular volume (MCV)	73 fL	80-100 fL
Leukocyte count	6,500/mm $^3$	4,500-11,000/mm $^3$
Platelet count	410,000/mm $^3$	150,000-400,000/mm $^3$
Serum iron	25 $\mu$ g/dL	65-175 $\mu$ g/dL
Total iron-binding capacity (TIBC)	460 $\mu$ g/dL	250-400 $\mu$ g/dL
Serum ferritin	9 ng/mL	20-250 ng/mL

Which of the following is the most appropriate next step in management?

A
Initiation of oral ferrous sulfate and reassessment in 3 months
B
Hemoglobin electrophoresis
Referral for colonoscopy and esophagogastroduodenoscopyAnswer
D
Measurement of serum methylmalonic acid and homocysteine levels
E
Bone marrow aspiration and biopsy

Answer

Referral for colonoscopy and esophagogastroduodenoscopy is the correct next step to evaluate for gastrointestinal malignancy.

The correct answer is referral for colonoscopy and esophagogastroduodenoscopy. This patient presents with laboratory findings pathognomonic for iron deficiency anemia (microcytosis, low serum iron, high total iron-binding capacity, and low ferritin). In adult men and postmenopausal women, the most common and critical cause of iron deficiency is occult gastrointestinal blood loss. Because gastrointestinal malignancies (such as colorectal carcinoma) can present solely with iron deficiency anemia prior to the onset of bowel symptoms or overt bleeding, bidirectional endoscopy is mandatory to rule out cancer.

Step-by-Step Solution

Analyze the complete blood count and iron studies.

The patient has a microcytic anemia (MCV 73 fL) with low serum iron, high TIBC, and low ferritin (9 ng/mL).

To establish the specific etiology of the patient's anemia, which clearly indicates iron deficiency.

Determine the clinical significance of iron deficiency in this specific demographic.

In an elderly male, iron deficiency anemia is highly suspicious for chronic gastrointestinal blood loss.

To recognize that unlike in menstruating women, iron deficiency in older adults is rarely due to physiologic blood loss or pure dietary deficiency.

Select the appropriate diagnostic intervention.

Bidirectional gastrointestinal endoscopy (colonoscopy and esophagogastroduodenoscopy) is indicated.

To rule out occult gastrointestinal malignancies, such as colon cancer, which are the most critical, life-threatening causes of occult blood loss in this age group.

Key Concept

In adult males and postmenopausal females, new-onset iron deficiency anemia must be presumed to be caused by gastrointestinal bleeding (often occult malignancy) until proven otherwise, necessitating endoscopic evaluation.

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