A 67-year-old man presents to the primary care clinic reporting progressively worsening fa… — USMLE Step 2 CK

A $67$ -year-old man presents to the primary care clinic reporting progressively worsening fatigue and dyspnea on exertion over the past $3$ months. He denies any chest pain, orthopnea, or recent cough. He has a past medical history of hypertension and hyperlipidemia. His medications include lisinopril and atorvastatin. Vital signs show a blood pressure of $135/82$ mmHg, pulse of $92$ /min, and respiratory rate of $16$ /min. Physical examination reveals pale conjunctivae but no jaundice, cyanosis, or peripheral edema. Cardiopulmonary examination is unremarkable. Digital rectal examination reveals brown stool; no palpable masses are present.

Laboratory studies:
Hemoglobin: $8.4$ g/dL
Hematocrit: $26\%$
Mean corpuscular volume: $72$ fL
Leukocyte count: $6,500$ /mm $^3$
Platelet count: $410,000$ /mm $^3$

Serum iron: $30$ $\mu$ g/dL
Total iron-binding capacity (TIBC): $450$ $\mu$ g/dL
Serum ferritin: $12$ ng/mL

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

Colonoscopy and esophagogastroduodenoscopyAnswer
B
Initiation of oral ferrous sulfate therapy
C
Fecal occult blood testing
D
Hemoglobin electrophoresis
E
Transthoracic echocardiography

Answer

Colonoscopy and esophagogastroduodenoscopy

The patient's laboratory results demonstrate a microcytic anemia with low serum iron, elevated total iron-binding capacity (TIBC), and most importantly, a low serum ferritin level. This profile is diagnostic of iron deficiency anemia (IDA). In adult men and postmenopausal women, the most common cause of IDA is chronic, occult gastrointestinal bleeding. Because gastrointestinal malignancies (such as colon cancer) can present insidiously with only IDA, these patients require prompt and definitive visualization of the upper and lower gastrointestinal tracts via colonoscopy and esophagogastroduodenoscopy (EGD) to locate the source of bleeding.

Step-by-Step Solution

Interpret the complete blood count (CBC).

The patient has a profound microcytic anemia (hemoglobin

8.4

g/dL, MCV

72

fL) with reactive thrombocytosis.

Identifying the type of anemia narrows the differential diagnosis.

Analyze the iron panel.

Low serum iron, low ferritin (

12

ng/mL), and high total iron-binding capacity (

450

\mu

g/dL) strongly confirm Iron Deficiency Anemia (IDA).

Distinguishes IDA from other causes of microcytosis like anemia of chronic disease or thalassemia.

Apply the diagnostic algorithm for IDA based on patient demographics.

In adult men and postmenopausal women, IDA is considered secondary to occult gastrointestinal blood loss until proven otherwise.

Gastrointestinal malignancies (e.g., colon cancer) frequently present with asymptomatic, chronic occult bleeding.

Determine the most appropriate intervention.

Endoscopic evaluation (colonoscopy and esophagogastroduodenoscopy) must be performed immediately.

Direct visualization is required to diagnose or definitively rule out a bleeding gastrointestinal source.

Key Concept

Unexplained iron deficiency anemia in adult men and postmenopausal women must be evaluated with bidirectional endoscopy (colonoscopy and esophagogastroduodenoscopy) to rule out occult gastrointestinal malignancy.

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