A 38-year-old woman presents with fatigue and dyspnea on exertion. On examination, she has pallor and glossitis. Her hemoglobin is 8.5 g/dL with microcytic hypochromic indices (MCV 68 fL, MCH 22 pg). Serum iron is low, TIBC is elevated, and ferritin is 12 ng/mL. Which investigation is most appropriate to confirm the diagnosis and identify the underlying etiology?

## Clinical Context The patient presents with classic features of iron deficiency anemia (IDA): microcytic hypochromic anemia with low serum iron, elevated TIBC, and low ferritin. While these investigations confirm iron deficiency, identifying the **source of blood loss** is essential for proper management. ## Why Upper GI Endoscopy is Correct **Key Point:** In iron deficiency anemia, once iron deficiency is biochemically confirmed, the next step is to identify the bleeding source. In women of reproductive age, menorrhagia is common, but GI bleeding (peptic ulcer disease, gastric cancer, celiac disease) must be excluded. **High-Yield:** The investigation of choice for suspected GI bleeding in IDA is **upper GI endoscopy** (± lower GI colonoscopy if upper endoscopy is negative). This is the gold standard for identifying mucosal lesions, ulcers, and malignancy. **Clinical Pearl:** In postmenopausal women and all men with IDA, GI source identification is mandatory before attributing anemia to other causes. Upper endoscopy has both diagnostic and therapeutic capability (e.g., hemostasis of bleeding ulcers). ## Investigation Hierarchy in IDA | Step | Investigation | Purpose | |------|---------------|----------| | 1 | CBC with indices, reticulocyte count | Confirm microcytic anemia | | 2 | Iron studies (serum iron, TIBC, ferritin) | Confirm iron deficiency | | 3 | **Upper GI endoscopy** | **Identify bleeding source** | | 4 | Lower GI colonoscopy | If upper endoscopy negative | | 5 | Celiac serology, fecal occult blood | Additional workup if needed | ## Why Peripheral Blood Smear Is Insufficient While a smear will show microcytic hypochromic RBCs and confirm morphologic iron deficiency, it does **not identify the etiology** (bleeding source). It is a confirmatory test for the anemia type, not for the cause.