A 28-year-old man of Southeast Asian descent presents to the primary care clinic complaining of mild, intermittent fatigue over the past six months. He has no other symptoms, and his past medical history is unremarkable. He follows a strict vegan diet and takes no supplements. Vital signs are within normal limits. Physical examination is notable only for mild conjunctival pallor. The physician suspects an underlying hematologic abnormality and plans a stepwise laboratory evaluation.
Arrange the following diagnostic laboratory tests in the most appropriate chronological sequence to definitively evaluate the etiology of this patient's presentation, from initial screening to definitive confirmation.
- 1Complete blood count (CBC) with red blood cell indices
- 2Serum iron, total iron-binding capacity (TIBC), and ferritin
- 3Hemoglobin electrophoresis or high-performance liquid chromatography (HPLC)
- 4Alpha-globin gene molecular analysis (DNA testing)
Answer
The correct sequence is: Complete blood count (CBC), followed by Iron studies (ferritin, iron, TIBC), followed by Hemoglobin electrophoresis, and finally Alpha-globin gene molecular analysis.
The correct diagnostic sequence begins with a complete blood count (CBC) to confirm the presence of anemia and determine the mean corpuscular volume (MCV). Given this patient's high risk for microcytic anemia (vegan diet and Southeast Asian descent), the MCV will likely be low. The next crucial step is ordering iron studies (ferritin, serum iron, TIBC). Iron deficiency must be explicitly ruled out or treated before proceeding further, as it is not only the most common cause of microcytosis but also actively suppresses Hemoglobin A2 synthesis. If hemoglobin electrophoresis is performed while a patient is iron-deficient, a concurrent beta-thalassemia trait may be missed due to falsely lowered HbA2 levels. Once iron stores are confirmed to be normal, hemoglobin electrophoresis or HPLC is performed to assess for beta-thalassemia trait or other structural variants. If the electrophoresis pattern is completely normal but unexplained microcytosis persists, the final diagnostic step is alpha-globin gene molecular analysis. Alpha-thalassemia trait typically presents with a normal electrophoresis pattern in adults, requiring DNA testing for definitive confirmation.
Step-by-Step Solution
Key Concept
Diagnostic sequencing of microcytic anemia requires ruling out iron deficiency before interpreting hemoglobin electrophoresis, followed by genetic testing if alpha-thalassemia is suspected.
Estimated Time:1m 30s