A 24-year-old woman, G1P0 at 10 weeks gestation, comes to the clinic for her first prenatal visit. She feels well and has no significant past medical history. She is of Southeast Asian descent. She takes a daily prenatal vitamin. Blood pressure is 112/68 mmHg, and pulse is 78/min. Physical examination shows no abnormalities.
Laboratory studies reveal the following:
| Test | Result | Normal Range |
|---|---|---|
| Hemoglobin | 10.4 g/dL | 12.0–15.5 g/dL |
| Mean corpuscular volume (MCV) | 68 fL | 80–100 fL |
| Red blood cell (RBC) count | 5.6 million/mm | 4.1–5.1 million/mm |
| Red cell distribution width (RDW) | 12.8% | 11.5%–14.5% |
| Serum iron | 110 g/dL | 60–170 g/dL |
| Total iron-binding capacity (TIBC) | 310 g/dL | 240–450 g/dL |
| Serum ferritin | 125 ng/mL | 15–200 ng/mL |
Hemoglobin electrophoresis demonstrates:
- Hemoglobin A: 97.5%
- Hemoglobin A2: 2.0%
- Hemoglobin F: 0.5%
Which of the following is the most appropriate next step in management?
- Evaluate the patient's partner with a complete blood countAnswer
- BReassure the patient that these findings are secondary to normal pregnancy changes
- CPrescribe a therapeutic trial of oral ferrous sulfate
- DPerform molecular genetic testing of the patient's alpha-globin genes
- ERecommend immediate chorionic villus sampling
Answer
Evaluate the patient's partner with a complete blood count
The correct answer is to evaluate the patient's partner with a complete blood count (CBC). This patient presents with a microcytic anemia (hemoglobin 10.4 g/dL, MCV 68 fL). The initial step in evaluating microcytic anemia is an iron panel. This patient has normal iron studies (ferritin 125 ng/mL), effectively ruling out iron deficiency anemia. The combination of microcytosis, normal iron studies, elevated RBC count, and a normal red cell distribution width (RDW) is highly suggestive of thalassemia trait. Next, hemoglobin electrophoresis is performed to differentiate between alpha and beta-thalassemia trait. Beta-thalassemia trait is characterized by elevated Hemoglobin A2 (>3.5%). This patient's normal hemoglobin electrophoresis (HbA2 2.0%) rules out beta-thalassemia trait, leaving alpha-thalassemia trait as the presumed diagnosis.
Because this patient is of Southeast Asian descent, she is at high risk of carrying a 'cis' deletion of two alpha-globin genes (). If her partner also carries a two-gene deletion, the fetus is at a 25% risk of inheriting a four-gene deletion (), leading to hemoglobin Barts and hydrops fetalis. To assess this risk, the most appropriate and cost-effective next step is to evaluate the partner's MCV with a simple CBC. If the partner's MCV is normal, the fetus is not at risk for hydrops fetalis, and further testing is unnecessary.
Because this patient is of Southeast Asian descent, she is at high risk of carrying a 'cis' deletion of two alpha-globin genes (). If her partner also carries a two-gene deletion, the fetus is at a 25% risk of inheriting a four-gene deletion (), leading to hemoglobin Barts and hydrops fetalis. To assess this risk, the most appropriate and cost-effective next step is to evaluate the partner's MCV with a simple CBC. If the partner's MCV is normal, the fetus is not at risk for hydrops fetalis, and further testing is unnecessary.
Step-by-Step Solution
Key Concept
In a pregnant patient with suspected alpha-thalassemia trait (microcytic anemia, normal iron studies, normal hemoglobin electrophoresis), the most appropriate next step is to screen the partner with a complete blood count to assess the risk of hemoglobin Barts hydrops fetalis.
Estimated Time:1m 30s