A 35-year-old woman presents to the clinic reporting a two-week history of profound fatigue and breathlessness upon exertion. She also notes that her urine has appeared unusually dark over the past several days. The patient has no prior significant medical conditions and takes no daily medications. Her temperature is 37.2°C (99.0°F), blood pressure is 112/70 mmHg, pulse is 108/min, and respiratory rate is 18/min. Physical examination reveals noticeable yellowing of the sclerae, pale conjunctivae, and a palpable spleen tip 3 cm below the left costal margin. There is no abdominal tenderness.
Laboratory studies reveal the following:
| Test | Result | Reference Range |
|---|---|---|
| Hemoglobin | 7.6 g/dL | 12.0–15.5 g/dL |
| Mean corpuscular volume | 94 fL | 80–100 fL |
| Platelet count | 210,000/µL | 150,000–400,000/µL |
| Leukocyte count | 7,500/µL | 4,500–11,000/µL |
| Reticulocyte count | 8.2% | 0.5–1.5% |
| Total bilirubin | 3.8 mg/dL | 0.1–1.2 mg/dL |
| Direct bilirubin | 0.5 mg/dL | 0.0–0.3 mg/dL |
| Lactate dehydrogenase (LDH) | 680 U/L | 100–250 U/L |
| Haptoglobin | < 10 mg/dL | 40–200 mg/dL |
A peripheral blood smear demonstrates numerous dense, spherical red blood cells lacking central pallor.
Which of the following is the most appropriate next step in the evaluation of this patient's anemia?
- Direct antiglobulin testCevap
- BEosin-5-maleimide binding test
- CRight upper quadrant ultrasonography
- DMeasurement of serum ferritin and iron levels
- EFlow cytometry for CD55 and CD59