The adoptive mother of a 5-month-old child born in another country brings the child to the nurse practitioner's office. The child's medical history is unknown. The mother states that over the past 2 days, the child has been experiencing frequent bouts of crying that are unrelieved by holding. The mother reports that the child's hands and feet are slightly swollen during these episodes. On examination, the child's temperature is 101°F with mild splenomegaly. Sickle cell disease is suspected. This diagnosis may be confirmed by:

Rationale: A. The Sickledex test is a rapid screening tool for sickle hemoglobin but cannot definitively diagnose sickle cell disease. B. A complete blood count (CBC) may show anemia or other hematologic abnormalities but cannot confirm the specific hemoglobin type. C. Hemoglobin electrophoresis is the definitive test to diagnose sickle cell disease. It identifies the specific types of hemoglobin present (e.g., HbS, HbA, HbF) and distinguishes between sickle cell trait and sickle cell disease. D. The sickle cell solubility test can indicate the presence of HbS but cannot differentiate between trait and disease and is therefore not diagnostic.