A 32-year-old woman with a history of systemic lupus erythematosus presents with fatigue, pallor, and shortness of breath on exertion. Laboratory tests reveal pancytopenia with a markedly low reticulocyte count. She reports a recent episode of a facial rash and joint pain. Which of the following is the most appropriate next step to determine if parvovirus B19 is the cause of her current condition?
