You are answering a USMLE-style medical question. Question: An otherwise healthy 49-year-old woman has a routine full blood count complete prior her elective cholecystectomy. The lab test results are as follows: Laboratory test Hemoglobin 12.1 g/dL Mean corpuscular volume (MCV) 85 μm3 Mean corpuscular hemoglobin concentration (MCHC) 47% Reticulocyte count 3.4 % White blood cell count 9700/mm3 Platelet count 229,000/mm3 A peripheral blood smear reveals spherocytes. The Coombs test is negative. The physical examination is remarkable for scleral icterus and moderate splenomegaly. Which of the following is the most appropriate diagnostic test of this patient’s underlying disorder? Options: A) Eosin-5-maleimide binding test B) Flow cytometry for CD55/CD59 C) Anti parvovirus B19 antibodies D) Liver function tests Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.