An 18-month-old white boy is brought to his well-care visit by his parents, who are concerned that for the past month he has been less social and active. He has appeared weak and has refused to walk or play with his siblings. He has also had a decreased appetite and has lost about 2 kg. He has vomited several times but with no bile or blood.
The child’s last well care visit was at age 6 months. He has had no recent illnesses, fever, diarrhea, or rash. He has a history of pica; recently, he was found ingesting fibers from the living room carpet. There is no family history of neurological, GI, rheumatological, or hematological disease. His immunizations are up-to-date. His diet consists of whole milk (six 4-oz bottles per day) and jarred baby foods. Developmental milestones have been appropriate. He lives with his mother and father and 2 brothers who are healthy.
The child looks tired and pale. His weight is 8.9 kg (less than the 3rd percentile); height, 79 cm (10th percentile); and head circumference, 48.5 cm (50th percentile). Temperature is 36.9°C (98.4°F); heart rate, 160 beats per minute; respiration rate, 28 breaths per minute; blood pressure, 85/49 mm Hg; and oxygen saturation, 100% on room air. In addition to tachycardia, a 2/6 systolic ejection murmur is noted. Heart sounds are normal. He is mesocephalic and has clear sclerae, normal oral mucosa, and a supple neck. Chest and lungs are clear. Abdomen is soft with no organomegaly or masses. The skin on his palms and soles is also pale. He has no bruising or petechiae. He refuses to walk, but neurological findings are nonfocal.
Hemoglobin level is 2.7 g/dL. The white blood cell count is 8300/μL, with 13% segmented neutrophils and 79% lymphocytes; the platelet count is 597,000/μL. Mean corpuscular volume is 46 fL, red cell distribution width is 37%, and reticulocyte count is 2.2%. Results of a basic metabolic panel are normal. Transaminase, alkaline phosphatase, and bilirubin levels are also normal.
Which of the following would be the logical next step?
(Answer and discussion on next page.)