A 12-year-old girl recently diagnosed with idiopathic aplastic anemia is brought to the clinic for follow-up. Since her visit a week ago, the patient has developed red spots and bruising on her arms and legs. Laboratory evaluation reveals an absolute neutrophil count of 420 cells/mm³ and platelet count of 7,000/mm³. She is given a platelet transfusion. Toward the end of the transfusion, the patient develops a rash on her chest that spreads to the rest of the body. Temperature is 37.2 C (99.0 F), blood pressure is 110/82 mm Hg, pulse is 90/min, and respirations are 18/min. Pulse oximetry is 98% on room air. Oropharynx examination is normal. Lung examination is unremarkable. Skin examination reveals a diffuse, urticarial rash along the trunk and extremities, along with pinpoint, nonblanching, red macules and bruises at the extremities. The transfusion is stopped, and the patient receives diphenhydramine. Vital signs remain stable over the next hour, and the rash improves slightly. Which of the following is the best next step in evaluation of this patient's transfusion reaction?

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11ec25c8_d698_d5f4_bc81_e352776ef00c_MD0003_00 This hemodynamically stable patient developed isolated urticaria during a transfusion, which is consistent with an urticarial transfusion reaction. Urticarial transfusion reactions are common and typically mild. Pathogenesis involves histamine release due to preformed recipient IgE antibodies reacting against a soluble allergen in the donated plasma, or vice versa (ie, donor IgE against recipient allergen). Symptoms are limited to hives and/or itching and develop hours after transfusion initiation. In contrast, hives due to anaphylaxis typically occur within minutes of transfusion initiation and develop in conjunction with wheezing, angioedema, and/or hypotension. Management of an urticarial transfusion reaction includes immediate cessation of the transfusion and administration of diphenhydramine (ie, antihistamine) if urticaria is extensive. Diagnosis is confirmed if symptoms improve and no signs of anaphylaxis develop. The transfusion can then be resumed without additional evaluation. (Choice A) Transfusion-transmitted bacterial infection (TTBI) is an uncommon, severe complication of transfusion that presents with fever, chills, and hypotension from a contaminated blood product (most commonly platelets). Cultures should be obtained from the recipient as well as from the transfused product to identify the pathogen and potential source of infection, respectively. This patient has no symptoms of TTBI, and therefore testing is not warranted. (Choices B, D, and E) Acute hemolytic transfusion reaction is a rare but potentially fatal reaction caused by mismatched donor and recipient blood (ie, ABO incompatibility) due to clerical error. Classic symptoms include fever, flank pain, hypotension, and dark/pink urine (ie, hemoglobinuria), none of which are seen in this patient. Evaluation typically reveals positive direct antibody (Coombs) testing. In cases complicated by disseminated intravascular coagulation, schistocytes on peripheral blood smear and prolonged PT and PTT are also seen. This patient's petechiae (pinpoint, nonblanching macules) and ecchymoses are consistent with her established thrombocytopenia and were present prior to transfusion. Educational objective: Urticarial transfusion reactions are common and caused by preformed recipient IgE antibodies reacting against a soluble allergen in the donated plasma (or vice versa). Patients have isolated urticaria that improves with transfusion cessation and diphenhydramine administration. If no signs of anaphylaxis are present (eg, wheeze, angioedema, hypotension), the transfusion can be resumed without additional evaluation. References: Transfusion reactions. (http://www.ncbi.nlm.nih.gov/pubmed/29489247)

A 12-Year-Old Girl Recently Diagnosed with Idiopathic Aplastic Anemia Is