A 77 year-old woman underwent elective laser lithotripsy and stenting for left nephrolithiasis. Two days later, she presents to the emergency department with diaphoresis and dizziness. She is found to be tachycardic and hypotensive. Her labs reveal a platelet count of 40 x 109/L. You are asked to see her to evaluate her thrombocytopenia. When you interview her, she is complaining of difficulty breathing and abdominal discomfort. You learn that she has been previously well with the exception of a history of hypertension and gout. She denies a past history of thrombocytopenia. There is no family history of thrombocytopenia or other hematological disorders. She denies alcohol intake. She is not a smoker. She is taking hydrochlorothiazide and allopurinol at home, and has no known drug allergies.