Added tag b/c directly relates to Q on NBME 12:
A 15-year-old girl is brought to the emergency department by her mother because of a 2-week history of heavy vaginal bleeding. Menarche was at the age of 14 years. Menses occur at irregular 21- to 35-day intervals and last 10 days with moderate flow. She has never been sexually active. She is not in distress. She is at the 55th percentile for height, 70th percentile for weight, and 60th percentile for BMI. Her temperature is 38°C (100.4°F), and blood pressure is 90/55 mm Hg. Examination shows pallor. Laboratory studies show a hemoglobin concentration of 9 g/dL, leukocyte count of 5500/mm³, and platelet count of 15,000/mm³. Which of the following is the most likely diagnosis?
Ans: Immune thrombocytopenic purpura
The diagnosis is one of exclusion after other potential causes of thrombocytopenia, such as viral infection, hematologic malignancy, and adverse effects of medication have been ruled out.