Approach to a fever (over 2 months) Quiz: Ace Your Exams

A 14-year-old girl is referred to the emergency department by the pediatrician for a 10-day history of low-grade fevers. Parents report her only significant past medical history is intermittent asthma well controlled with as-needed albuterol. For the past month, parents have noticed a dry cough unresponsive to albuterol. She has been more fatigued lately and has lost 8 lbs. She is at the 54^th percentile for height and 30^th percentile for weight. They have had no recent travel. Immunizations are up to date. Temperature is 38.2°C (100.8°F), pulse is 105/min, respirations are 16/min, blood pressure is 110/78 mmHg, and oxygen saturation is 96% on room air. On physical examination, the patient appears pale but is alert and lying quietly in the hospital bed. There is a 2/6 systolic murmur heard best at the left sternal border. Lungs are clear to auscultation bilaterally and there is no increased work of breathing. Abdomen is soft, non-tender, with normoactive bowel sounds. Mild hepatosplenomegaly is appreciated. There is cervical, axillary, and inguinal lymphadenopathy. Blood work is obtained and shown below. Which of the following tests should be ordered next?

Laboratory value	Result
Leukocyte count	24.6/mm3
Hemoglobin	10.5 g/dL
Hematocrit	30.9%
Platelet count	122/mm3
Erythrocyte sedimentation rate (ESR)	38 mm/hr
Lactate dehydrogenase (LDH)	345  U/L