USMLE Question #610: Real Exam Question with Answer & Explanation

A 40-year-old male comes to the emergency department due to a two-week history of a productive cough that is occasionally associated with blood. He has had similar episodes in the past. Vitals reveal a blood pressure of 140/80 mmHg, a heart rate of 75/min, a temperature of 37.6°C (99 6°F) and a respiratory rate of 16/ min. Oxygen saturation is 90% on room air. Laboratory results are as follows: Complete blood count - Hemoglobin 11.8 g/dL - Hematocrit 35.4% Mean Corpuscular Volume 85 ֲ μmֲ3 Leukocytes10,000/mmֲ3 - Differential: Neutrophils 60% Bands 3% Lymphocytes 25% Monocytes 7% Eosinophils 3%, Liver function studies - Alanine aminotransferase " 15 U/L Aspartate aminotransferase " 90 U/L Serum chemistry Creatinine " 1.5 mg/dL Blood urea nitrogen " 23 mg/dL - Urinalysis - blood, red blood cell casts. + The most likely other finding in this patient's serum is