Review Question - QID 210726

A 27-year-old college student presents to his physician for constant fatigue. The patient states that for the past several weeks he has felt oddly fatigued and has struggled to complete his work. He is a foreign exchange student and is concerned he will fail out of his academic program. He has experienced some occasional nausea and vomiting which has caused him to lose weight. The patient is a 1st-year college student, drinks alcohol regularly, smokes marijuana, and has unprotected sex with multiple partners. His temperature is 99.5°F (37.5°C), blood pressure is 127/68 mmHg, pulse is 90/min, respirations are 17/min, and oxygen saturation is 98% on room air. Laboratory values are ordered as seen below.

Serum:
Na+: 139 mEq/L
Cl-: 100 mEq/L
K+: 4.3 mEq/L
HCO3-: 25 mEq/L
BUN: 20 mg/dL
Glucose: 99 mg/dL
Creatinine: 1.1 mg/dL
Ca2+: 10.2 mg/dL
Total bilirubin: 2.0 mg/dL
AST: 1,085 U/L
ALT: 1,292 U/L

Urine
Color: Amber/brown
Marijuana: Positive
Amphetamines: Positive
Cocaine: Positive

The patient refuses an examination of his genitals. Which of the following is the most appropriate diagnostic test?