27th February 2025

A 53-year-old man presents to the emergency department with lethargy, fevers, pain on walking and a new rash on his lower legs.

A 53-year-old man presents to the emergency department with lethargy, fevers, pain on walking and a new rash on his lower legs. There is no history of recent foreign travel.

A chest radiograph demonstrates hilar lymphadenopathy. Formal blood tests are not yet back, but a venous blood gas shows an ionised calcium raised at 1.46 mmol/L (reference range 1.15-1.33 mmol/L).

What is the most important investigation not to be missed?

Select the SINGLE most appropriate option from the list below. Select ONE option only.