Dr. Gregory House practiced nephrology alongside infectious disease in House M.D.
House is introduced primarily as a diagnostician, but the character's listed medical specialties are infectious disease and nephrology. Nephrology is the medical specialty concerned with the kidneys, kidney function, and related disorders.
The combination helps explain why House is portrayed as comfortable with complex systemic illness rather than being limited to one organ or symptom. His diagnostic department investigates rare and unexplained cases, while his specialty background supplies additional expertise in kidney disease and infections.
Viewers sometimes answer neurology because Dr. Eric Foreman is a neurologist, or cardiology because other hospital physicians handle heart cases. Those are specialties of different characters. House's canonical combination is infectious disease and nephrology, with diagnosis serving as his broader clinical role.