What was Dr. House's medical specialty before he led diagnostic medicine in House M.D.?

Dr. House's medical specialties in House M.D. are nephrology and infectious disease.

Gregory House is presented as a board-certified diagnostician whose formal expertise combines kidney medicine with the study and treatment of infections. Those fields help explain why he is especially interested in unusual systemic illnesses that affect multiple organs or resist straightforward diagnosis.

House's diagnostic department is fictional, but the specialties referenced in the series are real medical disciplines. Nephrology focuses on the kidneys and related conditions, while infectious disease concerns illnesses caused by pathogens and the complications they produce. House frequently draws on both areas when evaluating mysterious cases.

The answer is sometimes shortened to “diagnostic medicine,” but that describes House's hospital role rather than his underlying specialties. Cardiology, neurology, and oncology belong to other doctors or cases in the series and are not House's stated specialty combination.