The Addis count is a urine test measuring urinary casts over time. Urinary casts are cylindrical aggregations of particulate matter that form in the distal nephron, dislodge, and eventually pass into the urine, and hold medical significance as diagnostic and prognostic indicators of kidney disease.

The Addis count is named for Thomas Addis (July 27, 1881 - June 4, 1949), a physician-scientist who made important contributions to the understanding of how blood clots. He was a pioneer in the field of nephrology, the branch of internal medicine that deals with diseases of the kidney. Addis was the first to demonstrate that normal plasma could correct the defect in haemophilia.