Urinary casts are cylinrical aggregations of particulate matter that form in the distal nephron, dislodge, and eventually pass into the urine. They form via precipitation of Tamm-Horsfall mucoprotein which is secreted by renal tubule cells, and sometimes also by albumin in conditions of proteinuria. Cast formation is pronounced in environments favoring protein denaturation and precipitation (low flow, concentrated salts, low pH). Unfortunately, Tamm-Horsfall protein is particularly susceptible to precipitation in these conditions.