Acute renal colic is a sudden, severe flank pain radiating from the costovertebral angle to the groin or testicle, usually caused by urinary tract obstruction from a stone and often accompanied by nausea and vomiting. Urolithiasis affects about 1 in 11 people in the U.S. and occurs when crystals move from the kidney and obstruct urinary flow, typically in the ureter. This leads to hydroureteronephrosis, the main cause of renal colic.