Question: The radiologist documented nephrolithiasis with staghorn calculi. What diagnosis code should I use? Washington Subscriber Answer: You should report 592.0 (Calculus of kidney). Nephrolithiasis means presence of kidney stones.Staghorn calculi are stones that occur in the renal pelvis and extend into calyces, which are collecting structures in the kidneys. The stones can develop branches that resemble stag horns.