Kidney stones are known for causing some of the worst pain a person can feel, and they’re a regular sight in US emergency rooms and urology clinics. Many patients have more than one episode over their lifetime. The ICD-10 code for kidney stones is N20.0, Calculus of kidney. But stones move, and as they travel through the urinary tract, the code moves with them. Where the stone sits, and whether it’s blocking urine flow, decides which code goes on the claim.
Quick Facts: Kidney Stone ICD-10 Codes
| Item | Details |
|---|---|
| Stone in the kidney | N20.0, Calculus of kidney |
| Stone in the ureter | N20.1, Calculus of ureter |
| Stones in both | N20.2, Calculus of kidney with calculus of ureter |
| Site not specified | N20.9, Urinary calculus, unspecified |
| Stone with hydronephrosis | N13.2 (replaces N20 codes) |
| Bladder and urethra stones | N21.- |
| Renal colic, no stone confirmed | N23 |
| History of stones | Z87.442 |
| Inclusion terms for N20.0 | Nephrolithiasis NOS, renal stone, staghorn calculus |
| Laterality | None; N20 codes don’t specify right or left |
Start With Where the Stone Is
The N20 category sorts stones by location in the upper urinary tract. Radiology reports, usually from a CT scan, provide that detail, but the provider’s documentation drives the code.
N20.0: Kidney
N20.0 covers stones still inside the kidney. Its inclusion terms include nephrolithiasis NOS, renal calculus, renal stone, stone in kidney, and staghorn calculus. Staghorn stones are large, branching stones that fill much of the kidney’s collecting system.
N20.1: Ureter
Once a stone leaves the kidney and enters the ureter, the tube that drains urine to the bladder, the code changes to N20.1. This is where stones usually cause the sudden, severe pain patients describe.
N20.2: Both Sites
When imaging shows stones in both the kidney and the ureter, N20.2 captures them together. Don’t report N20.0 and N20.1 separately. N20.2 also counts as a complication or comorbidity when it’s a secondary diagnosis on inpatient claims.
N20.9: Unspecified
N20.9 applies when the provider documents “urinary calculus” without naming a location. It should be rare once imaging is done.
No Laterality, No Recurrence Code
Two details surprise many coders.
First, N20 codes don’t specify side. A stone in the left kidney and one in the right both code to N20.0. Bilateral kidney stones still use N20.0.
Second, ICD-10-CM has no separate code for recurrent kidney stones. When the provider documents “recurrent nephrolithiasis,” code the current stone by location. The recurrence belongs in the clinical note.
When a Stone Causes a Blockage
A stone that blocks urine flow can cause the kidney to swell, a condition called hydronephrosis. This changes the code entirely.
The N20 category has an Excludes1 note for calculus with hydronephrosis. Use N13.2, Hydronephrosis with renal and ureteral calculous obstruction, instead. Don’t report N20.0 or N20.1 with it. N13.2 covers both the stone and the swelling.
If the blockage also leads to infection with pus in the kidney, the condition is pyonephrosis, which codes to N13.6.
A Realistic Example
A 42-year-old arrives at the emergency department with severe left flank pain and vomiting. CT shows a 6 mm stone in the left proximal ureter with moderate hydronephrosis. The ED physician documents “obstructing left ureteral stone with hydronephrosis.” The correct code is N13.2.
Change one detail. Same patient, same stone, but no hydronephrosis on CT. Now the code is N20.1.
Stones Lower in the Urinary Tract
Stones in the bladder or urethra fall under category N21:
- N21.0: Calculus in bladder
- N21.1: Calculus in urethra
- N21.8: Other lower urinary tract calculus
- N21.9: Calculus of lower urinary tract, unspecified
Before the Stone Is Confirmed
Not every patient with stone-like pain gets a confirmed diagnosis on the first visit. Before imaging, the provider may document only symptoms.
- Renal colic: N23, Unspecified renal colic
- Flank pain: R10.A0 through R10.A3, new codes that took effect October 1, 2025, by side
- Blood in urine: R31.-, Hematuria
Once the stone is confirmed, these symptom codes usually drop off. Renal colic and flank pain are expected parts of a kidney stone, so they aren’t coded separately with N20 or N13.2 codes.
Stones Linked to Other Conditions
Some stones result from an underlying disease. Category N22, Calculus of urinary tract in diseases classified elsewhere, applies in these cases and requires the underlying condition to be coded first, such as gout.
Category N20 also includes calculous pyelonephritis, kidney inflammation caused by a stone. When a separate urinary tract infection is documented, add the infection code and an organism code if known.
After the Stone Is Gone
Once a stone has passed or been removed and no active stone remains, switch to Z87.442, Personal history of urinary calculi. This code helps explain follow-up imaging, preventive dietary counseling, or 24-hour urine testing.
Don’t use Z87.442 when a current stone is still present. Code the active stone instead.
Pre-Billing Checklist
- Where is the stone: kidney, ureter, both, bladder, or urethra?
- Is hydronephrosis documented? If so, use N13.2.
- Is infection present with obstruction? Consider N13.6.
- Has the stone been confirmed, or is this still renal colic?
- Is an underlying disease causing the stones?
- Has the stone passed? Switch to Z87.442.
The codes in this guide were valid throughout FY2026. The FY2027 code set took effect October 1, 2026, so confirm each code in your current encoder before submitting claims.
FAQs
What is the ICD-10 code for kidney stones?
A stone in the kidney codes to N20.0, Calculus of kidney. If the stone has moved into the ureter, use N20.1. Stones in both locations use N20.2.
What ICD-10 code is used for a kidney stone with hydronephrosis?
Use N13.2, Hydronephrosis with renal and ureteral calculous obstruction. Don’t add N20.0 or N20.1, since the N20 category excludes calculus with hydronephrosis.
Is there an ICD-10 code for bilateral kidney stones?
No separate code exists. N20 codes don’t include laterality, so bilateral kidney stones still code to N20.0. Document the side in the clinical note.
What is the ICD-10 code for a history of kidney stones?
Use Z87.442, Personal history of urinary calculi, once no active stone remains. If a current stone is present, code the active stone by location instead.