Kidney Stone ICD-10 Code: Billing and Coding Guide

Kidney stones, clinically termed nephrolithiasis or urolithiasis, are among the most frequently billed diagnoses in urology and nephrology. They are also among the most frequently miscoded.

The ICD-10-CM framework for kidney stones is location-driven. The correct code depends on where imaging confirms the stone sits, such as the kidney only, the ureter only, both, or the lower urinary tract. One wrong assumption about location triggers an automatic denial.

This guide covers every billable kidney stone ICD-10 code, the Excludes1 rules that drive most claim rejections, and the documentation requirements for each code. It also explains sequencing rules, CPT pairings for stone procedures, and the most common denial patterns in urology and nephrology billing. Reviewing a complete list of ICD-10 codes for Nephrology billing helps teams verify clinical location rules before claims are submitted to the payer clearinghouse.

Kidney Stone ICD-10 Quick Reference Card — 2026

Primary Kidney Stone Codes (N20 Family)
Code	Name	Key Rule
N20.0	Calculus of kidney	Stone in kidney only; hydronephrosis must be absent
N20.1	Calculus of ureter	Stone in ureter only; hydronephrosis must be absent
N20.2	Calculus of kidney with calculus of ureter	Stones in both; hydronephrosis must be absent
N20.9	Urinary calculus, unspecified	Use only when location not documented

Obstruction and Complication Codes
Code	Name	Key Rule
N13.2	Hydronephrosis with calculous obstruction	Replaces all N20.x codes when hydronephrosis is confirmed
N13.6	Pyonephrosis	Stone obstruction plus documented infection
N23	Unspecified renal colic	Use when stone not yet confirmed on imaging

Lower Urinary Tract Stones
Code	Name	Key Rule
N21.0	Calculus in bladder	Stone in bladder, confirmed by imaging or cystoscopy
N21.1	Calculus in urethra	Stone in urethra
N21.9	Lower urinary tract calculus, unspecified	Use when location within lower tract is not specified

Critical Rules
Excludes1	N20.x + N13.2	Never bill together for the same stone episode. N13.2 is a combination code.
Laterality	No left/right subcodes	Document side in chart; ICD-10 code does not change.
Imaging	Required before N20.x	CT, ultrasound, or KUB must confirm stone location before coding.
CPT bundling	52352 + 52353	Do not bill 52352 for fragment removal from the same lasered stone.

What Is the ICD-10 Code for Kidney Stones?

The primary ICD-10 code for a kidney stone is N20.0 — Calculus of the kidney. It is a billable code used when imaging confirms a stone located in the kidney without hydronephrosis.

N20.0 sits within the N20 parent category (Calculus of kidney and ureter), under Chapter 14 of ICD-10-CM. Use it only when imaging techniques like CT, ultrasound, or KUB X-ray confirm the stone location.

N20.0 is not always the right code. When a stone migrates to the ureter, N20.1 applies. When hydronephrosis is present, N13.2 replaces all N20 codes. Defaulting to N20.0 without confirming the location is a coding quality failure. Relying on an updated nephrology billing guide allows coding teams to track these anatomical guidelines and establish proper diagnostic parameters within the medical record.

Important: ICD-10-CM has no laterality subcodes for kidney stones. N20.0 does not distinguish left from right. Document the side in the medical record for clinical clarity, but the ICD-10 kidney stone code does not change.

Complete Kidney Stone ICD-10 Code Table — 2026 Edition

The 2026 ICD-10-CM edition retains all urolithiasis codes from the prior edition with no deletions or additions to the N20 family. ICD-10 kidney stone codes are organized by anatomical location.

The N20 Code Family: Calculus of Kidney and Ureter

Use N20 codes when imaging confirms a stone in the kidney, ureter, or both, and hydronephrosis is absent.

Code	Description	When to Use	Billable	Hydronephrosis?
N20	Calculus of kidney and ureter	Parent category — do not bill directly	No	N/A
N20.0	Calculus of kidney	Stone in kidney only, confirmed on imaging, no hydronephrosis present	Yes	Must be absent
N20.1	Calculus of ureter	Stone confirmed in ureter by imaging, no hydronephrosis	Yes	Must be absent
N20.2	Calculus of kidney with calculus of ureter	Stones confirmed in both kidney and ureter simultaneously	Yes	Must be absent
N20.9	Urinary calculus, unspecified	Stone confirmed but exact location not specified in imaging or documentation	Yes	Must be absent

The N13.2 Code: When Hydronephrosis Is Present

When a kidney or ureteral stone causes hydronephrosis, the correct code shifts entirely out of the N20 family. Use N13.2 — Hydronephrosis with renal and ureteral calculous obstruction.

N13.2 is a combination code. It captures both the stone and the hydronephrosis in a single code. Adding any N20 code alongside N13.2 for the same encounter violates the Excludes1 rule and triggers an automatic denial.

Code	Description	When to Use	Do Not Combine With
N13.2	Hydronephrosis with renal and ureteral calculous obstruction	Stone confirmed on imaging AND hydronephrosis is documented	N20.0, N20.1, N20.2, N20.9 (Excludes1)
N13.6	Pyonephrosis	Hydronephrosis with obstruction and documented infection	N20.x, N13.2

N23 — Unspecified Renal Colic

Use N23 — Unspecified renal colic when a patient presents with classic colic symptoms but imaging has not confirmed a stone at the time of coding.

N23 is an interim code. Once imaging confirms a stone and its location, replace N23 with the appropriate N20 or N13 code. Do not use N23 alongside a confirmed stone code on the same claim.

Code	Description	Use When	Replace With
N23	Unspecified renal colic	Colic symptoms present, stone not yet confirmed on imaging	N20.x or N13.2 once imaging confirms stone

N21 Codes — Calculus of Lower Urinary Tract

When a stone migrates fully into the bladder or urethra, use N21 codes. These are distinct from N20 codes and apply to different anatomical locations.

Code	Description	When to Use	Billable
N21.0	Calculus in bladder	Stone confirmed in bladder by imaging or cystoscopy	Yes
N21.1	Calculus in urethra	Stone confirmed in urethra	Yes
N21.8	Other lower urinary tract calculus	Calculus in other specified lower urinary tract site	Yes
N21.9	Calculus of lower urinary tract, unspecified	Lower urinary tract stone, exact site not specified	Yes

N22 — Calculus in Diseases Classified Elsewhere

Use N22 when a urinary calculus is directly caused by a systemic disease coded elsewhere. For example, hypercalciuria due to hyperparathyroidism or uric acid stones from gout. Code the underlying condition first. N22 is coded additionally.

Excludes1 Notes — The Rule That Drives Most Denials

The N20 parent category carries an Excludes1 note for N13.2. This is the most violated coding rule in kidney stone billing. Violating it does not produce a payer letter. It produces an automated scrubber rejection before the claim reaches a human reviewer.

Excludes1 vs. Excludes2

Note Type	What It Means	Both Codes Together?
Excludes1	The excluded condition cannot coexist with this code. ICD-10-CM language: “Not coded here.”	Never; automatic denial if combined
Excludes2	The excluded condition is not included in this code, but the patient can have both. ICD-10-CM language: “Not included here.”	Yes, if both conditions are documented and clinically distinct

What the Excludes1 Note Under N20 Excludes

The Excludes1 note applies to all N20 subcodes: N20.0, N20.1, N20.2, and N20.9. It excludes N13.2 (hydronephrosis with renal and ureteral calculous obstruction).

This means, if imaging shows a stone AND hydronephrosis, N13.2 is the only correct code. N20.x is excluded.

COMMON DENIAL SCENARIO A urologist documents a right ureteral stone with hydronephrosis on CT. The coder assigns N20.1 plus N13.2, reasoning that both findings are documented. The scrubber rejects: Excludes1 violation. The correct code is N13.2 alone. N13.2 is a combination code that already captures the stone and the hydronephrosis.

The Bilateral Stone Exception

One scenario where both N20.x and N13.2 may appear on the same claim is a bilateral stone encounter. For example, a nonobstructed left kidney stone ICD-10 code (N20.0) alongside a right ureteral stone with hydronephrosis (N13.2) in the same patient visit.

Per ICD-10-CM guidelines, coders may report N20.0 and N13.2 together when they describe stones on opposite sides of the body causing different clinical conditions. The Excludes1 rule applies to the same anatomical condition, not separate bilateral findings.

This distinction must be supported by imaging documentation clearly identifying left and right sides and distinct clinical conditions. Even then, some payer edits may reject the combination. Be prepared to appeal with the operative or imaging report.

Because managing these intricate multi-layered edits requires exceptional oversight, leading practices frequently cross-examine top nephrology billing services to find a partner capable of executing clean claims under complex bilateral parameters.

N20.0 vs. N20.1 vs. N13.2: Choosing the Right Code

These three codes account for the majority of kidney stone billing and the majority of coding errors. The decision tree is entirely imaging-driven.

Clinical Finding on Imaging	Correct Code	Do Not Use
Stone in kidney only, no hydronephrosis	N20.0	N13.2, N20.1, N20.9
Stone in ureter only, no hydronephrosis	N20.1	N13.2, N20.0, N20.9
Stones in both kidney and ureter, no hydronephrosis	N20.2	N20.0+N20.1 together, N13.2
Stone in kidney or ureter with confirmed hydronephrosis	N13.2	Any N20.x code (Excludes1)
Colic symptoms, stone not yet confirmed on imaging	N23	N20.x, N13.2
Stone location not specified in imaging or notes	N20.9	N20.0 or N20.1 without imaging support
Stone confirmed in bladder	N21.0	N20.0, N20.1

CODING TIP ICD-10-CM does not provide laterality subcodes for kidney stone ICD-10 codes. N20.0 covers both left and right kidney stones ICD-10. Document the affected side in the operative note and imaging report for clinical accuracy and payer audits. The ICD-10 code itself does not change.

Code Sequencing Rules

Selecting the right code is half the work. Sequencing it correctly completes the claim. Sequencing errors are among the most common compliance risks in kidney stone billing.

Outpatient Sequencing Rules

In outpatient settings, the first-listed diagnosis is the condition chiefly responsible for services rendered. Follow ICD-10-CM Section IV guidelines.

• If the patient presents for a known kidney stone and it is confirmed by imaging, code N20.x or N13.2 as first-listed.
• If colic is present but imaging is negative or pending at the time of the encounter, N23 is first-listed.
• When a confirmed stone causes hematuria, code the stone first. Add R31.x only if hematuria carries distinct clinical significance beyond the stone diagnosis.
• Symptoms integral to the stone diagnosis, such as flank pain, nausea, and dysuria, are not separately coded per Section IV.J.

Inpatient Sequencing Rules

In inpatient settings, the principal diagnosis is the condition established after study to be chiefly responsible for the admission. The UHDDS definition governs.

• If admitted for a stone and the stone is confirmed by discharge, the appropriate N20 or N13.2 code is the principal diagnosis.
• If admitted with colic and the stone passes before discharge without confirmation, N23 remains appropriate unless imaging finally confirms a stone location.
• Acute kidney injury (N17.9) caused by stone obstruction is coded additionally when documented and managed separately.

When Stone Codes Are Coded as Additional Diagnoses

A kidney stone code is appropriately added alongside a primary diagnosis in three scenarios:

• The primary encounter is a stone procedure (e.g., ureteroscopy or ESWL). The stone code links to the CPT code as the medical necessity diagnosis.
• The patient has CKD (N18.x) as the primary condition, and a stone episode requires a separate workup and management.
• A stone is found incidentally during imaging ordered for a different condition. The stone is coded additionally if it is documented and managed.

Documentation Requirements for Each Kidney Stone Code

Documentation determines whether a kidney stone claim survives a payer audit. Each code has specific requirements that must be present at the time of claim submission. Documentation cannot be added retroactively after a denial.

N20.0: Calculus of the Kidney

• Imaging report (CT, ultrasound, or KUB X-ray) confirming a stone in the kidney.
• Imaging result referenced in the provider note, not just in the radiology report alone.
• Explicit documentation that hydronephrosis is absent — “no hydronephrosis” or “non-obstructing renal calculus.”
• Stone size and location within the kidney (e.g., lower pole, renal pelvis) for clinical completeness.
• Provider signature with date and time of service.

N20.1: Calculus of the Ureter

• Imaging confirming the stone is located in the ureter, not the kidney.
• Explicit documentation of the absence of hydronephrosis.
• Ureteral location specified (proximal, mid, distal ureter) for operative planning and payer review.
• Any associated symptoms documented by the provider, not only by the patient.

N13.2: Hydronephrosis with Calculous Obstruction

• Imaging confirming both the stone (kidney or ureter) AND hydronephrosis simultaneously.
• Provider note referencing both findings, not just the radiology report.
• Degree of hydronephrosis documented (mild, moderate, severe) when available.
• N20.x must not appear on the same claim for the same encounter (Excludes1).
• If infection accompanies hydronephrosis and obstruction, use N13.6 instead of N13.2.

N23: Unspecified Renal Colic

• Documentation of classic colic symptoms
• Negative or pending imaging at the time of the encounter. Once imaging confirms, update the code.
• Provider assessment explicitly noting renal colic or stone suspicion without confirmed imaging.
• No confirmed stone code (N20.x or N13.2) on the same claim for the same encounter.

Kidney Stones in Nephrology and Urology Patients

Kidney stones in a nephrology practice often co-exist with CKD, glomerular disease, or metabolic disorders. The coding decision tree is more complex than a single isolated stone episode in urology.

Stones in CKD Patients

When an established CKD patient presents with a kidney stone, the sequence is based on the primary reason for the encounter:

• If admitted for the stone: code N20.x or N13.2 first. Add N18.x as an additional diagnosis.
• If the CKD encounter includes incidental stone management: code N18.x first. Add the stone code additionally.
• Acute kidney injury (N17.9) caused by obstruction from the stone is coded additionally when documented.

Metabolic Stone Disease: Adding Cause Codes

When the provider documents the metabolic cause of recurrent stones, add a cause code alongside the stone code:

Metabolic Cause	Code	When to Add
Hypercalciuria / hyperparathyroidism	E21.x	Provider documents hyperparathyroidism as the cause of calcium stones
Hyperuricosuria / gout	M10.x	Provider documents gout-related uric acid stone formation
Cystinuria	E72.01	Provider documents cystine stone composition by stone analysis
Primary hyperoxaluria	E72.53	Provider documents oxalate stones with primary hyperoxaluria
Renal tubular acidosis	N25.89	Provider documents RTA as contributing cause of stone formation

Staghorn Calculi

Staghorn calculi stones that fill the renal pelvis and branch into multiple calyces are coded N20.0 in ICD-10-CM. There is no separate staghorn calculus code. The staghorn character of the stone must be documented in the operative note to support PCNL coding (CPT 50081 for complex PCNL) rather than the simple PCNL code (CPT 50080).

CPT Codes Commonly Paired with Kidney Stone ICD-10 Codes

ICD-10 codes establish medical necessity for every CPT code billed in the same encounter. When a CPT code lacks a matching ICD-10 diagnosis, the claim fails medical necessity review.

The CPT codes below are the primary codes billed for kidney stone diagnosis and treatment. The ICD-10 pairing determines whether the claim clears first-pass review.

CPT Code	Description	ICD-10 Pairing Notes
74178	CT abdomen and pelvis without contrast	N20.x, N13.2, or N23 provide strong medical necessity for stone workup imaging
74177	CT abdomen and pelvis with contrast	Use N20.x or N13.2 when contrast is ordered to evaluate stone-related complications
76770	Ultrasound, retroperitoneal	Pairs with N20.x, N13.2, or N23 for stone detection or hydronephrosis evaluation
50590	ESWL — extracorporeal shock wave lithotripsy	N20.0 for renal stone; N20.1 for ureteral stone. Bill 50590 once per kidney regardless of stone count
52352	Ureteroscopy with stone removal/manipulation (no lithotripsy)	N20.1 (ureteral stone) primary. Do not add 52353 for fragment removal — it is bundled
52353	Ureteroscopy with laser lithotripsy (no stent)	N20.1 or N20.0 depending on stone location. Fragment removal is bundled — do not add 52352
52356	Ureteroscopy with lithotripsy and ureteral stent placement	N20.1 primary. Do not report 52353 or 52332 separately when using 52356
50080	PCNL — simple (stone up to 2 cm, single location, non-branching)	N20.0 primary. Staghorn calculi and complex stones require 50081, not 50080
50081	PCNL — complex (stone >2 cm, branching, multiple locations)	N20.0 primary. Operative note must support complexity to justify 50081 over 50080
52332	Ureteral stent placement (indwelling stent, no lithotripsy)	N20.1 or N13.2 for stent placed to relieve obstruction. Do not bill with 52356
99213–99215	Office E/M — established patient	N20.x, N13.2, or N23 for stone follow-up encounters. Complexity level drives E/M selection

CPT Bundling Rules for Stone Procedures

Bundling violations are the second most common denial category in kidney stone billing after Excludes1 violations. Key rules:

• 52352 cannot be reported alongside 52353 or 52356 for the extraction of fragments from the same lasered stone. Fragment removal is bundled into the lithotripsy code.
• 52356 includes stent placement. Do not separately report 52332 when 52356 is used on the same side in the same session.
• 50590 is reported once per kidney regardless of how many stones are treated. Multiple stones in one kidney do not justify a second 50590.
• For bilateral ESWL, append modifier 50 to 50590. Use LT and RT modifiers to distinguish sides. For staged bilateral sessions, append modifier 58 to the second encounter.

Common Denial Patterns in Kidney Stone Billing

Most kidney stone claim denials fall into one of five categories. Understanding each prevents recurring revenue loss.

Denial Type	Root Cause	Fix
Excludes1 violation	N20.x billed alongside N13.2 when hydronephrosis is documented	Use N13.2 alone when hydronephrosis is present. N20.x is excluded.
No imaging documentation	N20.x coded without CT, ultrasound, or KUB X-ray in the chart	CT, ultrasound, or KUB must confirm stone location before any N20 code is assigned.
Wrong location code	N20.0 used when stone is confirmed in the ureter	Review the radiology report to confirm stone location before coding.
Medical necessity failure	CPT code (e.g., 50590 or 52353) submitted without a linked stone ICD-10 code	Link every procedure CPT code to the appropriate N20 or N13.2 diagnosis code.
CPT bundling violation	52352 billed alongside 52353 for fragments of the same lasered stone	Fragment removal is bundled into 52353 and 52356. Do not separately report 52352.

COMMON DENIAL SCENARIO A urologist performs laser ureteroscopy with lithotripsy (52353) on a ureteral stone. The operative report notes basket extraction of several stone fragments at the end of the case. The coder adds 52352 for the fragment removal. The claim is denied for bundling. The fix: 52353 already includes fragment removal. 52352 is not separately billable for fragments of the same stone that was just lasered.