🧬 ICD-10 CM N21.0 — Calculus in Bladder
Billable Code Confirmed
ICD-10 CM N21.0 is a complete, four-character billable code requiring no further specificity. It sits within category N21 (Calculus of lower urinary tract) and is reportable for reimbursement on any FY2026 claim with a date of service between 10/1/2025 and 9/30/2026.
Non-Billable Parent Codes
N21 (Calculus of lower urinary tract) is a non-billable category header — it must be extended to the fourth character to identify site (bladder, urethra, other, or unspecified) before it can be submitted on a claim.
Clinical Context
ICD-10 CM N21.0 is selected specifically when imaging or cystoscopy confirms the calculus is located within the bladder itself (including a bladder diverticulum), as opposed to the kidney, ureter, or urethra — each of which carries its own distinct code.
Code Classification
This is a diagnosis code describing an anatomic finding (a calculus lodged in the bladder), not a procedure. It is frequently paired with a urologic procedure code documenting removal or fragmentation of the stone.
🔍 Code Description
Bladder calculi (vesical calculi or cystoliths) are mineralized concretions that form or become lodged within the urinary bladder, most often composed of calcium oxalate, struvite, or uric acid crystals. They may arise primarily in the bladder — commonly associated with bladder outlet obstruction, neurogenic bladder, chronic indwelling catheters, or urinary stasis in a N32.4 bladder diverticulum — or migrate down from the upper urinary tract as a N20.1 ureteral stone that passes into the bladder.
Clinically, patients present with suprapubic pain, dysuria, intermittent urinary stream, hematuria, or recurrent urinary tract infection. Diagnosis is confirmed by ultrasound, CT, plain film, or direct cystoscopic visualization. N21.0 is reported once the stone’s location is anatomically confirmed as intravesical, distinguishing it from an upper-tract N20.0 kidney calculus that has not yet migrated.
🌳 Code Tree / Hierarchy
N20-N23 Urolithiasis
│
├── N20 Calculus of kidney and ureter ❌ Non-billable (category)
│ ├── N20.0 Calculus of kidney ✅ Billable
│ └── N20.1 Calculus of ureter ✅ Billable
│
├── N21 Calculus of lower urinary tract ❌ Non-billable
│ │
│ ├── N21.0 Calculus in bladder ◀ THIS CODE ✅ Billable
│ ├── N21.1 Calculus in urethra ✅ Billable
│ ├── N21.8 Other lower urinary tract calculus ✅ Billable
│ └── N21.9 Calculus of lower urinary tract, unspecified ✅ Billable
│
└── N23 Unspecified renal colic ✅ BillableSite Specificity Drives DRG and Procedure Selection
Payers and MS-DRG grouper logic distinguish upper-tract (N20.x) from lower-tract (N21.x) stones because they drive different procedure code sets — cystolitholapaxy for bladder stones versus ureteroscopy or ESWL for kidney/ureteral stones. Defaulting to N21.9 (unspecified) when imaging clearly documents “bladder” risks a specificity denial or query.
Tip
✅ Includes
- Calculus in diverticulum of bladder — a stone forming or lodged within an outpouching of the bladder wall; code the diverticulum itself separately with N32.4 when documented.
- Urinary bladder stone — the general clinical term synonymous with this code; also charted as “vesical calculus” or “cystolith.”
❌ Excludes
Excludes 1
None applicable to N21.0.
Danger
There is no Excludes1 conflict for this code, so there is no common mutual-exclusivity error to flag here — the primary pitfall instead lies in the Excludes2 note below.
Excludes 2
- N20.0 — Staghorn calculus: a branched kidney-pelvis stone. Because staghorn calculi are, by definition, renal (not vesical), both codes may still be reported together if the patient has a separate, distinct staghorn kidney stone in addition to a bladder stone.
📋 Clinical Overview
Bladder Stone vs. Upper-Tract Stone vs. Renal Colic
Correct site assignment changes both the DRG family logic and the expected procedural pathway, so distinguishing where the calculus is lodged at the time of the encounter is the key documentation point.
| Feature | N21.0 | Related N20.0 | Related N23 |
|---|---|---|---|
| Location | Confirmed intravesical (bladder) stone. | Confirmed stone within the kidney/renal pelvis. | Colic symptoms without a confirmed/located stone. |
| Typical driver | Bladder outlet obstruction, neurogenic bladder, chronic catheter, diverticulum. | Metabolic stone disease, dehydration, dietary factors. | Acute flank pain pending imaging confirmation. |
| Typical procedure | Cystolitholapaxy (52317/52318) or cystolithotomy (51050). | ESWL, ureteroscopy, or percutaneous nephrolithotomy. | Supportive care pending workup; may be recoded once located. |
Important
If the documentation only supports “renal colic” or “urinary tract stone, location pending imaging,” do not assign N21.0 — hold for physician query or use the unspecified/renal colic code until anatomic location is confirmed; assigning a wrong site is a common CDI/audit finding.
Manifestations & Symptom Burden
- Suprapubic or pelvic pain — often positional, worsened by movement as the stone shifts against the bladder wall.
- Gross or microscopic hematuria — from mucosal irritation; may prompt a supporting R31.9 code if documented as a distinct concern.
- Dysuria and interrupted urinary stream — the stone can intermittently obstruct the bladder neck or urethral outlet.
- Recurrent urinary tract infection — chronic stasis around the calculus predisposes to infection; code any documented UTI separately.
Tip
💰 HCC Risk Adjustment
ICD-10 CM N21.0 is not HCC-mapped under the current CMS-HCC V28 model and carries no RAF weight of its own. It has no direct risk-adjustment or capture requirement. If the encounter also involves a complication such as acute kidney injury or sepsis secondary to obstruction, code and capture that complication separately, since it may carry independent HCC relevance.
🏥 MS-DRG Assignment
ICD-10 CM N21.0 is a valid principal diagnosis within the MDC 11 – Urinary Stones DRG family:
| DRG | Description |
|---|---|
| 693 | Urinary Stones with MCC |
| 694 | Urinary Stones without MCC |
DRG assignment for the medical Urinary Stones family hinges entirely on whether an MCC (Major Complication or Comorbidity) is documented (e.g., sepsis or acute kidney failure). (Note: CMS previously maintained separate DRGs 691/692 for cases involving ESW Lithotripsy, but these have been deleted; all medical stone cases now group to 693 or 694).
If the stone was instead removed via an operative endoscopic or open procedure (e.g., cystolitholapaxy), the case groups instead to the appropriate MDC 11 surgical (Kidney/Ureter/Bladder procedure) DRG (such as 653-655 or 662-664) rather than the medical “Urinary Stones” family — confirm the PCS code set assigned before finalizing DRG selection.
NCD/LCD note: There is no national coverage determination (NCD) specific to bladder calculus removal. Coverage and medical-necessity documentation requirements for cystolitholapaxy/cystolithotomy are governed at the local level; verify the current Noridian JE/JF LCD and associated billing/coding article for your MAC jurisdiction before claim submission, as coverage articles are updated independently of the ICD-10-CM code set.
🔗 Related ICD-10-CM Codes
Same category (lower urinary tract calculi):
- N21.1 — Calculus in urethra
- N21.8 — Other lower urinary tract calculus
- N21.9 — Calculus of lower urinary tract, unspecified
Related upper-tract and associated conditions:
- N20.0 — Calculus of kidney
- N20.1 — Calculus of ureter
- N20.2 — Calculus of kidney with calculus of ureter
- N13.2 — Hydronephrosis with renal and ureteral calculous obstruction
- N32.4 — Diverticulum of bladder
- N39.0 — Urinary tract infection, site not specified
🛠️ Commonly Associated CPT Codes
- 52310 — Cystourethroscopy with removal of foreign body, calculus, or ureteral stent from urethra or bladder (simple); use for small stones extracted intact without fragmentation.
- 52315 — Cystourethroscopy with removal of foreign body, calculus, or ureteral stent from urethra or bladder (complicated); reflects added difficulty (e.g., sediment irrigation, multiple attempts).
- 52317 — Litholapaxy: crushing or fragmentation of calculus by any means in bladder and removal of fragments; simple or small (less than 2.5 cm).
- 52318 — Litholapaxy: crushing or fragmentation of calculus by any means in bladder and removal of fragments; complicated or large (over 2.5 cm).
- 51050 — Cystolithotomy, vesical calculus, open surgical removal; reserved for large or complex stones not amenable to endoscopic approach.
- 74176 — CT abdomen and pelvis without contrast; frequently the confirmatory imaging study documenting stone location.
🏷️ Modifier Reference
| Modifier | Name | When to Apply |
|---|---|---|
| -59 | Distinct Service | Apply when a bladder stone procedure is performed at a separate session or distinct anatomic site from another same-day urologic procedure that would otherwise be bundled. |
| -51 | Multiple Procedures | Apply when cystolitholapaxy is billed alongside another separately reportable procedure in the same operative session. |
| -52 | Reduced Services | Apply when a planned stone fragmentation/removal is intentionally reduced in scope relative to the full procedure description. |
| -53 | Discontinued | Apply when the procedure is started but terminated early due to patient risk or extenuating circumstances. |
| -58 | Staged | Apply when a planned, related follow-up procedure (e.g., staged fragment removal) is performed during the global period. |
| -78 | Return to OR | Apply when the patient returns to the OR during the global period for a related complication of the original stone procedure. |
| -79 | Unrelated Procedure | Apply when a distinct, unrelated procedure is performed on the same patient during the global period of the original service. |
NCCI Bundling Considerations
Diagnostic cystourethroscopy is bundled into the litholapaxy/removal codes (52310–52318) and should not be billed separately for the same session; append -59 only when a genuinely distinct procedure or site is documented, not merely to unbundle inherently included visualization.
🔬 ICD-10-PCS Crosswalk
- 0TFB3ZZ — Fragmentation in Bladder, Percutaneous Approach; used for percutaneous fragmentation of a bladder calculus in the inpatient PCS code set.
- 0TFBXZZ — Fragmentation in Bladder, External Approach; captures extracorporeal shock wave lithotripsy directed at a bladder stone.
- 0T9B3ZZ — Drainage of Bladder, Percutaneous Approach; relevant when a bladder stone procedure is paired with percutaneous urinary drainage.
💊 Coding Scenarios and Examples
Example 1
Clinical Scenario: A 68-year-old male with benign prostatic hyperplasia and chronic urinary retention presents with suprapubic pain and gross hematuria. Cystoscopy confirms a 1.8 cm bladder calculus. He undergoes cystoscopic litholapaxy with fragmentation and evacuation of the stone.
| Field | Code | Rationale |
|---|---|---|
| CPT | 52317 | Litholapaxy for a calculus under 2.5 cm confirmed by cystoscopy. |
| PDx | N21.0 | Confirmed intravesical calculus location documented on cystoscopy. |
Tip
Sequence N21.0 as principal diagnosis since the stone is the reason for admission and the procedure directed at it. The underlying BPH may be reported as a secondary diagnosis if it is separately evaluated or managed during the stay.
Example 2
Clinical Scenario: A 54-year-old female with a known bladder diverticulum presents with recurrent UTI and imaging showing a calculus lodged within the diverticulum. She undergoes cystoscopic litholapaxy with diverticulum evaluation; a 3.1 cm stone is fragmented and removed.
| Field | Code | Rationale |
|---|---|---|
| CPT | 52318 | Litholapaxy for a calculus 2.5 cm or greater. |
| CPT 2 | 52310 | Not separately reportable here; listed only if a distinct removal step is separately documented — otherwise omit per NCCI bundling. |
| PDx | N21.0 | Calculus in diverticulum of bladder is explicitly included under N21.0. |
Tip
Example 3
Clinical Scenario: A 45-year-old male with a chronic indwelling suprapubic catheter is admitted with fever, dysuria, and imaging confirming a bladder calculus with associated cystitis. He is treated medically for the infection and undergoes open cystolithotomy due to stone size precluding endoscopic removal.
| Field | Code | Rationale |
|---|---|---|
| CPT | 51050 | Open cystolithotomy performed due to stone size/complexity. |
| PDx | N21.0 | Confirmed bladder calculus as the reason for surgical intervention. |
Tip
Report the cystitis as an additional diagnosis if separately documented and evaluated; confirm whether MCC criteria are met (e.g., sepsis) for correct DRG 693 vs. 694 assignment.
⚠️ Coding Pitfalls and Tips
- Pitfall 1: Defaulting to N21.9 (unspecified) when documentation actually specifies “bladder” stone; Tips: Always confirm anatomic site language in the report before falling back to the unspecified code.
- Pitfall 2: Confusing N21.0 with N20.0 (kidney calculus) when a stone has migrated from the upper tract into the bladder; Tips: Code to the location confirmed at the time of the current encounter, not the stone’s site of origin.
- Pitfall 3: Billing diagnostic cystourethroscopy separately alongside 52310–52318; Tips: Diagnostic visualization is bundled into the removal/litholapaxy code per NCCI edits.
- Pitfall 4: Selecting the wrong litholapaxy code (52317 vs. 52318) without documented stone size; Tips: Query the physician for exact stone diameter in centimeters if not stated, since this drives correct code selection.
- Pitfall 5: Failing to separately code an associated bladder diverticulum (N32.4) when clinically significant and separately managed; Tips: Review the full imaging/operative note for diverticulum documentation beyond the stone finding itself.
- Pitfall 6: Grouping a surgically-treated bladder-stone case into the medical “Urinary Stones” DRG family (693–694) instead of the correct surgical MDC 11 procedure DRG; Tips: Confirm which PCS root operation and approach were coded before finalizing DRG selection.
📚 Sources
1. Centers for Medicare & Medicaid Services (CMS) & National Center for Health Statistics. *ICD-10-CM Diagnosis Code N21.0.* FY2026 ICD-10-CM Code Set; effective 10/1/2025.¹ 2. Centers for Medicare & Medicaid Services. *ICD-10-CM/PCS MS-DRG Definitions Manual, MDC 11 — Diseases & Disorders of the Kidney & Urinary Tract, Urinary Stones (DRG 693–694).*² 3. Thrive Medical Billing. *Understanding CPT Code for Cystolitholapaxy.* 2025.³Sources listed above correspond to superscript citations throughout this note. Verify all Medicare payment figures against your current CMS PFS Lookup tool and applicable MAC LCD prior to claim submission. Please use the latest AAPC/AHIMA Coding Books to verify each code within this note.