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N20.0

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N20.0 - Calculus of Kidney

Short Description

N20.0 - Calculus of kidney (renal calculus): use for a kidney stone located in the renal pelvis or calyces without simultaneous ureteral stone.

Full Description & Clinical Context

N20.0 describes urolithiasis confined to the kidney, including stones in the renal pelvis or calyceal system, and is a billable, specific ICD-10-CM diagnosis code.
It is typically assigned when imaging (e.g., CT, KUB, ultrasound) confirms a renal stone without concurrent ureter or bladder calculi.
Clinically, patients often present with flank pain, hematuria, or renal colic, but the diagnosis code is driven by confirmed stone location, not symptoms alone.

Key coding concept:

  • N20.0 = kidney only
  • Use other codes if stone is in ureter (N20.1) or both kidney and ureter (N20.2).

Code Details

  • Code set: ICD-10-CM
  • Full code: N20.0
  • Title: Calculus of kidney (renal calculus).
  • Code type: Billable/specific diagnosis code usable for reimbursement claims.
  • Clinical category: Urolithiasis within the kidney (nephrolithiasis).

When to Use N20.0

Use N20.0 when ALL of the following are true:

  • Imaging or other diagnostic evidence confirms a stone within the kidney (pelvis or calyces).
  • There is no documented ureteral stone (otherwise see N20.1 or N20.2).
  • Documentation supports a current, active condition (not just remote history).

Common documentation phrases that support N20.0:

  • “Nonobstructing right renal calculus”
  • “2 cm stone in left renal pelvis”
  • “Multiple calyceal stones in the right kidney”
  • “Staghorn calculus occupying renal pelvis and calyces” (may still code as N20.0; complexity is reflected in CPT).

When Not to Use N20.0

Consider a different code when:

  • Kidney + ureter stone: Use N20.2 - Calculus of kidney with calculus of ureter.
  • Ureter-only stone: Use N20.1 - Calculus of ureter when location is confined to the ureter.
  • Bladder stone: Use N21.0 - Calculus in bladder.
  • Location not specified: If the site in urinary tract is unclear, use N20.9 - Urinary calculus, unspecified (avoid when more specific information is available).
CodeDescriptionWhen Used
N20.0Calculus of kidneyStone limited to kidney (renal pelvis/calyces)
N20.1Calculus of ureterStone confined to ureter
N20.2Calculus of kidney with calculus of ureterStones in both kidney and ureter
N20.9Urinary calculus, unspecifiedSite not specified in urinary tract
N21.0Calculus in bladderBladder stones
N23Unspecified renal colicSymptoms (renal colic) when stone not confirmed

Combination & Companion Codes

Obstruction & Hydronephrosis

Kidney stones frequently cause obstruction and hydronephrosis; these may be captured with combination or companion codes:

  • N13.2 - Hydronephrosis with renal and ureteral calculous obstruction for obstructive uropathy due to stone causing hydronephrosis.
  • N13.30/N13.39 - Other obstructive uropathy if obstruction is present but not otherwise specified.

Note

Per urology coding guidance, N20.0 and N13.2 may both be reported, but typically N13.2 is sequenced first as the more specific obstructive diagnosis when hydronephrosis due to stone is documented.

Infection & Pyelonephritis

If infection is present:

  • N10 - Acute pyelonephritis for acute infection of the kidney.
  • N13.6 - Pyonephrosis when there is infected hydronephrosis/obstructed kidney with pus.
  • A41.9 - Sepsis, unspecified organism if criteria for sepsis are met.

HCC Information

  • N20.0 itself does NOT map to a CMS-HCC and does not directly affect HCC-based risk adjustment.
  • However, associated conditions such as chronic kidney disease (N18.x) or acute kidney injury (N17.x) may map to HCC categories and should be documented when present.

HCC-related companion examples (if documented):

  • N18.3-N18.5 (CKD stage 3-5) → CKD-related HCC categories.
  • N17.9 (acute kidney failure) when obstruction leads to AKI.

RVU / wRVU Applicability

  • ICD-10-CM diagnosis codes (including N20.0) do not carry RVUs or wRVUs.
  • RVUs are assigned to CPT/HCPCS procedure codes; N20.0 is used to support medical necessity and grouping (e.g., DRG) rather than generating work RVUs directly.

Common CPT Procedure Pairings with N20.0

N20.0 is frequently paired with urology and stone-management CPT codes:

CPTDescription (summary)Typical Scenario with N20.0
50080Percutaneous nephrolithotomy, simple (≤2 cm)Single small renal stone.
50081Percutaneous nephrolithotomy, complex (>2 cm/multiple)Large, branching, or multiple renal stones.
50590ESWL (shock-wave lithotripsy)Non-invasive treatment of renal stone.
52356Ureteroscopy with laser lithotripsy + stentFor ureteral or small intrarenal stones; often with N20.1/N20.2.
52332Cystoscopy with ureteral stent placementDecompression for obstructing stone.
9920xNew patient office/outpatient E/MEvaluation of stone disease in clinic.
9921xEstablished patient office/outpatient E/MFollow-up for renal stone management.

Coding tip: The CPT code reflects the treatment complexity, while N20.0 reflects the anatomic diagnosis (kidney stone).

Sample Coding Scenarios

Scenario 1 - Nonobstructing Renal Stone

Documentation:
“Incidental 5 mm nonobstructing stone in right kidney identified on CT abdomen for abdominal pain. No hydronephrosis.”

Coding:

  • ICD-10-CM: N20.0 (calculus of kidney)
  • CPT (if office visit only): 9921x (based on E/M level).

Notes:

  • No obstruction or infection → no N13.2/N10.

Scenario 2 - Obstructing Stone with Hydronephrosis

Documentation:
“8 mm obstructing stone in left renal pelvis with moderate hydronephrosis and flank pain.”

Coding:

  • ICD-10-CM:
    • N13.2 - Hydronephrosis with renal and ureteral calculous obstruction (principal)
    • N20.0 - Calculus of kidney (additional diagnosis)
    • R10.9 - Unspecified abdominal pain (if provider documents as a diagnosis)
  • CPT (treatment example): 50081-LT for complex PCNL if >2 cm, or 50590 if treated with ESWL.

Scenario 3 - Kidney + Ureter Stone

Documentation:
“2 cm stone in right renal pelvis and 6 mm stone in proximal right ureter; patient with renal colic.”

Coding:

  • ICD-10-CM: N20.2 - Calculus of kidney with calculus of ureter (NOT N20.0 + N20.1).
  • CPT: 50081-RT or 52356-RT depending on procedure performed.

Scenario 4 - Stone with Infection

Documentation:
“Right renal calculus with acute pyelonephritis; positive urine culture for E. coli.”

Coding:

  • ICD-10-CM:
    • N20.0 - Calculus of kidney
    • N10 - Acute pyelonephritis
    • B96.20 - Unspecified E. coli as cause of diseases classified elsewhere (if provider links pathogen).
  • CPT Example: 9922x for inpatient E/M or 50080/50081 if operative treatment is performed.

Documentation Requirements & Best Practices

Key Elements for N20.0

To support N20.0, documentation should ideally include:

  • Anatomic location: “renal pelvis,” “upper pole calyx,” “kidney stone.”
  • Laterality: Right, left, or bilateral (important for CPT modifiers).
  • Stone size: In millimeters or centimeters (supports procedure code selection).
  • Obstruction status: Presence/absence of hydronephrosis or obstruction.
  • Associated infection or renal dysfunction: Pyelonephritis, pyonephrosis, CKD, AKI.

Common Documentation Pitfalls

  • Non-specific site: “Urinary calculus” without clarifying kidney vs ureter vs bladder.
  • Missing obstruction detail when imaging reports hydronephrosis.
  • Omitting CKD/AKI when clearly documented in nephrology or radiology notes.

Coding Tips & Pearls

  • Always code the most specific site: Favor N20.0, N20.1, N20.2 over N20.9 whenever possible.
  • Pair with obstruction/infection codes (N13.2, N10) when clinically documented; N20.0 alone may not fully describe severity.
  • For surgical cases, ensure operative note clearly documents stone size, location(s), and complexity to support proper CPT selection (50080 vs 50081).
  • Do not assume laterality or obstruction from imaging—only code what is explicitly documented by the provider.

Quick Reference Card

ICD-10-CM N20.0 - Calculus of Kidney
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
-  Use for: Stone located in kidney (renal pelvis/calyces).
-  Do NOT use if ureter stone is also present → N20.2.
-  Common companions: N13.2 (obstructive hydronephrosis),
  N10 (acute pyelonephritis), N18.x (CKD), N17.x (AKI).
-  No direct HCC impact, but CKD/AKI do.
-  Typical CPT pairings: 50080/50081 (PCNL), 50590 (ESWL),
  52356 (ureteroscopy), 9920x/9921x (E/M).
-  Documentation: site, laterality, size, obstruction,
  infection, renal function.

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