ICD code N20.0 – Calculus of kidney

Key takeaways

ICD-10 Code N20.0 covers kidney stones confined to the kidney. A stone in the ureter is coded N20.1, and stones in both locations take N20.2.

Staghorn calculi still map to N20.0, because ICD-10-CM has no separate code for branched renal stones.

N20.0 has no laterality sub-codes, so one code covers left, right and bilateral stones, with the side recorded in the clinical note.

Pabau’s claims management software submits N20.0 claims to US payers through the Claim.MD clearinghouse.

ICD-10 Code N20.0: Definition and quick-reference summary

ICD-10 Code N20.0 is a valid, billable ICD-10-CM code with the official descriptor “Calculus of kidney.” It belongs to Chapter XIV: Diseases of the genitourinary system (N00-N99), within the N20-N23 block covering urolithiasis.

The code has been active since ICD-10-CM replaced ICD-9-CM on October 1, 2015, and has not been revised in any subsequent fiscal year update.

According to the CDC/NCHS ICD-10-CM web tool, N20.0 carries no Excludes1 or Excludes2 notes at the code level itself. The exclusions sit at the N20 category level and apply to conditions such as obstructive uropathy with calculus (N13.2).

Coders should check the tabular list at the category and block level, not only at the individual code. Our ICD-10-CM reference for coders lists the chapters and categories around N20.0.

What N20.0 covers: Inclusions and acceptable uses

N20.0 applies to any renal calculus that remains in the renal parenchyma, renal pelvis, or calyces and has not yet entered the ureter. The ICD-10-CM tabular list includes the following under N20.0:

• Kidney stone (the most common lay term mapped to this code)
• Nephrolithiasis (the clinical term for kidney stone disease)
• Renal calculus (formal anatomical terminology)
• Staghorn calculus (a branched stone that casts the shape of the renal pelvis and calyces)
• Renal stone

Stone composition does not change the code, whether the stone is calcium oxalate, uric acid, struvite, or cystine. ICD-10-CM N20.0 carries no sub-codes for stone type.

A struvite staghorn stone filling the entire collecting system is still coded N20.0. Additional codes for infection or obstruction will likely apply alongside it.

N20.0 vs N20.1 vs N20.2: Choosing the code by stone location

The N20 category contains four codes, and the anatomy of stone location determines which one applies. Assigning N20.0 when documentation shows the stone is in the ureter is a common and avoidable denial trigger for nephrolithiasis claims.

As a practical rule, review the imaging report language. “Renal calculus” or “stone in the left kidney” maps to N20.0. “Ureteral calculus” or “stone at the ureterovesical junction” maps to N20.1. When both locations appear in the same encounter note, N20.2 applies.

Per the CMS ICD-10-CM Official Guidelines, code specificity is always preferred over the unspecified option when documentation supports it. The chart below sets the four outcomes side by side.

Coding bilateral kidney stones and laterality

ICD-10-CM N20.0 has no separate sub-codes for left, right, or bilateral kidney stones. This surprises many coders who expect laterality granularity at the 5th or 6th character, as is common in musculoskeletal and injury codes.

The correct approach for bilateral stones is to assign N20.0 once and document laterality clearly in the clinical notes. A single N20.0 code covers all laterality presentations. Payers do not require separate code submissions for each kidney, and submitting N20.0 twice on the same claim is incorrect. A second N20.0 looks like a duplicate charge.

• Left kidney stone only: N20.0 (document “left” in clinical note)
• Right kidney stone only: N20.0 (document “right” in clinical note)
• Bilateral kidney stones: N20.0 once (document “bilateral” in clinical note)
• Stone in kidney and ureter: N20.2 (not N20.0 + N20.1 separately)

How to code a staghorn calculus

A staghorn calculus is a branched stone that fills the renal pelvis and extends into two or more calyceal branches. It still maps to ICD-10 Code N20.0, because ICD-10-CM has no distinct code for staghorn or coral stones.

What changes with staghorn calculi is the complexity of the accompanying codes. Struvite staghorn stones form in the presence of urease-producing bacteria, so a UTI code (N39.0) is frequently appropriate alongside N20.0.

Obstruction from a staghorn stone may warrant hydronephrosis codes from the N13 category. For inpatient admissions, the full code set affects MS-DRG grouping. DRG assignment is determined by the entire claim, including complication and comorbidity codes, not by N20.0 alone.

Common comorbid codes used alongside ICD-10 Code N20.0

Kidney stone encounters rarely present with N20.0 alone. Coders should review documentation for the following frequently co-coded diagnoses:

Per ICD-10-CM Official Guidelines on symptom coding, renal colic (N23) may be coded alongside N20.0 when both are documented. Hematuria is typically an integral symptom of nephrolithiasis. Code it separately only when the provider specifically addresses it as a distinct condition or when it persists after stone passage.

CPT codes paired with N20.0

The procedure codes billed alongside N20.0 depend on how the stone is managed. Conservative management (hydration, analgesics, medical expulsive therapy) generates an E&M code. Interventional management requires one of the following:

When the plan is shock wave lithotripsy, our guide to CPT code 50590 covers how that procedure is billed. Pabau, the practice management platform we build, sends CPT and ICD-10 pairings like these as electronic claims through the Claim.MD clearinghouse.

Claims go out in CMS-1500 or 837P format to thousands of US payers. Eligibility checks through the same connection confirm coverage before the procedure date.

Payer requirements and prior authorization for N20.0 claims

Prior authorization thresholds for nephrolithiasis procedures vary by payer and change annually. The following general framework applies across Medicare, Medicaid, and most commercial plans. Always verify current payer policies before scheduling elective intervention.

• Imaging confirmation: All major payers require imaging to confirm the stone before accepting N20.0. Accepted modalities include CT without contrast (the standard), kidney-ureter-bladder (KUB) X-ray, and renal ultrasound. Document the modality used and the stone size.
• ESWL (CPT 50590): Most commercial payers and Medicare Advantage plans require prior authorization for elective lithotripsy. Submit N20.0 with the imaging report reference in the clinical notes.
• PCNL (CPT 50080-50081): Prior authorization is nearly universal. Payers typically require documentation of stone size (over 2 cm for 50081), failed conservative management, or staghorn morphology.
• Inpatient vs outpatient: CMS medical necessity criteria for inpatient admission with N20.0 require a documented complication, such as obstruction, infection, or AKI. The stone alone does not qualify. Outpatient observation or same-day surgery is typically expected for uncomplicated stones.

Running insurance eligibility verification before the encounter catches a plan that has lapsed or changed its prior authorization rules. Pabau’s claims management software runs those eligibility checks from the patient record, so urology billing teams catch coverage issues before the patient arrives.

Common claim denial reasons for N20.0 and how to prevent them

Nephrolithiasis claims are easy to get wrong, because code selection pivots on a single anatomical fact that a busy imaging report can bury. The table below covers the top denial causes and their solutions.

Structured denial management workflows help urology billing teams track patterns across N20.0 rejections. They show whether the root cause is documentation, prior auth, or code selection. Clean claim submission for nephrolithiasis starts with confirming stone location from imaging before the claim is built.

Documentation requirements for accurate N20.0 coding

The physician note must support the code the coder assigns. For ICD-10 Code N20.0, the documentation checklist covers:

• Stone location: Kidney (parenchyma, pelvis, or calyces), documented explicitly or confirmed by imaging report language
• Stone size: Required by most payers for procedure authorization; also affects CPT selection (50080 vs 50081)
• Laterality: Left, right, or bilateral, recorded in clinical notes even though it does not change the code
• Stone type (if known): Calcium oxalate, uric acid, struvite, or cystine, which supports metabolic workup coding but does not change N20.0
• Associated complications: Obstruction, hematuria, UTI, or AKI, each coded separately when documented
• Imaging modality: CT without contrast, KUB, or ultrasound, recorded in the encounter note

The physician note is the coder’s primary source, not the EHR problem list. A problem list may still show a historical stone that has already passed. The encounter note reflects the clinical status at the time of the visit. Our overview of medical billing fundamentals explains how that note flows into the claim.

ICD-10-CM code validity and annual updates for N20.0

ICD-10-CM Code N20.0 is valid and active for the current fiscal year. The code has remained unchanged since ICD-10-CM was adopted on October 1, 2015. No revision or deletion notice for it appears in any later FY addendum published by CMS and NCHS.

CMS and NCHS publish code updates each October 1. Coders should verify N20.0’s status annually using the AAPC ICD-10-CM lookup or the official CDC tabular tool. For practices that bill across several specialties, a central code review each October lowers the risk of billing a code that the latest update revised.

How Pabau keeps N20.0 claims accurate from imaging to payment

In many urology practices, a kidney stone claim passes through several hands before it reaches a payer. The imaging report sits in one system, the eligibility check in another, and someone rekeys the claim. Each handoff is a chance to code a ureteral stone as renal or to miss an authorization.

In Pabau, the encounter note, the insurance case and the claim sit on the same patient record. The prior authorization code, dates and sessions are tracked on the case, and Pabau flags a case that is missing one. Claims then go to US payers through Claim.MD as CMS-1500 or 837P submissions.

Electronic remittance advice posts back against that same record. A denied N20.0 claim shows up next to the note that explains it. The team can correct the code and resubmit without rebuilding the history.

Code and bill kidney stone claims in one place

Pabau keeps the encounter note, prior authorization and claim on one patient record, then sends claims to US payers through Claim.MD. See how it works for your practice.

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Conclusion

N20.0 itself is rarely the hard part. A kidney stone claim succeeds or fails on the stone’s documented location and on the codes and approvals that travel with it.

The most useful change a urology team can make is to stop coding from the problem list. Code from the imaging report and the encounter note, and confirm prior authorization before an ESWL or PCNL date is set. Those two habits head off the denials this guide describes.

Book a demo to see how Pabau keeps the encounter note, the eligibility check and the claim in one system for your practice.

Continue your research

Need a denial prevention framework for urology billing? Denial codes in medical billing explains common CARC codes and how to build a systematic denial response workflow.

Looking for the full ICD-10-CM submission and claim lifecycle? Understanding the 837 file covers how diagnosis codes like N20.0 travel from EHR to clearinghouse to payer in a standard electronic claim.

Want to understand what ERA remittances reveal about N20.0 rejections? Electronic remittance advice explained walks through 835 ERA data and how to read denial reason codes from payer responses.

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