ICD-10 Code N22: Calculus of urinary tract in diseases

ICD-10 code N22 is the billable ICD-10-CM code for calculus of urinary tract in diseases classified elsewhere. It’s a manifestation code, so it applies when a urinary stone forms as a direct result of another classified disease, such as gout or schistosomiasis. N22 has no subcodes, and it can never be the principal diagnosis.

Therefore, the disease that caused the stone is coded first, and N22 follows it on the claim. In fact, listing N22 first is the error behind most rejected N22 claims. In short, this guide covers the diseases that lead to N22, the sequencing steps, how it differs from N20, and the documentation payers expect.

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Key takeaways

N22 is a manifestation-only code. It identifies urinary stones caused by a separately classified disease, not primary stone disease (N20.x).

The etiology code always comes before N22 on the claim. N22 can’t be the principal diagnosis, and a claim that lists it first is a coding error.

The tabular list names gout and schistosomiasis as its examples of underlying diseases. The physician note must state the causal link explicitly.

Unlike the WHO’s ICD-10, the US ICD-10-CM has no N22.0 or N22.8. N22 is always reported at three characters.

Practice management software like Pabau keeps the causation note on the patient record. Claims go out through Claim.MD, with eligibility checks and status tracking.

ICD-10 code N22: quick-reference summary

Before building a claim with N22, coders need a few basic facts, so the table below lists them. All data reflects the CMS ICD-10-CM official release for fiscal year 2026, effective October 1, 2025.

What N22 covers: clinical definition and scope

N22 applies when a urinary stone is a direct manifestation of an underlying systemic or classified condition. Idiopathic stone disease, with no identified systemic cause, is coded to N20.x instead. In addition, according to the WHO ICD-10 browser, N22 covers stones anywhere along the urinary tract when their formation is linked to a separately coded disease.

Three clinical cases drive most N22 encounters in urology practice, for example:

• Parasitic infiltration: Schistosoma haematobium infection calcifies the bladder and ureteral walls. As a result, the infection creates a stone-forming setting unlike metabolic urolithiasis.
• Metabolic disease: Conditions such as primary hyperparathyroidism cause chronic hypercalciuria. Calcium oxalate or calcium phosphate stones then form secondary to the parathyroid disorder.
• Systemic disorders with urinary manifestation: Gout causes uric acid stones through hyperuricemia, and Crohn’s disease causes oxalate stones through fat malabsorption. Renal tubular acidosis also produces stones downstream of the primary diagnosis.

Overall, the stone results from another disease in all three cases. That is the test for N22: if the physician documents a causal chain from a classified disease to the stone, N22 applies. Otherwise, default to N20.x.

Underlying diseases that map to N22

Each underlying disease needs its own ICD-10-CM etiology code, so sequence it before N22. For example, the tabular list’s “Code first” note at N22 names gout and schistosomiasis. The other conditions below are known clinical causes that also support N22 when the note documents them.

Physician documentation must state the causal relationship clearly. For example, a note that lists schistosomiasis and a bladder stone without linking them does not support N22. Instead, the link has to be written down, not implied.

Does N22 have subcodes?

No. In the US ICD-10-CM, N22 has no subdivisions, so N22 itself is the billable, specific code. Therefore, you report it at the three-character level every time.

However, the confusion comes from the WHO’s international ICD-10, which splits the category into N22.0 (stones in schistosomiasis) and N22.8 (stones in other diseases). Neither subcode exists in ICD-10-CM, so a US claim carrying N22.0 or N22.8 is invalid. You can confirm the current tabular list in the CDC/NCHS ICD-10-CM browser tool.

The detail lives in the etiology code instead. The disease code in position 1 carries the specificity N22 doesn’t, such as the Schistosoma species or the gout site.

Etiology-manifestation sequencing rules for N22

The ICD-10-CM Official Guidelines for Coding and Reporting make the etiology-manifestation convention a hard sequencing rule. The underlying disease always takes the first code position, because it drives the encounter. Thus, N22 is always an additional code.

Follow these four steps for every N22 encounter:

1. First, confirm the underlying classified disease is clearly documented and has a distinct ICD-10-CM code (e.g. B65.0 for schistosomiasis, E21.0 for primary hyperparathyroidism).
2. Second, confirm the causal relationship is stated in the physician note, not merely co-listed. Phrases like “bladder calculus secondary to schistosomiasis” or “calcium stones due to primary hyperparathyroidism” satisfy this requirement.
3. Third, sequence the etiology code first in the claim’s diagnosis code string (position 1).
4. Finally, add N22 as an additional diagnosis code in the next position. Never place N22 in position 1.

The decision path below puts the first three checks in order, so you can see what to do when one of them fails.

Worked example 1 – Schistosomiasis with bladder calculus:

A patient presents with bladder calculus. Pathology confirms Schistosoma haematobium infection. The physician note states “bladder stone secondary to schistosomiasis.” As a result, the correct coding is B65.0 (Schistosomiasis due to Schistosoma haematobium) sequenced first, then N22 as additional diagnosis.

Worked example 2 – Primary hyperparathyroidism with renal calculi:

A patient with known primary hyperparathyroidism presents for ureteroscopy for a calcium stone. The note documents “recurrent calcium oxalate nephrolithiasis secondary to primary hyperparathyroidism.” Therefore, the correct coding is E21.0 sequenced first, then N22 as additional diagnosis.

N20 vs. N22 in ICD-10-CM: how to choose the right code

N20 and N22 describe two different clinical situations. N20 covers primary or idiopathic urinary stones with no underlying systemic cause. In contrast, N22 covers stones that are manifestations of a separately classified disease.

Using N20 when the record supports N22 misstates the patient’s condition and can lead to payer audits. Likewise, using N22 when the record shows only a stone, with no confirmed causal disease, results in denial.

Instructional notes and code pairings for N22

The ICD-10-CM Tabular List carries instructional notes for N22 that control how and when the code may be used. Coders using the AAPC ICD-10-CM lookup will also see these notes alongside the code entry.

• Code first (mandatory instruction): The tabular list carries a “Code first underlying disease” instruction at N22, naming gout (M1A.-, M10.-) and schistosomiasis (B65.0-B65.9) as examples. This is a binding directive. As a result, placing N22 in position 1 is a coding error.
• N23 – Unspecified renal colic: N23 is not excluded from N22. A patient with N22 who also presents with renal colic (N23) may have both codes on the claim, as they describe different clinical findings. However, avoid repeat coding if the colic is just a symptom of the stone being coded.
• No Excludes1 collision with N20: N20 and N22 are not Excludes1 of each other. A patient could have both a primary stone (N20.x) and a disease-related stone (N22). Because this is uncommon, each stone’s cause needs clear documentation.

Documentation requirements to support N22

N22 claims fail most often because the medical record doesn’t say what the code requires. For a manifestation code, then, the note has to support two diagnoses and the link between them. A clean claim needs that documentation trail in place for every code before it leaves the practice.

The physician note must contain all of the following to support N22:

• Confirmed underlying diagnosis: The systemic or classified disease must be documented by name (e.g. “schistosomiasis,” “primary hyperparathyroidism”). In addition, serology, biopsy, or lab values should back it up.
• Clear causal statement: The note must connect the disease to the stone. Co-listing (“the patient has hyperparathyroidism and kidney stones”) doesn’t satisfy this. Instead, the note must state causation, as in “kidney stones secondary to primary hyperparathyroidism.”
• Imaging and lab proof of the stone: CT KUB, ultrasound, or plain film confirming the stone’s presence and location. Also, stone composition analysis, from a passed stone or surgical specimen, backs the causal argument when available.
• Lab evidence of the underlying disease’s metabolic effect: For example, hyperparathyroidism calls for serum calcium, PTH, and 24-hour urinary calcium. For schistosomiasis, egg antigen testing or bladder biopsy. For gout, serum uric acid and urinary uric acid.

Payer requirements and prior authorization

Payers often review N22 claims for medical necessity, because the code signals a chronic underlying disease. Check the patient’s eligibility before a scheduled lithotripsy or ureteroscopy. A real-time eligibility check confirms active coverage before the procedure is performed.

Standard payer expectations for N22 claims include:

• Correct code sequence on the claim form: Etiology code in diagnosis position 1, N22 in position 2 or later. As a result, clearinghouse and payer edits often reject a reversed order.
• Medical necessity documentation on file: The payer’s criteria must be met for the procedure billed, such as ureteroscopy or lithotripsy. Moreover, that necessity must trace back through the underlying disease to the stone.
• Supporting diagnostics in the record: CT KUB or ultrasound confirming the stone. For instance, lab results should show the underlying disease’s activity, such as PTH levels, uric acid, or schistosomiasis serology. Some payers request these on appeal even if not required upfront.
• Prior authorization for procedures: Lithotripsy and ureteroscopy often require prior authorization. The request must reference both the etiology code and N22 to match the claim at adjudication. Otherwise, an authorization filed with only N20.x on an N22 claim results in a mismatch denial.

Common claim denial reasons for N22

N22 generates a clear denial pattern. In fact, practices tracking medical billing denial codes for their urology line will see N22 rejections cluster around five root causes.

Practices with high N22 denial rates should check whether their urology physicians use a note template with a mandatory “etiology of calculus” field. Indeed, a structured template cuts query turnaround time and improves first-pass claim rates.

How Pabau supports clean N22 claims

Many N22 errors start before anyone opens the code set. The causation statement sits in a dictated note, while the codes get keyed into a separate billing tool. The two are rarely checked against each other before the claim goes out.

Practice management software like Pabau keeps the physician note, the diagnosis codes, and the invoice on the same patient record. You can build a urology note template with a required “etiology of calculus” field, so the causal link is written before the encounter closes. Your coder then checks the code order against the note in one place.

Claims go out through Pabau’s claims software for specialty practices, which connects to Claim.MD for US claims. Run a real-time eligibility check before a lithotripsy, then track each claim’s status from the same screen. Fewer N22 claims come back for rework, so your billing team spends its time on new encounters.

Keep N22 claims documented and on track

Pabau keeps the causation note and diagnosis codes on one patient record, then submits and tracks claims through Claim.MD. Your team spends less time reworking rejected N22 claims.

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Conclusion

In short, N22 is a simple code with one strict rule. Specifically, the underlying disease comes first, and the physician has to connect it to the stone in writing. When N22 claims keep coming back, the fix usually sits in the note template rather than the code book.

So start with the template. Add a required causation field to every stone encounter, and query the physician whenever it’s blank. That single change supports the sequencing, the documentation, and the prior authorization match at once.

Book a demo to see how Pabau keeps your urology notes, diagnosis codes, and Claim.MD claims on one record.

Continue your research

Submitting US claims through a clearinghouse? The Claim.MD clearinghouse guide explains how claims are submitted, checked, and tracked through Claim.MD.

Need to see where diagnosis codes sit in an electronic claim? 837 file formatting and submission covers how the claim file carries and orders diagnosis codes.

Seeing repeated N22 rejections? Denial management in healthcare walks through finding the root cause of a denial and appealing it.

Scheduling a lithotripsy or ureteroscopy? Insurance eligibility verification covers the checks to run before the procedure date.

Auditing your urology documentation? Medical billing compliance sets out what the record must support for every code you bill.

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