CPT (Current Procedural Terminology) codes are five-digit numeric codes used to describe medical, surgical, and diagnostic services. They are maintained by the American Medical Association and used by healthcare providers, insurers, and Medicare for billing and reimbursement.

What is the difference between facility and non-facility rates?

Non-facility (office) rates are what Medicare pays when a service is performed in a physician's office. Facility rates are lower because when a service is performed in a hospital or ambulatory surgery center, the facility bills separately for overhead costs like equipment and supplies.

RVU stands for Relative Value Unit. Medicare uses RVUs to measure the value of physician services based on three components: physician work, practice expense, and malpractice cost. Total RVUs are multiplied by the conversion factor ($33.40 in 2026) to calculate the Medicare payment amount.

Is N18.31 a billable ICD-10-CM code?

Yes. N18.31 (Chronic kidney disease, stage 3a) is a billable/specific ICD-10-CM code and can be reported on a claim when the documentation supports it.

What HCC does N18.31 map to?

N18.31 maps to HCC329 (Chronic Kidney Disease, Moderate (Stage 3, Except 3B)) in the CMS-HCC V28 risk-adjustment model (Medicare Advantage / Part C) for payment year 2026. Risk-adjustable diagnoses must be documented and resubmitted each year — and survive the CMS-HCC hierarchy and edits — to count toward a member's risk score.

ICD-10-CM · N00–N99BillableHCC329

ICD-10-CM Code N18.31

Chronic kidney disease, stage 3a

Source: CMS ICD-10-CM FY2026Effective October 1, 2025Reviewed by the D3rx Clinical Billing Team

Diagnosis information

Billable

Yes

Valid for claim submission

Chapter

N00–N99

Diseases of the genitourinary system

Risk adjustment

HCC

HCC329

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HCC risk adjustment (CMS-HCC V28)

HCC329Chronic Kidney Disease, Moderate (Stage 3, Except 3B)

Model CMS-HCC V28Payment year 2026

In CMS's Hierarchical Condition Category (HCC) model — the risk-adjustment model for Medicare Advantage (Part C) — a documented and submitted N18.31 may contribute to a member's risk score (subject to the CMS-HCC hierarchy and edits), which helps drive the plan's capitated payment for that patient. To count, the diagnosis must be supported to the MEAT standard (Monitored, Evaluated, Assessed, Treated) and reported on an eligible face-to-face encounter at least once each calendar year — risk scores reset annually.

More codes in the N18 category

Other billable ICD-10-CM codes in the same category as N18.31. Coding to the highest specificity the documentation supports is what keeps a claim clean — pick the child code that most precisely matches the diagnosis.

N18.1Chronic kidney disease, stage 1
N18.2Chronic kidney disease, stage 2 (mild)
N18.30Chronic kidney disease, stage 3 unspecified
N18.32Chronic kidney disease, stage 3b
N18.4Chronic kidney disease, stage 4 (severe)
N18.5Chronic kidney disease, stage 5
N18.6End stage renal disease
N18.9Chronic kidney disease, unspecified

Documentation & coding notes

N18.31 is a billable/specific ICD-10-CM code — it can be reported as a primary or secondary diagnosis when the documentation supports it. Code to the highest level of specificity the record allows.
N18.31 is risk-adjustable: it maps to HCC329 in the CMS-HCC V28 model (payment year 2026), the risk-adjustment model for Medicare Advantage (Part C). For the diagnosis to contribute to a member's risk score it must survive the CMS-HCC hierarchy and edits, be documented to the MEAT standard (Monitored, Evaluated, Assessed, Treated), and be submitted on an eligible face-to-face encounter at least once per calendar year.
Always verify the code against the current ICD-10-CM Official Guidelines and the payer's coverage policy before submitting — coverage, medical necessity edits, and sequencing rules vary by payer.

Related N00–N99 codes

N39.0 N18.6 N18.30 N40.0 N17.9

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Medical coding disclaimer

ICD-10-CM codes and descriptions shown are from the CMS FY2026 official code set and HCC mappings from the CMS-HCC V28 model (payment year 2026), shown for educational reference. Official Guidelines, payer coverage, medical-necessity edits, and sequencing rules vary. Always verify with the current ICD-10-CM Official Guidelines and the payer before submitting claims. D3rx is not responsible for coding or billing outcomes.