Question 1

What is the ICD-10 code for CKD 3a?

Accepted Answer

The ICD-10-CM code for CKD 3a (chronic kidney disease, stage 3a) is N18.31. N18.31 is a billable diagnosis code in the FY2026 ICD-10-CM code set used on Medicare Advantage and commercial claims. It maps to CMS-HCC V28 HCC 329 (Chronic Kidney Disease, Moderate (Stage 3, Except 3B)) with source-labeled reference coefficients HCC 329 0.127.  Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

Question 2

What is ICD-10 code N18.31?

Accepted Answer

N18.31 is the ICD-10-CM diagnosis code for Chronic kidney disease, stage 3a. Stage 3a chronic kidney disease where kidney function is moderately decreased with a GFR of 45-59, representing the milder end of stage 3. N18.31 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. N18.31 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Question 3

Is N18.31 an HCC code?

Accepted Answer

Yes. The final FY2026 CMS mapping file maps N18.31 to HCC 329 (Chronic Kidney Disease, Moderate (Stage 3, Except 3B)) under CMS-HCC V28 with source-labeled reference coefficients HCC 329 0.127.  Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

Question 4

Is N18.31 billable?

Accepted Answer

Yes. N18.31 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. N18.31 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Question 5

Which HCC does N18.31 map to under V28?

Accepted Answer

N18.31 maps to CMS-HCC V28 HCC 329 (Chronic Kidney Disease, Moderate (Stage 3, Except 3B)).  The category numbers, labels, and conditions come from the CMS-HCC V28 model file for payment year 2026.

Question 6

What RAF reference is published for N18.31?

Accepted Answer

N18.31 has source-labeled community, non-dual, aged reference coefficients HCC 329 0.127 under CMS-HCC V28 for payment year 2026.  The coefficients come from the CMS V28 relative-factor file. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

Question 7

What is the V28 vs V24 difference for N18.31?

Accepted Answer

For N18.31, the current CMS-HCC V28 result is HCC 329 (Chronic Kidney Disease, Moderate (Stage 3, Except 3B)). Select a historical effective period before comparing a V24 mapping.  Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

Question 8

What documentation supports N18.31?

Accepted Answer

Documentation must support CKD stage 3a with eGFR 45-59 persisting at least 3 months. The provider's assessment must state stage 3a specifically; a bare eGFR lab value without a provider diagnosis is not sufficient. Do not upgrade N18.31 to N18.32 or N18.4 based on a single low eGFR. Stage progression in CKD must be documented by the provider with a restated diagnosis. N18.31 (stage 3a) maps to V28 HCC 329 (Chronic Kidney Disease, Moderate, Stage 3 Except 3B) at RAF 0.127. CKD risk-adjusts starting at stage 3 under V28; stage 3B (HCC 328) carries the same weight as 3a, so watch for the higher-weighted stage-4 (HCC 327) category as eGFR declines. For N18.31, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. See the MEAT criteria checklist at /meat-criteria for what Monitor, Evaluate, Assess, or Treat looks like in a note. One mnemonic element does not establish that a diagnosis is reportable.

Question 9

Can N18.31 be a primary diagnosis?

Accepted Answer

Usually yes, when it is the condition chiefly responsible for the encounter and the note supports it. The exception is in the code-first instruction: when any associated: diabetic chronic kidney disease (E08.22, E09.22, E10.22, E11.22, E13.22); hypertensive chronic kidney disease (I12.-, I13.-) is documented, that condition is sequenced first and N18.31 follows it. For risk adjustment the order does not matter; the V28 category is the same either way.

Question 10

Which codes cannot be reported with N18.31?

Accepted Answer

No Excludes1 note applies to N18.31 or its category in the FY2026 tabular, so there is no code the classification forbids alongside it. The Excludes2 note lists certain conditions originating in the perinatal period (P04-P96); certain infectious and parasitic diseases (A00-B99); complications of pregnancy, childbirth and the puerperium (O00-O9A); congenital malformations, deformations and chromosomal abnormalities (Q00-Q99); and 15 more (see the notes on this page); those are separate conditions that may be reported together with N18.31 when both are documented.

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N18.31 ICD-10-CM Code: Chronic kidney disease, stage 3a

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N18.31

Is N18.31 an HCC code?

HCC Category Mapping

MEAT review for N18.31

Get the V28 mapping + MEAT cheat sheet

What This Code Means

Coding Tips

Clinical Significance

Documentation Requirements

Commonly Confused Codes

Child Codes

Code Hierarchy

N18.31 code history

Also searched as

More on N18.31

Code family

Related condition guides

Referenced in blog posts

Work N18.31 in HCC Buddy