N17.9: Acute kidney failure, unspecified

The ICD-10-CM code for acute kidney injury when the provider documents the diagnosis without specifying a histological subtype.

Billable

FY2027

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At a glance

Code Family

N17: Acute kidney failure.

HCC Mapping (v28)

None. N17.9 was removed from the CMS-HCC model in v28. It mapped to HCC 135, Acute Renal Failure, under v24.

DRG Grouping

As the principal diagnosis N17.9 groups to MS-DRG 682, 683 or 684, renal failure with MCC, with CC or without CC/MCC, in MDC 11 under the FY2027 MS-DRG v44 grouper. MS-DRG 673, 674 or 675, other kidney and urinary tract procedures, applies where a qualifying O.R. procedure is performed. N17.9 is a complication or comorbidity (CC) under MS-DRG v44 (FY2027), per CMS Table 6J.

Condition

Acute kidney injury

Family Specificity

Five billable child codes structured around the histological subtype of the kidney injury, with N17.9 as the residual code when no subtype is documented.

Billable

Yes

Which N17 code do I assign?

The N17 family splits on the histological subtype of the kidney injury rather than on its severity or its cause. Assign N17.9 when acute kidney injury is documented without a stated subtype.

When documentation says…

Code

Acute tubular necrosis

N17.0

Acute kidney failure with tubular necrosis. The provider must document tubular necrosis, such as acute tubular necrosis. The Index sends Necrosis, tubular to N17.0.

Acute cortical necrosis

N17.1

Acute kidney failure with acute cortical necrosis. The note must name cortical necrosis specifically rather than describing acute kidney injury in general terms.

Medullary necrosis

N17.2

Acute kidney failure with medullary necrosis. The note must name medullary necrosis as the documented pathology.

Other specified acute kidney failure

N17.8

Other acute kidney failure. Assigned when the provider specifies a form of acute kidney failure that none of N17.0, N17.1 or N17.2 describes.

Acute kidney injury, subtype not stated

N17.9

Acute kidney failure, unspecified. The note documents acute kidney injury or acute kidney failure as a confirmed diagnosis with no histological subtype named.

Posttraumatic renal failure

T79.5XXA

Traumatic anuria, initial encounter. The Excludes1 note at category N17 lists posttraumatic renal failure (T79.5). Renal failure attributed directly to trauma takes a T79.5 code, with the seventh character for the encounter, instead of N17.9.

Chronic kidney disease

N18.9

Chronic kidney disease, unspecified. Assigned when the documented process is chronic rather than an abrupt decline in function. Both codes may be reported when acute kidney injury and chronic kidney disease are documented together.

Tabular notes

CODE ALSO

Code also any associated underlying condition. This instruction sits at the N17 parent level and is inherited by N17.9. The underlying cause of the acute kidney injury should be coded when documented. Examples include sepsis, hypovolemia and nephrotoxic medication exposure. Sequencing follows the applicable guidelines.

EXCLUDES1

T79.5: Traumatic anuria, the code for posttraumatic renal failure. This Excludes1 note sits at the N17 category level and is inherited by N17.9. N17.9 and a T79.5 code are not reported together for the same condition. When renal failure is directly caused by trauma and documented as posttraumatic renal failure, assign the T79.5 code for the encounter in place of N17.9.

EXCLUDES2

S37.0: Injury of kidney. This Excludes2 note, traumatic kidney injury (S37.0-), sits at the N17.9 code level rather than at the category level. Both codes may be reported when a traumatic kidney injury and an acute kidney injury meeting N17.9 criteria are documented together. S37.0- represents the structural traumatic injury. T79.5 represents posttraumatic renal failure.

FY2027: EFFECTIVE 1 OCTOBER 2026

N17.9 was valid in the FY2026 code set and is unchanged in the FY2027 update. The FY2027 codes addenda add or delete no code in category N17. The FY2027 tabular addenda change no note at N17.9, at category N17 or in the N17–N19 block.

Operational & financial impact

Why specificity matters beyond the chart: risk adjustment, DRG assignment and denial exposure all follow from which code is selected.

CMS-HCC v28 (PY2024+)

No HCC mapping. N17.9 carries no HCC assignment under CMS-HCC v28.

CMS-HCC v28 is in full effect for payment year 2026.

Documentation of acute kidney injury generates no RAF weight for Medicare Advantage risk scores calculated on v28.

V24 TO V28 TRANSITION

Under CMS-HCC v24, N17.9 mapped to HCC 135, Acute Renal Failure, and contributed to RAF-based risk adjustment.

CMS removed acute kidney injury from the v28 model entirely.

Acute kidney injury documentation that was risk-adjusting under v24 no longer generates RAF weight under v28.

MS-DRG v44 (FY2027)

N17.9 is a complication or comorbidity (CC) under MS-DRG v44 (FY2027), per CMS Table 6J. It is not on the Table 6I MCC list.

N17.0, N17.1 and N17.2, acute kidney failure with tubular, acute cortical or medullary necrosis, are MCCs on the v44 list. Documenting the type of necrosis changes the code and its CC or MCC status.

As a secondary diagnosis, a CC can move an inpatient stay into a higher-weighted DRG tier when N17.9 is documented.

Inpatient capture of N17.9 can affect DRG assignment even though the code carries no HCC weight under v28.

WHERE SPECIFICITY IS LOST

N17.9 is the residual code for acute kidney injury when no histological subtype is documented.

N17.0, N17.1 and N17.2 require the provider to document tubular, cortical or medullary necrosis.

Reporting N17.9 without the underlying condition leaves the Code Also instruction unsatisfied.

Reporting N17.9 when the record documents tubular, cortical or medullary necrosis understates the specificity available in the chart.

Medicare and commercial payers

There is no National Coverage Determination specific to N17.9.

Documentation checklist to support N17.9

Chart elements that support code selection and reduce specificity-driven denials.

Provider documentation of acute kidney injury or acute kidney failure as a confirmed diagnosis.

Supporting laboratory values: elevated serum creatinine, reduced GFR, or reduced urine output consistent with the diagnostic criteria for acute kidney injury.

A clinical acknowledgment by the provider connecting the laboratory findings to the acute kidney injury diagnosis.

The underlying cause when it has been identified, to support the Code Also instruction.

A statement distinguishing the acute process from chronic kidney disease. Both may be coded when both are documented.

The absence of a documented histological subtype. Where tubular, cortical or medullary necrosis is documented, assign N17.0, N17.1 or N17.2 instead.

For inpatient stays, the present on admission indicator for N17.9, reported as present when the acute kidney injury developed before or at admission.

For outpatient encounters, provider documentation of the diagnosis rather than elevated creatinine values alone.

FAQ

Is N17.9 a billable code?

Yes. N17.9 is billable at the fourth-character level. The parent category N17 is not billable and cannot be reported on a claim.

Does N17.9 map to an HCC under CMS-HCC v28?

No. CMS removed acute kidney injury from the v28 model entirely. N17.9 mapped to HCC 135, Acute Renal Failure, under CMS-HCC v24. It carries no HCC assignment under v28, which is in full effect for payment year 2026.

Is acute kidney injury the same as acute kidney failure?

For coding purposes, the two terms are the same. The ICD-10-CM tabular titles category N17 acute kidney failure. It lists acute kidney injury (nontraumatic) as an inclusion term at N17.9. Both terms index to N17.9 when no subtype is named.

What must the record show to support N17.9?

The record needs four elements to support N17.9. Provider documentation of acute kidney injury or acute kidney failure as a confirmed diagnosis. Supporting laboratory values such as elevated serum creatinine, reduced GFR or reduced urine output. A clinical acknowledgment connecting those findings to the diagnosis. The underlying cause when it has been identified. In the outpatient setting, do not code from elevated creatinine values alone without provider documentation of the diagnosis.

When should I use N17.0, N17.1 or N17.2 instead of N17.9?

Use the more specific code whenever the provider documents the histological subtype. N17.0 covers tubular necrosis. N17.1 covers acute cortical necrosis. N17.2 covers medullary necrosis. N17.9 is reserved for acute kidney injury documented with no subtype stated.

Can N17.9 and chronic kidney disease be coded together?

Yes. Neither category N17 nor category N18 carries an Excludes1 note for the other. Both codes are reported when the provider documents both conditions. N17.9 describes an abrupt decline in kidney function. The N18 codes describe a chronic progressive condition.

How is N17.9 sequenced?

Sequence N17.9 as the principal or primary diagnosis when acute kidney injury is the main reason for the encounter. When the acute kidney injury is due to sepsis, sequence the sepsis code from the A40.- or A41.- codes first, with N17.9 as an additional code. When a nephrotoxic drug adverse effect is the cause, sequence the adverse effect code from T36–T50 with the fifth character 5 first, then N17.9.

What changed for N17.9 in FY2027?

N17.9 is unchanged in the FY2027 update, effective 1 October 2026. It was valid in the FY2026 code set. The FY2027 addenda add or delete no code in category N17 and change no note at N17.9. The risk adjustment position is separate. CMS-HCC v28 is in full effect for payment year 2026 and carries no HCC mapping for N17.9.

Related codes

Codes in the same family as N17.9. Only codes with a published page render as links.

Sibling codes in the N17 family

N17.0: Acute kidney failure with tubular necrosis.
N17.1: Acute kidney failure with acute cortical necrosis.
N17.2: Acute kidney failure with medullary necrosis.
N17.8: Other acute kidney failure.

Additional codes to consider

Codes outside the N17 family considered alongside N17.9.

Companion: code alongside when documented

A41.9: Sepsis, unspecified organism, sequenced first when sepsis is the principal diagnosis.
R65.20: Severe sepsis without septic shock, assigned after the sepsis code when the acute kidney injury is associated with the sepsis.
S37.0-: Injury of kidney, permitted alongside N17.9 by the Excludes2 note at the code level.
T36–T50: Adverse effect of drugs, with a 5th or 6th character 5, sequenced after N17.9 when a nephrotoxic drug is the documented cause (Guideline I.C.19.e.5.a).

Consider instead

T79.5XXA: Traumatic anuria, initial encounter, for renal failure attributed directly to trauma.
N18.9: Chronic kidney disease, unspecified, where the documented process is chronic rather than an abrupt decline.
N18.6: End stage renal disease.

Sources

All claims on this page derive from government and professional-standards sources.

National Center for Health Statistics. (2026). International classification of diseases, tenth revision, clinical modification (ICD-10-CM) FY2027 files. https://www.cdc.gov/nchs/icd/icd-10-cm/files.html
Centers for Medicare & Medicaid Services and National Center for Health Statistics. (2026). ICD-10-CM official guidelines for coding and reporting FY2027. https://ftp.cdc.gov/pub/Health_Statistics/NCHS/Publications/ICD10CM/2027/ICD-10-CM-October-1-2026-FY27-Guidelines.pdf
Centers for Medicare & Medicaid Services. (2025). 2026 model software/ICD-10 mappings. https://www.cms.gov/medicare/payment/medicare-advantage-rates-statistics/risk-adjustment/2026-model-software-icd-10-mappings
Centers for Medicare & Medicaid Services. (2026). MS-DRG classifications and software, version 44. https://www.cms.gov/medicare/payment/prospective-payment-systems/acute-inpatient-pps/ms-drg-classifications-and-software