Acute kidney injury ICD-10 codes: a working guide to N17.9 and the N17 family

Acute kidney injury turns up on a large share of hospital charts. In the United States, about 1% of patients already have AKI when they arrive, another 2% to 5% develop it during the admission, and it appears in up to 67% of intensive care unit stays, according to the StatPearls acute kidney injury review maintained on the National Library of Medicine’s NCBI Bookshelf (last updated November 2023). That volume is why the acute kidney injury ICD-10 code shows up constantly in inpatient and outpatient billing.

The short answer most coders want is N17.9. The longer answer is what separates a clean claim from a denied one, because the word “AKI” in a progress note can map to at least four different codes depending on what else the provider documented. Unspecified codes are acceptable under the official guidelines when the record genuinely lacks detail, but N17.9 is a low-specificity choice, and on the inpatient side the difference between it and a more specific code can shift the DRG assignment and the severity weighting that follows.

What is the ICD-10 code for acute kidney injury?

The ICD-10-CM code for acute kidney injury, unspecified, is N17.9, acute kidney failure, unspecified. It is a billable, specific code that took effect for the current fiscal year on October 1, 2025 and remains valid through September 30, 2026. It sits in Chapter 14 (Diseases of the genitourinary system), in the N17 to N19 block for acute kidney failure and chronic kidney disease.

Two things about N17.9 catch newer coders off guard. First, ICD-10-CM lists acute kidney injury (nontraumatic) as an inclusion term directly under N17.9, so “acute kidney injury” and “acute renal failure” resolve to the same unspecified code when no cause or type is documented. Clinicians treat AKI as the broader modern term, but the classification does not split them. Second, when you submit claims electronically, drop the decimal point and file it as N179. Some clearinghouses strip it for you, but a stray decimal can trigger a rejection for an invalid format.

Acute kidney injury ICD-10: the N17 code family

N17.9 is the fallback, not the whole story. The N17 category holds five billable codes, and moving off N17.9 to a more specific one usually depends on a single documented word: necrosis.

Every one of these five is billable on its own. The category carries a “code also” note for any associated underlying condition, which is the instruction that quietly drives most AKI claims. It tells you to report the cause alongside the kidney code.

When to reach for N17.0 (acute tubular necrosis)

Acute tubular necrosis is the most common cause of intrinsic, hospital-acquired kidney injury, and it has its own code. If the record says ATN, use N17.0, not N17.9. This holds whether the ATN is ischemic (from prolonged low perfusion) or nephrotoxic (from drugs or contrast). ICD-10-CM does not offer separate codes for ischemic ATN, septic ATN, or drug-induced ATN, a point that trips up coders searching for that level of granularity. They all land on N17.0.

Clinically, ATN is diagnosed from the pattern of injury rather than a single test: muddy brown granular casts on urinalysis, a fractional excretion of sodium above 2% in the classic teaching, and a course that does not respond to fluid replacement the way a prerenal state would. Coders do not make that call, but recognizing the language helps confirm that N17.0 is supported rather than assumed.

A frequent snag: the note contains both “AKI” and “ATN.” Do not report both N17.9 and N17.0 for the same episode. N17.0 is the more specific of the two and already describes acute failure with a named mechanism, so it stands alone. When the documentation is genuinely mixed or contradictory, a provider query is the right move rather than a coder’s guess.

Codes that look right but are not N17.9

This is where accuracy is won or lost. Several phrases sound like acute kidney injury but index somewhere other than N17.

Acute renal insufficiency maps to N28.9

“Acute renal insufficiency” is not a synonym for acute kidney failure in the ICD-10-CM index. It routes to N28.9, disorder of kidney and ureter, unspecified, which carries the inclusion terms renal insufficiency (acute), renal disease (acute) NOS, and nephropathy NOS. N28.9 even lists an Excludes1 note pointing chronic renal insufficiency to N18.9. So a chart that says “acute renal insufficiency” and nothing stronger does not support N17.9. If the provider means acute kidney failure, that is a documentation clarification worth pursuing, because the DRG and severity weighting differ.

Azotemia and prerenal azotemia map to R79.89

Azotemia is a laboratory finding (a buildup of nitrogen waste products in the blood), and it indexes to R79.89, other specified abnormal findings of blood chemistry. Prerenal azotemia, absent a documented diagnosis of acute kidney injury, stays with R79.89 as well. The moment the provider commits to “prerenal AKI” or “prerenal acute kidney failure,” you move to N17.9 (with the “code also” cause, such as dehydration or hypovolemia). Coding the diagnosis off a lab value alone is a common overreach.

Postprocedural and post-operative AKI map to N99.0

Kidney failure that develops as a complication of a procedure or surgery has a dedicated complication code: N99.0, postprocedural (acute) (chronic) kidney failure. Its synonyms include acute kidney injury following a procedure. This is a complications-chapter code, so the cause-and-effect language in the note matters. “AKI after surgery” is not automatically a surgical complication; the provider needs to link them.

Kidney failure not stated as acute or chronic maps to N19

When a note documents kidney failure but never commits to acute or chronic, the code is N19, unspecified kidney failure, which carries uremia NOS as an inclusion term. N19 is not a substitute for N17.9. It is the code for genuinely undifferentiated failure, and it usually signals that a query could sharpen the picture. Reserving N17.9 for documentation that actually says acute keeps the two apart.

Traumatic kidney injury maps to S37.0-

The N17 family is nontraumatic by design. Blunt or penetrating renal trauma belongs to the injury chapter under S37.0- (injury of kidney), which requires a seventh character for the encounter type. The inclusion term under N17.9 spells out “nontraumatic” precisely so these two paths stay separate.

Drug-induced AKI and acute interstitial nephritis

Drug and heavy-metal damage to the tubules and interstitium has its own subcategory: N14.- (drug- and heavy-metal-induced tubulo-interstitial and tubular conditions), with billable options such as N14.19 and N14.2. These carry a note to add an adverse-effect code from the T36 to T50 range (with the correct fifth or sixth character) to identify the drug. If a nephrotoxic drug instead produced documented tubular necrosis, N17.0 is the better fit. Contrast-associated kidney injury is a known gray area, with coders debating N99.0 versus N14.1 depending on how the record frames it.

Acute interstitial nephritis of infectious origin falls under N10, acute pyelonephritis, whose inclusion terms cover acute tubulo-interstitial nephritis. Drug-induced interstitial nephritis moves to the N14 codes. Matching the mechanism to the right family keeps these from all defaulting to a generic kidney code.

Coding acute kidney injury on chronic kidney disease

AKI on CKD, sometimes written acute-on-chronic renal failure, is one of the most-asked scenarios in coding forums. There is no single combination code for it. You report both conditions:

• The AKI with the appropriate N17 code
• The CKD with its stage-specific code from N18.1 through N18.6

For example, acute kidney injury superimposed on stage 4 chronic kidney disease is coded N17.9 plus N18.4. Sequencing follows the circumstances of the admission and the principal diagnosis rules, so the code being treated as the reason for the encounter goes first. One detail worth flagging for clinical documentation teams: CKD has stage codes, but AKI does not, which is exactly the confusion the next section addresses.

Why acute kidney injury has no stage codes

Clinicians stage AKI. The classification does not.

The definitions evolved through three consensus systems. The RIFLE criteria came first in 2004, built on a rise in serum creatinine or a period of reduced urine output. The Acute Kidney Injury Network revised them in 2007 (adding an absolute serum creatinine increase above 0.3 mg/dL, shortening the window to 48 hours, and dropping two outcome categories). Kidney Disease: Improving Global Outcomes (KDIGO) then unified the approach in 2012 and defined the stages 1, 2, and 3 that most hospitals use today, based on serum creatinine change and urine output.

Here is the coding consequence. ICD-10-CM has no stage-specific codes for AKI. “Stage 3 acute kidney injury,” “oliguric AKI,” “non-oliguric AKI,” “mild AKI,” and “severe AKI” all resolve to N17.9 (or N17.0 when ATN is documented). The clinical stage does not change the code. It still belongs in the documentation, because it supports medical necessity, severity of illness, and risk adjustment for DRG and HCC purposes, even though the alphabetic index will not reward it with a more granular code.

Documentation that carries the claim

Because the “code also” note drives so much of AKI coding, the linking language in the chart is what makes or breaks specificity. A few pairings that come up constantly:

• AKI due to dehydration: N17.9 with E86.0 (dehydration)
• AKI due to sepsis: the sepsis code (for example A41.9) is often the principal diagnosis when it prompted the admission, followed by N17.-; if severe sepsis is documented with kidney injury as the acute organ dysfunction, add a code from R65.2-
• AKI from obstruction: N17.- with the obstructive uropathy code (N13.-) and the underlying cause, such as benign prostatic hyperplasia, sequenced by the reason for admission

None of these are guesses a coder should make unilaterally. The provider has to state the causal relationship. When the note lists AKI beside a plausible cause without connecting them, that gap is a legitimate query, not an assumption.

Resolved AKI and history of acute kidney injury

ICD-10-CM does not provide a dedicated “personal history of acute kidney injury” code. Under the general coding guidelines, a condition that has resolved and no longer affects the current encounter should not be reported as an active N17 code. If documentation supports a clinically relevant history that influences current care, the broad Z87.898 (personal history of other specified conditions) is the general option, but the guiding principle is to code only what affects the visit in front of you. Carrying a resolved AKI forward as an active diagnosis is a recurring audit finding.

Conclusion

For fast recall: unspecified acute kidney injury and acute renal failure both take N17.9; documented ATN moves to N17.0; acute renal insufficiency alone is N28.9; azotemia is R79.89; a procedural complication is N99.0; renal trauma is S37.0-. Code AKI and CKD separately (N17.- with N18.-), remember that AKI has no stage-specific codes while CKD does, and let the “code also” note pull in the underlying cause. Every one of the five N17 codes is billable for FY2026, so the real work is not finding a code, it is matching the code to what the provider actually wrote.