Crystal's Coder Hub🧬 ICD-10 CM N18.1 — Chronic Kidney Disease, Stage 1
Billable Code Confirmed
ICD-10-CM N18.1 is a valid, billable 5-character ICD-10-CM code for FY2026. Characters 1-3 (N18) identify the category of chronic kidney disease; the 4th character placeholder is absent at this level; and the 5th character (.1) specifies Stage 1, defined by kidney damage with a normal or elevated GFR of ≥90 mL/min. No additional characters are required — the code is complete as written.
Non-Billable Parent Codes — Never Submit These
- ❌
N18— 3-character header — lacks the required stage specificity; not a valid billable codeAlways submit N18.1 (all 5 characters) when chronic kidney disease, Stage 1 is documented. Verify the underlying cause is coded first per “Code First” instructions at the N18 category heading.
Clinical Context: Code First the Underlying Cause
ICD-10-CM N18.1 must be sequenced as a secondary code whenever CKD is caused by or associated with hypertension (I12.-, I13.-) or diabetes mellitus (E08.22, E09.22, E10.22, E11.22, E13.22). The “Code First” instruction at the N18 category heading is mandatory — sequencing N18.1 before the causative hypertension or DM code is a coding compliance error. Additionally, use Z94.0 for kidney transplant status and E88.A for associated cachexia when applicable per “Use Additional Code” guidance.
Code Classification
ICD-10-CM Diagnosis Code — wRVU, assistant-at-surgery payable, and global period fields are not applicable to ICD-10-CM diagnosis codes. For procedure-level reference, see the CPT Procedural Crosswalk and ICD-10-PCS Crosswalk sections below.
🔍 Code Description
ICD-10-CM N18.1 classifies Chronic kidney disease, Stage 1 — defined as kidney damage with a normal or increased estimated glomerular filtration rate (eGFR) of ≥90 mL/min/1.73 m². Stage 1 CKD is characterized by the presence of kidney damage markers (e.g., proteinuria, microalbuminuria, hematuria, pathologic findings on imaging or biopsy) despite preserved filtration function; it is the GFR plus the damage marker together that define the stage, not the GFR alone.
The underlying pathophysiology typically involves structural or functional injury to the glomeruli, tubules, renal vasculature, or interstitium secondary to conditions such as hypertension, diabetes mellitus, or glomerulonephritis. Because the GFR is preserved at Stage 1, patients are often asymptomatic, making documentation of laboratory-based damage markers (e.g., UACR >30 mg/g) and provider confirmation of CKD the key CDI driver for accurate code assignment at this stage.
🌳 Code Tree / Hierarchy
N17-N19 Acute kidney failure and chronic kidney disease ❌ Non-billable block
│
├── N17 Acute kidney failure ❌ Non-billable category header
├── N18 Chronic kidney disease (CKD) ❌ Non-billable category header
│ │
│ ├── N18.1 Chronic kidney disease, stage 1 ◀ THIS CODE ✅ Billable
│ ├── N18.2 Chronic kidney disease, stage 2 (mild) ✅ Billable
│ ├── N18.30 Chronic kidney disease, stage 3 unspecified ✅ Billable
│ ├── N18.31 Chronic kidney disease, stage 3a ✅ Billable
│ ├── N18.32 Chronic kidney disease, stage 3b ✅ Billable
│ ├── N18.4 Chronic kidney disease, stage 4 (severe) ✅ Billable
│ ├── N18.5 Chronic kidney disease, stage 5 ✅ Billable
│ ├── N18.6 End stage renal disease ✅ Billable
│ └── N18.9 Chronic kidney disease, unspecified ✅ Billable
│
└── N19 Unspecified kidney failure ✅ Billable
Stage Specificity Impacts HCC Capture — Starting at Stage 3
While N18.1 does not carry HCC weight, documenting and coding the stage accurately now establishes the foundation for tracking progression. When CKD advances to Stage 3 (N18.30/N18.31/N18.32 → HCC 329/328), Stage 4 (N18.4 → HCC 327), or Stage 5/ESRD (N18.5/N18.6 → HCC 326), those codes carry RAF coefficients from 0.127 up to 0.815. Accurate early staging documentation is a CDI best practice for longitudinal risk-adjustment continuity.
✅ Includes
The following clinical terms and scenarios map to N18.1 when documented:
- Chronic kidney disease, Stage 1 with eGFR ≥90 mL/min/1.73 m²
- Kidney damage with normal or increased GFR and confirmed damage markers (proteinuria, microalbuminuria)
- Early CKD in the setting of documented hypertension or diabetes — code the causative condition first
- CKD Stage 1 with kidney transplant status (append Z94.0)
- CKD Stage 1 with associated cachexia (append E88.A)
❌ Excludes
Excludes 1 — Cannot Be Coded Simultaneously with N18.1
| Code | Description | Note |
|---|---|---|
| N/A | No Excludes 1 notations at the N18.1 level | See N18 category heading for sequencing instructions |
Excludes 1 Violation Risk
There are no direct Excludes 1 notations at the N18.1 code level. The most common compliance error is sequencing N18.1 before a hypertensive or diabetic combination code — this is not an Excludes 1 issue but a “Code First” sequencing violation. Always verify the category N18 header instructions before submitting any N18.x code.
Excludes 2 — May Be Coded in Addition if Separately Present
| Code | Description | Note |
|---|---|---|
| N/A | No Excludes 2 notations at the N18.1 level | Acute kidney injury (N17.x) may be coded concurrently with CKD per AKI-on-CKD guidelines; these are not mutually exclusive |
📋 Clinical Overview
CKD Stage Comparison — Staging by eGFR and Damage Markers
CKD staging under KDIGO guidelines is based on both eGFR value and the presence of kidney damage markers sustained for >3 months. The table below contextualizes Stage 1 among the full CKD spectrum.
| Feature | N18.1 — Stage 1 | N18.2 — Stage 2 | N18.4 — Stage 4 |
|---|---|---|---|
| eGFR (mL/min/1.73m²) | ≥90 | 60-89 | 15-29 |
| Clinical description | Kidney damage, GFR normal/high | Mild reduction in GFR | Severe reduction |
| HCC Mapping (v28) | ❌ None | ❌ None | ✅ HCC 327 (RAF ~0.514) |
| CC/MCC Status (MS-DRG) | Neither | Neither | CC |
| Symptom burden | Usually asymptomatic | Mild/subclinical | Moderate-severe uremic symptoms |
| Key coding instruction | Code First underlying cause | Code First underlying cause | Code First underlying cause |
CDI Query Trigger — GFR Documented Without Stage
If the provider documents an eGFR value ≥90 with evidence of proteinuria or microalbuminuria but does not explicitly state “CKD, Stage 1,” a CDI query is warranted. Coders may not infer a CKD stage from laboratory values alone — provider confirmation is required. The query should ask the provider to confirm the diagnosis of chronic kidney disease and specify the stage based on the eGFR and clinical findings.
Manifestations & Symptom Burden
CKD Stage 1 is often clinically silent but may present with or be associated with these conditions, all of which should be coded separately when documented:
- Proteinuria / microalbuminuria: Most common damage marker; often the sole finding in Stage 1 CKD
- Hypertension: Both a cause and complication of CKD; use combination codes I12.- or I13.- as principal per guidelines
- diabetic nephropathy: In DM patients, use combination DM codes (E08.22, E09.22,E10.22, E11.22, E13.22) first, then N18.1
- Anemia of chronic kidney disease: Code D63.1 as an additional code when documented — more prevalent in advanced CKD but may appear early
- Hyperlipidemia: Commonly comorbid; code separately (E78.x)
Coding Manifestations
Always code documented manifestations and comorbidities to fully capture patient complexity. Examples include:
- D63.1 — Anemia in chronic kidney disease
- E11.22 — Type 2 diabetes mellitus with diabetic chronic kidney disease, stage 1 (sequence before N18.1)
- I12.9 — Hypertensive chronic kidney disease with stage 1-2 CKD or unspecified CKD (sequence before N18.1)
💰 HCC Risk Adjustment (CMS-HCC v28)
| Field | Detail |
|---|---|
| CMS-HCC Model Version | v28 (2024-2026 Implementation) |
| HCC Assignment | ❌ Not HCC-Mapped |
| HCC Category | N/A |
| RAF Coefficient | N/A — No RAF contribution |
N18.1 does not map to any HCC category under CMS-HCC v28. CKD stages 1 and 2 are excluded from risk-adjustment mapping because the Medicare Advantage model reserves HCC weight for conditions with meaningful impact on expected resource utilization — which begins at Stage 3 (moderate CKD).
Capture Annually — Prepare for Progression
Although N18.1 carries no RAF weight today, annual documentation of CKD stage is essential because CMS-HCC models are hierarchical — a patient who progresses to Stage 3 must have the stage documented and coded in the claim year of progression to receive HCC credit. Gaps in annual staging documentation create audit risk and delay appropriate risk-adjustment capture. Ensure the underlying causative code (hypertensive or diabetic CKD) is also captured annually, as those combination codes may independently contribute to RAF scoring.
🏥 MS-DRG Assignment
MDC 11 — Diseases and Disorders of the Kidney and Urinary Tract
| DRG | Title | Est. Relative Weight* |
|---|---|---|
| DRG 682 | Renal Failure with MCC | ~1.80 - 2.10 |
| DRG 683 | Renal Failure with CC | ~1.00 - 1.20 |
| DRG 684 | Renal Failure without CC/MCC | ~0.60 - 0.75 |
Approximate. Verify against IPPS FY2026 Final Rule tables.
Sequencing and CC/MCC Status
N18.1 is neither a CC nor an MCC under the MS-DRG system, meaning it does not independently elevate DRG weight when sequenced as a secondary diagnosis. It is most commonly coded as a supporting comorbidity documenting the patient’s baseline kidney function context. When the admitting condition is hypertensive or diabetic CKD-related, sequence the combination code (I12.-, I13.-, or E08.22-E13.22) as the principal diagnosis. Progressed CKD stages N18.4 (CC) and N18.5/N18.6 (MCC) do drive DRG movement significantly — documentation that captures the correct stage is paramount for appropriate reimbursement.
🔗 Related ICD-10-CM Codes
CKD Stage Variants — N18 Category
| Code | Description |
|---|---|
| N18.1 | Chronic kidney disease, stage 1 ← This Code |
| N18.2 | Chronic kidney disease, stage 2 (mild) |
| N18.30 | Chronic kidney disease, stage 3 unspecified |
| N18.31 | Chronic kidney disease, stage 3a |
| N18.32 | Chronic kidney disease, stage 3b |
| N18.4 | Chronic kidney disease, stage 4 (severe) |
| N18.5 | Chronic kidney disease, stage 5 |
| N18.6 | End stage renal disease |
| N18.9 | Chronic kidney disease, unspecified |
Causative / Combination Codes — Must Sequence Before N18.1
| Code | Description |
|---|---|
| I12.9 | Hypertensive chronic kidney disease with stage 1-2 CKD or unspecified CKD |
| I13.10 | Hypertensive heart and chronic kidney disease without heart failure, with stage 1-4 or unspecified CKD |
| E11.22 | Type 2 diabetes mellitus with diabetic chronic kidney disease, stage 1 |
| E10.22 | Type 1 diabetes mellitus with diabetic chronic kidney disease, stage 1 |
| E08.22 | Diabetes mellitus due to underlying condition with diabetic CKD, stage 1 |
Related Renal Conditions — Code Separately When Documented
| Code | Description |
|---|---|
| N17.9 | Acute kidney failure, unspecified (AKI on CKD — code both) |
| D63.1 | Anemia in chronic kidney disease |
| Z94.0 | Kidney transplant status |
| Z99.2 | Dependence on renal dialysis (not applicable at Stage 1, but relevant for tracking trajectory) |
🛠️ Commonly Associated CPT Codes (Nephrology / Primary Care)
Outpatient and Profee Setting Context
These CPT codes are commonly associated with the management, monitoring, and workup of CKD Stage 1 in the outpatient nephrology or primary care setting. Most are evaluation, laboratory, or imaging-based rather than procedural. Modifier -26 applies to interpretation-only billing for imaging studies when the facility owns the equipment.
| CPT Code | Description | Profee Coding Notes (Modifier 26) |
|---|---|---|
| 99213 - 99215 | Office/outpatient E/M visit, established patient | Bill based on MDM or time; CKD Stage 1 with comorbidities often supports moderate MDM (99214) |
| 80053 | Comprehensive metabolic panel | Includes BUN, creatinine, eGFR components; bill as panel rather than components to avoid NCCI edits |
| 82570 | Creatinine, urine (spot urine creatinine for UACR calculation) | Often ordered with 82043 (microalbumin, urine) to calculate albumin-to-creatinine ratio |
| 82043 | Microalbumin, urine (quantitative) | Key damage marker test for Stage 1 CKD confirmation; billed separately from comprehensive panel |
| 76770 | Ultrasound, retroperitoneal (e.g., renal ultrasound) | Modifier -26 if provider interprets only; used to evaluate renal size, echogenicity, obstruction |
| 93306 | Echocardiography (TTE with Doppler) | Associated when hypertensive CKD with suspected cardiac involvement |
NCCI Bundling Considerations
- Comprehensive metabolic panel (80053) includes creatinine (82565) as a component — billing both 80053 and 82565 on the same date triggers an NCCI edit; bill the panel only.
- Microalbumin (82043) is NOT included in 80053 and may be billed separately without an NCCI modifier.
- E/M (99213-99215) billed same-day as an in-office laboratory interpretation requires Modifier -25 on the E/M to confirm a separately identifiable service above and beyond the lab result review.
🔬 ICD-10-PCS Crosswalk (Inpatient Procedures)
When N18.1 is an inpatient diagnosis, these PCS codes are relevant for associated inpatient procedures.
| PCS Section | Body System | Root Operation | Clinical Application |
|---|---|---|---|
| 0 (Medical and Surgical) | T (Urinary System) | B (Excision) | Renal biopsy for histological CKD staging confirmation — e.g., 0TB03ZX (Excision of Right Kidney, Percutaneous, Diagnostic) |
| B (Imaging) | T (Urinary System) | 3 (Ultrasonography) | Renal ultrasound to evaluate kidney size and structural damage — e.g., BT453ZZ (Ultrasonography of Bilateral Kidneys) |
| 4 (Measurement and Monitoring) | F (Physiological Systems) | 1 (Monitoring) | Urinary output monitoring during inpatient admission — e.g., 4A1D70Z (Monitoring of Urinary Pressure, Via Natural/Artificial Opening) |
💊 Coding Scenarios and Examples
Scenario 1 — Outpatient / Nephrology: Hypertensive CKD Stage 1, Established Patient Visit
Clinical Vignette: A 58-year-old male with a 10-year history of hypertension presents to nephrology follow-up. Most recent labs show an eGFR of 94 mL/min/1.73m² and a urine albumin-to-creatinine ratio (UACR) of 45 mg/g on two separate occasions over the past 4 months. The nephrologist documents: “Hypertensive chronic kidney disease, Stage 1 — eGFR preserved, persistent microalbuminuria confirming kidney damage. Continue ACEi, recheck UACR in 3 months.” Moderate MDM documented.
CPT (Profee):
- 99214 — Office visit, established patient, moderate MDM (hypertensive CKD Stage 1 management with data review and medication management)
ICD-10-CM Principal/Primary Diagnosis:
- I12.9 — Hypertensive chronic kidney disease with stage 1-2 CKD or unspecified CKD (Code First per category N18 instruction — hypertension is the documented causative condition)
ICD-10-CM Secondary Diagnoses / Additional Codes:
- N18.1 — Chronic kidney disease, stage 1 (required per I12.- “Use Additional Code” instruction to specify the CKD stage)
Scenario 2 — Inpatient: Hypertensive Urgency with Known CKD Stage 1
Clinical Vignette: A 63-year-old female is admitted for hypertensive urgency with a blood pressure of 198/114 mmHg unresponsive to outpatient therapy. Past medical history includes hypertensive CKD Stage 1 (eGFR 91, UACR 52 mg/g confirmed). She is admitted for IV antihypertensive titration and monitoring. CKD Stage 1 is documented as a comorbidity. No acute renal deterioration during admission.
Principal Diagnosis:
- I10 — Essential (primary) hypertension (Reason for admission — hypertensive urgency; I12.9 not appropriate here as the admission is for hypertensive urgency management, not CKD management; query physician if unclear)
Secondary Diagnoses:
- I12.9 — Hypertensive chronic kidney disease with stage 1-2 CKD (comorbidity)
- N18.1 — Chronic kidney disease, stage 1 (required supplementary code per “Use Additional Code” instruction with I12.-)
MS-DRG Assignment: This combination groups to MDC 05 (Diseases and Disorders of the Circulatory System) based on the principal diagnosis of hypertension. N18.1 is neither a CC nor MCC and does not shift the DRG. If an acute kidney injury were superimposed (AKI on CKD), adding N17.9 (MCC) would shift the grouping significantly.
Scenario 3 — CDI Query: eGFR Documented Without CKD Confirmed by Provider
Clinical Vignette: A 67-year-old male with Type 2 diabetes is admitted for diabetic ketoacidosis (DKA). The H&P includes a lab results section noting “eGFR 92 mL/min/1.73m²” and “urine microalbumin 58 mg/g.” No diagnosis of CKD appears anywhere in the chart. The coder notes the eGFR and UACR values but cannot assign a CKD code without a physician diagnosis.
Action / Outcome: The coder cannot code CKD Stage 1 based on laboratory values alone. A CDI query must be generated asking the admitting or attending physician to clarify whether these values represent a confirmed diagnosis of chronic kidney disease and, if so, to document the stage and any causative link to the patient’s diabetes.
Query Response: Provider updates the assessment to confirm: “Type 2 diabetes mellitus with diabetic chronic kidney disease, Stage 1 — eGFR 92, confirmed microalbuminuria on 2 prior outpatient occasions. CKD is attributable to his longstanding poorly controlled T2DM.”
Corrected ICD-10-CM Coding:
- E11.22 — Type 2 diabetes mellitus with diabetic chronic kidney disease, stage 1 (Principal; Code First per category N18 heading)
- N18.1 — Chronic kidney disease, stage 1 (required additional code per E11.22 tabular instruction)
⚠️ Coding Pitfalls and Tips
| Pitfall or Tip | |
|---|---|
| ❌ | Sequencing N18.1 as Principal Without Checking “Code First.” When CKD is caused by hypertension or diabetes, N18.1 must be a secondary code. Submitting N18.1 as the principal diagnosis in the context of documented hypertensive or diabetic CKD is a sequencing compliance violation and can cause claim denial or audit findings. |
| ❌ | Inferring CKD Stage from Lab Values Alone. A single eGFR ≥90 with proteinuria is not sufficient to code N18.1 — the provider must explicitly document a CKD diagnosis and confirm the stage. KDIGO requires both kidney damage markers AND duration >3 months; coders cannot make that determination independently. |
| ❌ | Using N18.9 When Stage Is Documented. If the provider has documented “CKD Stage 1” anywhere in the record, N18.9 (unspecified) is incorrect and constitutes an undercoding error. N18.9 also does not map to any HCC category, creating a missed opportunity for accurate longitudinal risk profiling. |
| ✅ | Always Append N18.1 After the Causative Code. When the chart contains a hypertensive CKD combination code (I12.-, I13.-) or a diabetic CKD combination code (E08.22-E13.22), always add N18.1 as an additional code per the tabular “Use Additional Code” instruction — this is mandatory, not optional. |
| ✅ | Send a CDI Query When Stage Is Absent. If eGFR and albuminuria values are present but the provider has not documented “CKD” or the stage, send a CDI query before abstracting. This protects the facility from undercoding and establishes an accurate longitudinal baseline for risk-adjustment tracking. |
| ✅ | Code AKI and CKD Simultaneously When Both Present. AKI superimposed on CKD (AKI on CKD) allows dual coding of N17.x (AKI) and N18.1 (CKD Stage 1) per ICD-10-CM guidelines. AKI is typically the principal/higher-acuity diagnosis. This combination is a clinically significant distinction that improves DRG accuracy and risk profiling. |