Nephrology covers a wide range of renal conditions. Chronic kidney disease (CKD), acute kidney injury (AKI), end-stage renal disease (ESRD), glomerulonephritis, diabetic nephropathy, and hypertensive kidney disease each present distinct clinical and coding challenges. Each condition maps to a specific ICD-10-CM code, and the wrong code or a missing stage designation on a claim means a denial.
The case for accurate nephrology billing is straightforward. According to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), Medicare spending for CKD beneficiaries aged 66 and older reached nearly $77 billion in 2021. ESRD-related Medicare spending totaled an additional $52.3 billion that same year.
With payer scrutiny at this scale, every nephrology practice submits claims in a high-stakes environment where coding errors carry real revenue consequences. This guide covers the most important nephrology ICD-10-CM codes used in nephrology billing. They are organized by disease category, along with documentation requirements, combination coding rules, and denial prevention guidance.
ICD-10-CM Codes for Chronic Kidney Disease (CKD)
Chronic kidney disease is classified in the ICD-10-CM system under the N18 code category. CKD staging follows the Kidney Disease Improving Global Outcomes (KDIGO) classification, which assigns stages based on glomerular filtration rate (GFR).
CKD Stage Codes (N18 Series)
The following table presents the 2026 ICD-10 codes for CKD stages, their corresponding GFR thresholds, and clinical context:
| ICD-10-CM Code | Description | GFR Range (mL/min/1.73m²) |
|---|---|---|
| N18.1 | CKD, Stage 1 | ≥90 (with kidney damage markers) |
| N18.2 | CKD, Stage 2 | 60–89 |
| N18.30 | CKD, Stage 3a, unspecified | 45–59 |
| N18.31 | CKD, Stage 3a | 45–59 |
| N18.32 | CKD, Stage 3b | 30–44 |
| N18.4 | CKD, Stage 4 | 15–29 |
| N18.5 | CKD, Stage 5 | <15 (pre-dialysis) |
| N18.6 | End-Stage Renal Disease (ESRD) | <15 (on dialysis or transplant) |
| N18.9 | CKD, Unspecified | Stage not documented |
Coding Note: ESRD ICD-10 Code (N18.6) applies when a patient with Stage 5 CKD begins dialysis or receives a kidney transplant. N18.9 carries the risk of payer scrutiny when used in a patient with a documented staging history. Use N18.9 only when staging is genuinely absent from clinical documentation.
Documentation Requirements for CKD Coding
Accurate CKD coding depends on three documented elements:
- The GFR value or estimated GFR (eGFR) from the most recent laboratory result
- The stage designation explicitly noted by the treating nephrologist
- Any comorbid conditions that modify the code selection (diabetes, hypertension, transplant status)
When the physician documents Stage 3 CKD without specifying 3a or 3b, default to N18.30 (Stage 3, unspecified). Do not split-stage based on GFR alone without physician documentation.
ICD-10-CM Codes for Acute Kidney Injury (AKI)
Acute kidney injury is classified under N17 in ICD-10-CM. AKI is defined as a rapid decrease in kidney function within seven days, measured by a rise in serum creatinine or a decrease in urine output. Below are ICD-10 codes for acute kidney injury:
AKI Code Set (N17 Series)
| ICD-10-CM Code | Description |
|---|---|
| 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 |
| N17.9 | Acute kidney failure, unspecified |
All N17.x codes carry Major Complication or Comorbidity (MCC) status in the MS-DRG system. This significantly affects DRG assignment, expected length of stay, and reimbursement. Because of the high-value status of AKI codes, Medicare Recovery Audit Contractors (RACs) and commercial payers closely scrutinize N17.x claims for clinical validation.
AKI-on-CKD Dual Coding
When a patient with existing CKD develops AKI, both conditions are coded. The ICD-10-CM Official Guidelines (Section I.C.14) permit and require dual coding in this scenario:
- N17.x for the AKI (sequenced as the principal diagnosis if it drove the encounter)
- N18.x for the underlying CKD stage
Practical Note: Clinical documentation must clearly distinguish AKI from CKD progression. Without a physician query establishing AKI as a separate acute event, coders default to the CKD stage code only.
ICD-10-CM Codes for End-Stage Renal Disease (ESRD) and Dialysis
ESRD is coded N18.6 in ICD-10-CM. The code applies once a patient with Stage 5 CKD initiates renal replacement therapy, which can be either hemodialysis, peritoneal dialysis, or a kidney transplant.
ESRD and Dialysis Status Codes
| ICD-10-CM Code | Description |
|---|---|
| N18.6 | End-stage renal disease |
| Z99.2 | Dependence on renal dialysis |
| Z94.0 | Kidney transplant status |
Combination Rule: Z99.2 is coded alongside N18.6 when the patient is dialysis-dependent. Z94.0 is coded alongside N18.6 when the patient has received a kidney transplant. Do not code N18.6 alone for dialysis patients without the Z99.2 status code.
ESRD and Payer Requirements
Medicare reimburses ESRD management through Monthly Capitation Payment (MCP) codes for dialysis patients managed by nephrologists. These CPT codes require corresponding ICD-10-CM codes, specifically N18.6 with Z99.2, to establish medical necessity. Missing or mismatched diagnosis codes are the leading cause of ESRD management claim denials.
ICD-10-CM Codes for Hypertensive Kidney Disease
When hypertension contributes to kidney disease, ICD-10-CM requires combination codes from the I12 and I13 series rather than separate coding of hypertension (I10) and CKD (N18.x).
Hypertensive CKD Codes (I12 Series)
| ICD-10-CM Code | Description |
|---|---|
| I12.9 | Hypertensive CKD with Stage 1–4 CKD, or unspecified CKD |
| I12.0 | Hypertensive CKD with Stage 5 CKD or ESRD |
Additional Code Required: An N18.x code must always accompany I12.x to identify the CKD stage. I12.9 alone without a stage-specific N18 code is incomplete.
Hypertensive Heart and Kidney Disease Codes (I13 Series)
When a patient has hypertension, heart disease, and CKD simultaneously, the I13 series applies:
| ICD-10-CM Code | Description |
|---|---|
| I13.0 | Hypertensive heart and CKD with heart failure, Stage 1–4 CKD |
| I13.10 | Hypertensive heart and CKD without heart failure, Stage 1–4 CKD |
| I13.11 | Hypertensive heart and CKD without heart failure, Stage 5 CKD or ESRD |
| I13.2 | Hypertensive heart and CKD with heart failure, Stage 5 CKD or ESRD |
Coding Rule: I13.x always requires an additional N18.x code for CKD stage specificity, plus a heart failure code (from the I50 series) when heart failure is present.
ICD-10-CM Codes for Diabetic Nephropathy
Diabetic nephropathy ICD-10 codes are combination codes that identify both the diabetes type and the related chronic kidney disease (CKD). These codes replace the separate coding of diabetes and CKD in patients with established diabetic kidney disease.
Diabetic CKD Combination Codes
| ICD-10-CM Code | Description |
|---|---|
| E08.22 | Diabetes due to an underlying condition with diabetic CKD |
| E09.22 | Drug or chemical-induced diabetes with diabetic CKD |
| E10.22 | Type 1 diabetes mellitus with diabetic CKD |
| E11.22 | Type 2 diabetes mellitus with diabetic CKD |
| E13.22 | Other specified diabetes with diabetic CKD |
Additional Code Required: Each of the above codes requires an additional N18.x code to specify the CKD stage. E11.22 + N18.3 (Stage 3), for example, captures a Type 2 diabetic patient with moderate CKD.
Key Exclusion: When hypertension is also present alongside diabetes and CKD, coders must decide the primary causal pathway — hypertension (use I12.x or I13.x) versus diabetes (use E11.22). Document review determines which condition the physician identifies as the primary driver of CKD.
ICD-10-CM Codes for Glomerulonephritis and Nephrotic Conditions
Glomerular diseases form a significant portion of nephrology coding. These conditions involve damage to the glomeruli and cover acute, chronic, and hereditary forms.
Acute and Chronic Nephritic Syndromes
| ICD-10-CM Code | Description |
|---|---|
| N00.9 | Acute nephritic syndrome, unspecified morphologic change |
| N01.9 | Rapidly progressive nephritic syndrome, unspecified |
| N03.9 | Chronic nephritic syndrome, unspecified morphologic change |
| N04.9 | Nephrotic syndrome, unspecified morphologic change |
| N05.9 | Unspecified nephritic syndrome, unspecified morphologic change |
Documentation Note: ICD-10-CM requires documentation of the morphologic lesion type for maximum specificity. Fourth and fifth digit codes (e.g., N00.0 through N00.9) identify whether the lesion is focal segmental, membranous, diffuse, or minimal change. When the physician documents a biopsy result, code to the highest level of specificity available.
Specific Glomerular Conditions
| ICD-10-CM Code | Description |
|---|---|
| N02.2 | Recurrent and persistent hematuria — membranous nephropathy |
| N02.8 | Recurrent and persistent hematuria — IgA nephropathy |
| M32.14 | Lupus nephritis (classified under lupus, systemic) |
| N04.1 | Nephrotic syndrome — focal and segmental glomerular lesions |
IgA Nephropathy Note: IgA nephropathy is one of the most common primary glomerular diseases globally. It is coded under N02.8 in the recurrent/persistent hematuria category. Documentation of biopsy-confirmed IgA deposits is required for this code assignment.
ICD-10-CM Codes for Polycystic Kidney Disease
Polycystic kidney disease (PKD) is a hereditary condition causing fluid-filled cysts to develop in both kidneys. PKD codes fall under the Q61 series in ICD-10-CM.
| ICD-10-CM Code | Description |
|---|---|
| Q61.02 | Congenital renal cyst, unspecified — multicystic |
| Q61.2 | Polycystic kidney, adult type (ADPKD) |
| Q61.3 | Polycystic kidney, unspecified |
| Q61.5 | Medullary cystic kidney (nephronophthisis) |
| Q61.9 | Cystic kidney disease, unspecified |
| N28.1 | Cyst of kidney, acquired |
Distinction: Q61.2 applies to autosomal dominant polycystic kidney disease (ADPKD), which is the most common hereditary kidney disease. N28.1 applies to simple acquired kidney cysts without the hereditary polycystic pattern. These two codes are not interchangeable.
ICD-10-CM Codes for Hematuria and Proteinuria
Hematuria and proteinuria are frequently the presenting signs of underlying renal pathology. These symptom codes are used when no established kidney disease diagnosis has been confirmed, or when the symptom drives a separate workup encounter.
Hematuria Codes (R31 Series)
| ICD-10-CM Code | Description |
|---|---|
| R31.0 | Gross hematuria |
| R31.21 | Asymptomatic microscopic hematuria (AMH) |
| R31.29 | Other microscopic hematuria |
| R31.9 | Hematuria, unspecified |
Coding Rule: Hematuria ICD-10 codes are symptom codes. Once the underlying cause (e.g., IgA nephropathy, bladder pathology) is established, the definitive diagnosis code replaces the hematuria code. Using hematuria symptom codes when a confirmed diagnosis exists is a coding error.
Proteinuria Code
These are the Proteinuria ICD-10 Codes, which are frequently used:
| ICD-10-CM Code | Description |
|---|---|
| R80.9 | Proteinuria, unspecified |
| R80.1 | Persistent proteinuria, unspecified |
ICD-10-CM Codes for Kidney Infections and Obstructive Conditions
Nephrology practices also manage renal infections, obstruction-related conditions, and electrolyte disorders. These codes accompany primary renal diagnoses in multi-code claims.
Pyelonephritis and Infectious Nephritis
| ICD-10-CM Code | Description |
|---|---|
| N10 | Acute pyelonephritis |
| N11.0 | Nonobstructive reflux-associated chronic pyelonephritis |
| N11.1 | Chronic obstructive pyelonephritis |
| N11.9 | Chronic tubulo-interstitial nephritis, unspecified |
Note on N10: Acute pyelonephritis often requires an additional code from the B95-B97 series to identify the causative organism (e.g., B96.20 for E. coli, unspecified). Failing to add the organism code leaves the claim incomplete.
Obstructive Nephropathy
| ICD-10-CM Code | Description |
|---|---|
| N13.30 | Hydronephrosis with obstructive uropathy, unspecified |
| N13.5 | Crossing vessel and stricture of ureter |
| N13.9 | Obstructive and reflux uropathy, unspecified |
ICD-10-CM Codes for Electrolyte Disorders in Nephrology
Electrolyte imbalances are a core complication of CKD and ESRD. Coders frequently assign these codes alongside the primary renal diagnosis in inpatient and outpatient nephrology encounters.
| ICD-10-CM Code | Description |
|---|---|
| E87.5 | Hyperkalemia |
| E87.6 | Hypokalemia |
| E87.1 | Hypo-osmolality and hyponatremia |
| E87.0 | Hyperosmolality and hypernatremia |
| E87.2 | Acidosis (metabolic acidosis) |
| E83.51 | Hypocalcemia |
| E83.52 | Hypercalcemia |
| N25.1 | Nephrogenic diabetes insipidus |
| N25.81 | Secondary hyperparathyroidism of renal origin |
Renal Secondary Hyperparathyroidism: N25.81 is a high-value code in nephrology billing. It reflects a well-documented complication of advanced CKD in which impaired kidneys fail to activate Vitamin D, triggering parathyroid overactivity. This code is frequently under-captured in CKD Stage 4 and 5 patients despite being clearly documented in lab results and treatment records.
ICD-10-CM Codes for Kidney Transplant Management
Post-transplant care is a significant component of nephrology practice volume. Kidney transplant ICD-10 provides specific codes for transplant status, complications, and rejection.
| ICD-10-CM Code | Description |
|---|---|
| Z94.0 | Kidney transplant status |
| T86.10 | Kidney transplant rejection, unspecified |
| T86.11 | Kidney transplant failure |
| T86.12 | Kidney transplant infection |
| T86.19 | Other complications of kidney transplant |
| N18.1–N18.5 | CKD in transplant patient (if applicable) |
Critical coding rule: A patient with a functioning kidney transplant may still develop CKD in the transplanted organ. In that case, both Z94.0 and the appropriate N18.x stage code apply. T86.1x codes apply specifically when a transplant complication is the reason for the encounter.
ICD-10-CM Codes for Kidney Stones (Nephrolithiasis)
Kidney stones (medically termed nephrolithiasis or urinary calculi) are among the most frequently billed diagnoses in nephrology and urology. Renal stones are classified under the N20 ICD-10-CM code range for calculi of the kidney and urinary tract. Code selection depends on the confirmed anatomical location of the stone, determined by diagnostic imaging such as CT scan, ultrasound, or KUB X-ray.
Primary Kidney Stone Codes (N20 Series)
| ICD-10-CM Code | Description |
|---|---|
| N20.0 | Calculus of kidney (nephrolithiasis) |
| N20.1 | Calculus of ureter (ureterolithiasis) |
| N20.2 | Calculus of kidney with calculus of ureter |
| N20.9 | Urinary calculus, unspecified |
N20.0 is the primary code for nephrolithiasis. ICD-10-CM does not specify laterality for nephrolithiasis codes, meaning there is no distinction between the left and right kidney in this code set. When stones are confirmed in both the kidney and ureter simultaneously, N20.2 captures both locations in a single code rather than coding N20.0 and N20.1 separately.
N20.9 applies only when imaging confirms a urinary calculus but does not identify the specific location. Using the wrong code or failing to document the stone’s exact location leads to denials, delays, or underpayments. Coders should query the provider for location specificity before defaulting to N20.9.
Kidney Stone with Obstruction and Hydronephrosis
When a kidney stone causes hydronephrosis, the obstructive condition takes coding priority. When hydronephrosis is present due to a stone, N13.2 is used to indicate obstruction. N13.2 carries an Excludes1 note against N20.0, meaning these two codes cannot be used together on the same claim.
| ICD-10-CM Code | Description |
|---|---|
| N13.2 | Hydronephrosis with renal and ureteral calculus obstruction |
| N13.5 | Crossing vessel and stricture of ureter without hydronephrosis |
| N20.0 | Calculus of kidney — use only when hydronephrosis is absent |
Sequencing Rule: When hydronephrosis is present, N13.2 is sequenced as the principal diagnosis. Kidney Stone ICD-10 Code (N20.0) is excluded in this scenario per the ICD-10-CM Type 1 Excludes note. When no hydronephrosis is documented, N20.0 applies as the principal diagnosis.
Kidney Stone with Associated Conditions
Nephrolithiasis frequently presents alongside or triggers other renal conditions. The following codes apply as additional diagnoses when documented:
| ICD-10-CM Code | Description | When to Apply |
|---|---|---|
| N17.9 | Acute kidney failure, unspecified | Stone causing AKI — dual-coded with N20.x |
| R31.0 | Gross hematuria | When hematuria is a documented symptom |
| R10.9 | Unspecified abdominal pain | Use only when flank pain is not coded separately |
| N28.89 | Other specified disorders of kidney | Renal colic without confirmed calculus |
| Z87.442 | Personal history of urinary calculi | Prior kidney stones — applies when no active stone present |
Combination Coding Rules Every Nephrology Coder Must Know
Nephrology ICD-10-CM coding relies heavily on combination codes. Applying these rules correctly prevents the most common claim denials.
Rule 1: Hypertension and CKD Always Use Combination Codes
ICD-10-CM assumes a causal relationship between hypertension and CKD. Coding I10 (hypertension) and N18.x (CKD) separately, without using I12.x, is incorrect under the Official Guidelines.
Rule 2: Diabetes and CKD Use E-Code Combinations with Additional N18.x
Type 2 diabetes with CKD is coded E11.22 plus the appropriate N18.x stage code. Never code E11 (diabetes unspecified complications) and N18.x separately as if they are unrelated.
Rule 3: ESRD Requires Both N18.6 and Z99.2 for Dialysis Patients
N18.6 alone does not fully capture a dialysis-dependent patient’s coding profile. Z99.2 is required to justify ongoing dialysis-related services.
Rule 4: AKI-on-CKD Requires Dual Coding
When a CKD patient develops AKI, the AKI code (N17.x) and the CKD stage code (N18.x) are both reported. The sequencing depends on what drove the encounter.
Rule 5: Hematuria and Proteinuria Are Symptom Codes — Replace When Diagnosis Is Confirmed
Once the nephrology workup confirms an underlying diagnosis (e.g., IgA nephropathy, lupus nephritis), the confirmed diagnosis code replaces the symptom-level code.
Common Nephrology ICD-10 Coding Errors and How to Avoid Them
Nephrology claims face a specific set of recurring coding errors. The table below identifies the most common errors and their corrections:
| Coding Error | Correct Approach |
|---|---|
| Using N18.9 when the CKD stage is documented | Code the documented stage (N18.1–N18.6) |
| Coding I10 + N18.x separately for hypertensive CKD | Use I12.x combination code + N18.x stage |
| Coding N18.6 without Z99.2 for dialysis patients | Add Z99.2 to all dialysis-dependent ESRD claims |
| Missing organism code with N10 (acute pyelonephritis) | Add B95-B97 series code for the causative organism |
| Using hematuria code (R31.x) after diagnosis confirmation | Replace R31.x with the confirmed diagnosis code |
| Failing to add N18.x with diabetic nephropathy (E11.22) | Always pair E11.22 with the appropriate N18.x stage |
| Using N17.9 without clinical validation documentation | Ensure AKI documentation meets KDIGO Stage 1 criteria |
Why Does Nephrology Billing Demand Precise ICD-10 Coding?
Accurate coding is the foundation of successful reimbursement, but many practices struggle to keep up with changing coding guidelines, payer requirements, and documentation standards. This is why many providers partner with nephrology billing services to improve claim accuracy and optimize revenue collection.
Volume and Chronicity
CKD is a progressive, multi-stage condition requiring ongoing monitoring across years. Each encounter generates billable services, including lab reviews, medication management, dialysis oversight, vascular access procedures, and care coordination. Navigating the operational side of these multi-year care plans requires a structured approach; utilizing a comprehensive nephrology billing guide can help your staff properly map each of those services to an ICD-10-CM code that accurately reflects the patient’s current disease stage and comorbid conditions.
Combination Codes and Linkage Rules
Nephrology ICD-10-CM coding frequently requires combination codes. Those are single codes that capture a condition and its causal relationship with another disease. Hypertension with CKD is not coded with two separate codes. A specific I12.x or I13.x combination code applies. Diabetes with CKD requires the E11.22 series with an additional N18.x stage code. Missing these linkages creates claim discrepancies that trigger denials.
Payer Scrutiny of Medical Necessity
Insurers review nephrology claims to confirm that the ICD-10 diagnosis code supports the services billed. Dialysis management claims require codes indicating ESRD or dialysis dependence. Vascular access procedure claims require documentation of the access type and the underlying renal diagnosis. Unspecified codes that are used repeatedly across a patient’s claims history increase audit exposure.
Stage Specificity Requirements
ICD-10-CM requires CKD to be documented and coded by stage (Stage 1 through Stage 5, or ESRD). A claim submitted with N18.9 (CKD, unspecified) when the patient’s records document Stage 3 CKD is a coding error. Payers use stage-specific codes to evaluate reimbursement appropriateness.
Coders must pull the documented glomerular filtration rate (GFR) from the clinical note and match it to the correct stage code. Because a single documentation oversight can trigger a cascading wave of revenue rejections, many practices look to external experts to manage this risk. Reviewing a vetted list of the top nephrology billing companies can help you find a specialized partner equipped to handle these intricate staging and compliance rules natively.
