Chapter 14 — Diseases of the Genitourinary System
Chronic kidney disease staging — and the rule that CKD after a kidney transplant is not, by itself, a transplant complication.
Chapter 14 has one guideline: chronic kidney disease. It matters far beyond the genitourinary chapter, because N18 codes are required as secondary codes with hypertensive CKD (I12, I13), with diabetic CKD, and after kidney transplant. The rule coders most often get wrong is that CKD after a transplant is not a transplant complication.
Stages of chronic kidney disease#
| Code | Stage | Severity |
|---|---|---|
N18.1 | Stage 1 | — |
N18.2 | Stage 2 | Mild CKD |
N18.30–N18.32 | Stage 3 | Moderate CKD |
N18.4 | Stage 4 | Severe CKD |
N18.5 | Stage 5 | — |
N18.6 | End stage renal disease (ESRD) | Assigned when the provider has documented end-stage renal disease |
| Both a stage of CKD and ESRD documented | ALWAYS Assign N18.6 only | — |
CKD after a kidney transplant#
The presence of CKD alone does not constitute a transplant complication. Patients who have undergone kidney transplant may still have some form of CKD because the transplant may not fully restore kidney function. Assign the appropriate N18 code for the stage, plus Z94.0 kidney transplant status.
| Situation | Assign |
|---|---|
| CKD after kidney transplant, no complication documented | The appropriate N18 code for the stage and Z94.0 kidney transplant status |
| Transplant complication documented — failure, rejection or other transplant complication | T86.1-, with a secondary code that identifies the complication — see Section I.C.19.g.3.b |
| Conditions that affect the function of the transplanted kidney other than CKD | A code from subcategory T86.1 and a secondary code identifying the complication |
| Documentation unclear as to whether the patient has a complication of the transplant | QUERY Query the provider |
| CKD with other conditions | Where the sequencing comes from |
|---|---|
| Hypertension and CKD | Section I.C.9.a.2 — a code from I12, with N18 as a secondary code for the stage |
| Hypertension, heart disease and CKD | Section I.C.9.a.3 — a code from I13, with I50 for heart failure if present and N18 for the stage |
| Diabetes and CKD | Section I.C.4.a — the diabetes combination code E08–E13 with CKD, plus N18 for the stage, sequenced per the Tabular List |
| General rule | The sequencing of the CKD code in relation to codes for other contributing conditions is based on the conventions in the Tabular List |
Practice questions#
Q1The record documents both stage 4 chronic kidney disease and end-stage renal disease. What is assigned?
- A
N18.4andN18.6 - B
N18.6only - C
N18.4only - D
N18.9
Show answer & rationale
Correct answer: B. N18.6 only
Rationale. Guideline I.C.14.a.1 states that if both a stage of CKD and ESRD are documented, assign code N18.6 only. Code N18.6 is assigned when the provider has documented end-stage renal disease.
Q2A patient who received a kidney transplant three years ago has stage 3a CKD. There is no documentation of transplant failure or rejection. What is assigned?
- A
T86.19andN18.31 - B
N18.31andZ94.0 - C
T86.10alone - D
N18.31alone
Show answer & rationale
Correct answer: B. N18.31 and Z94.0
Rationale. Guideline I.C.14.a.2 states that patients who have undergone kidney transplant may still have some form of CKD because the transplant may not fully restore kidney function, that the presence of CKD alone does not constitute a transplant complication, and that the appropriate N18 code for the patient's stage of CKD and code Z94.0 kidney transplant status should be assigned. Guideline I.C.19.g.3.b repeats that T86.1- should not be assigned for post kidney transplant patients who have CKD unless a transplant complication is documented.
Q3Which N18 code equates to moderate chronic kidney disease?
- A
N18.2 - B
N18.30-N18.32 - C
N18.4 - D
N18.5
Show answer & rationale
Correct answer: B. N18.30-N18.32
Rationale. Guideline I.C.14.a.1 maps severity to stage: stage 2, code N18.2, equates to mild CKD; stage 3, codes N18.30-N18.32, equate to moderate CKD; and stage 4, code N18.4, equates to severe CKD.
Q4A patient has hypertension and stage 3 CKD. The provider has written nothing linking them. What is assigned?
- A
I10andN18.30 - BA code from
I12and a code fromN18for the stage - CA code from
I13andN18.30 - D
N18.30only
Show answer & rationale
Correct answer: B. A code from I12 and a code from N18 for the stage
Rationale. Guideline I.C.9.a.2 directs assignment of codes from category I12 when both hypertension and a condition classifiable to category N18 are present, with the appropriate N18 code as a secondary code to identify the stage. No linking statement is needed, because the classification presumes a causal relationship between hypertension and kidney involvement under Section I.A.15. CKD is not coded as hypertensive only where the provider indicates it is not related.
Q5A post-transplant patient is documented with acute rejection of the transplanted kidney. What is assigned?
- A
Z94.0andN18.9 - B
T86.1-with a secondary code identifying the complication - C
N18.6only - D
Z94.0only
Show answer & rationale
Correct answer: B. T86.1- with a secondary code identifying the complication
Rationale. Guideline I.C.19.g.3.b states that code T86.1- should be assigned for documented complications of a kidney transplant, such as transplant failure or rejection or other transplant complication, and that conditions that affect the function of the transplanted kidney other than CKD should be assigned a code from subcategory T86.1 and a secondary code that identifies the complication. Guideline I.C.14.a.2 directs a query if the documentation is unclear as to whether the patient has a complication of the transplant.
Scenarios#
A patient with type 2 diabetes mellitus and essential hypertension has stage 4 chronic kidney disease. She also has chronic systolic heart failure. The encounter is for management of the kidney disease. Nothing in the record states that any of the conditions are unrelated.
Show coded answer & rationale
| Seq | Code | Description |
|---|---|---|
| 1 | E11.22 | Type 2 diabetes mellitus with diabetic chronic kidney disease |
| 2 | I13.0 | Hypertensive heart and chronic kidney disease with heart failure and stage 1 through stage 4 CKD — verify in the Tabular List |
| 3 | I50.22 | Chronic systolic (congestive) heart failure |
| 4 | N18.4 | Chronic kidney disease, stage 4 (severe) |
Rationale. Three presumptions of causality operate at once under Section I.A.15, because diabetes with CKD and hypertension with heart and kidney involvement are all linked by “with” in the Alphabetic Index. Guideline I.C.9.a.3 requires I13 where hypertension, heart disease and CKD coexist, plus I50 for the type of heart failure and N18 for the stage. Guideline I.C.14.a.3 states that the sequencing of the CKD code relative to other contributing conditions is based on the conventions in the Tabular List, so read the notes at E11.2-, I13 and N18 before fixing the order.
Guideline: Section I.A.15, I.C.4.a, I.C.9.a.3, I.C.14.a
A kidney transplant recipient with stage 2 CKD is admitted with an Escherichia coli urinary tract infection. The infection is documented as involving the native bladder and is not documented as affecting the function of the transplanted kidney.
Show coded answer & rationale
| Seq | Code | Description |
|---|---|---|
| 1 | N39.0 | Urinary tract infection, site not specified — or the specific site documented; principal diagnosis |
| 2 | B96.20 | Unspecified Escherichia coli as the cause of diseases classified elsewhere |
| 3 | N18.2 | Chronic kidney disease, stage 2 (mild) |
| 4 | Z94.0 | Kidney transplant status |
Rationale. Guideline I.C.14.a.2 directs N18.- plus Z94.0 where CKD follows a transplant with no complication documented, and I.C.19.g.3.a states that pre-existing conditions or conditions that develop after the transplant are not coded as complications unless they affect the function of the transplanted organ. The infection here is documented as involving the native bladder and not affecting graft function, so no T86.1- code is assigned. Section I.C.1.b requires the organism code where the infection code does not identify it.
Guideline: Section I.C.14.a.2, I.C.19.g.3, I.C.1.b
A patient on thrice-weekly haemodialysis is admitted for a vascular access revision. The provider documents end-stage renal disease.
Show coded answer & rationale
| Seq | Code | Description |
|---|---|---|
| 1 | Reason for admission | the code for the access complication or condition that occasioned the admission, per the Tabular List |
| 2 | N18.6 | End stage renal disease |
| 3 | Z99.2 | Dependence on renal dialysis |
Rationale. Guideline I.C.14.a.1 assigns N18.6 where the provider has documented end-stage renal disease. Z99.2 is a status code under Section I.C.21.c.3, which covers dependence on enabling machines and devices, and carries the note that categories Z89-Z90 and Z93-Z99 are for use only where there are no complications or malfunctions of the organ or tissue replaced or the equipment on which the patient is dependent — so read the Tabular List notes carefully when the admission is for an access complication.
Guideline: Section I.C.14.a.1, I.C.21.c.3
Primary sources#
- ICD-10-CM Official Guidelines for Coding and Reporting, FY 2027CMS — the source document for every page on this site (effective 1 Oct 2026)
- NCHS ICD-10-CM files — Tabular List, Index, POA exempt listOfficial code files, addenda and the list of codes exempt from POA reporting
- ICD-10 Coordination and Maintenance CommitteeWhere code proposals are debated; agendas, summaries and meeting materials
- CMS ICD-10 homeCode sets, transition guidance and Medicare coding policy
- AHA Coding ClinicOfficial coding advice from the AHA Central Office — subscription required
- HHS OIG Work PlanActive audit topics — useful for prioritising internal coding audits
- MEDESUN Medical Coding AcademyTraining, credential preparation and audit services by the author