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Real-world coding question · ICD-10-CM · FY2026 · Intermediate

A chart lists hypertension and CKD stage 4, and nothing in it says whether the two are related. Is this I10 with N18.4, or a code from category I12?

Short answer

Assign I12.9 for the hypertensive chronic kidney disease, then N18.4 for the documented stage. The classification treats hypertension and chronic kidney disease as related unless the provider states they are not.

Scenario

Office note, established patient: “Hypertension, controlled on lisinopril. CKD stage 4, stable, followed by nephrology.” Nothing in the note relates the two conditions or separates them.

The coding question:I10 with N18.4, or I12.9 with N18.4?

The coding issue

ICD-10-CM usually waits for the provider to link two conditions. Hypertension with chronic kidney disease is one of the places where it does the opposite: the link is assumed, and the record has to contradict it. A coder applying the ordinary rule reaches I10 plus a separate stage code and loses the hypertensive kidney disease entirely, which is a different clinical picture and a different code.

Analysis

Two facts decide it. First, are both a hypertension diagnosis and a condition classifiable to category N18 documented? If so, the code comes from category I12 rather than I10 — I12.9 for stage 1 through 4 or unspecified, I12.0 for stage 5 or end-stage renal disease. Second, does the provider state the chronic kidney disease is not related to the hypertension? Only that statement returns the pair to I10 with a separate N18 code. The N18 code is still reported either way, because the I12 code carries a Use Additional Code instruction for the stage.

Applied to the scenario:Both a hypertension diagnosis and a condition in category N18 are documented, which is the whole condition Section I.C.9.a.2 sets for category I12. Stage 4 is below stage 5, so the choice within I12 is I12.9. The stage still has to be reported, and I12.9 carries a Use Additional Code instruction that asks for it.

What the record must show:The record has to carry the hypertension diagnosis, a chronic kidney disease diagnosis, and the stage — I12.9 and I12.0 split on the stage, so an unstaged record forces the less specific choice. A statement that the two conditions are unrelated is the one entry that changes the code.

Applicable official guidance

The official text the answer rests on, quoted as published in the release in effect. A citation with no quotation is one the registry does not carry as text; it is listed under the source references.

Assign codes from category I12, Hypertensive chronic kidney disease, when both hypertension and a condition classifiable to category N18, Chronic kidney disease (CKD), are present. CKD should not be coded as hypertensive if the provider indicates the CKD is not related to the hypertension. The appropriate code from category N18 should be used as a secondary code with a code from category I12 to identify the stage of chronic kidney disease. See Section I.C.14. Chronic kidney disease. If a patient has hypertensive chronic kidney disease and acute renal failure, the acute renal failure should also be coded. Sequence according to the circumstances of the admission/encounter.
Guideline · ICD-10-CM Official Guidelines FY2026, I.C.9.a.2 Hypertensive Chronic Kidney Disease
  • code to identify the stage of chronic kidney disease (N18.1-N18.4, N18.9)
  • code to identify:
  • exposure to environmental tobacco smoke (Z77.22)
  • history of tobacco dependence (Z87.891)
  • occupational exposure to environmental tobacco smoke (Z57.31)
  • tobacco dependence (F17.-)
  • tobacco use (Z72.0)
Use Additional Code · ICD-10-CM Tabular, I12.9 Use Additional Code note · code page
N18.4 Chronic kidney disease, stage 4 (severe)
Title · ICD-10-CM Tabular, N18.4 title · code page

Conclusion

In the scenario:I12.9, then N18.4.

Why:The presumed relationship holds because the note contains no statement that the chronic kidney disease is unrelated to the hypertension, and the stage code follows the I12 code rather than replacing it.

Why coders disagree

The two readings differ over who has to say the conditions are related. For most ICD-10-CM relationships the provider does; for hypertension with chronic kidney disease the classification itself does, and the record has to say the opposite to break it.

What settles it:A provider statement that the chronic kidney disease is not related to the hypertension. Its absence is what leaves the presumed relationship standing.

  • I10 with N18.4, on the reading that a causal link has to be stated before it can be coded.
  • I12.9 with N18.4, on the reading that the classification supplies the link unless the provider rules it out.

Important caveats

What this answer does not decide, and what would change it.

  • A provider statement that the chronic kidney disease is not related to the hypertension breaks the presumption; the pair is then I10 with the N18 stage code.
  • With heart disease or heart failure also documented, the code moves to category I13, which replaces both I11 and I12.
  • Acute kidney injury documented alongside hypertensive chronic kidney disease is reported in addition, sequenced by the circumstances of the encounter.
  • Secondary hypertension is a different classification question and is outside what category I12 covers.
  • Common mistake: Reporting I10 with an N18 code because no sentence in the chart connects the hypertension to the kidney disease. The connection is supplied by Section I.C.9.a.2, and its absence from the note is not a reason to drop it.
  • This answer applies the ICD-10-CM rules of FY2026. Codes and instructions change with each release; the release in effect on the date of service governs.
  • It explains the decision rule and the documentation element that settles it; it does not assign codes to any particular patient record.
  • Payer-specific policies, coverage rules and claim edits are outside its scope.
  • Where the record is ambiguous or contradicts itself, the provider is queried; a diagnosis is not inferred from findings (ICD-10-CM Official Guidelines, Section I.A.19).

Compare these pairs

Each pair below is one the tabular notes link; its Compare page quotes the note and says whether the two can be reported together.

Run this pair through Claim Check

Claim Check reads the codes against the registry notes, the conventions and the Medicare Code Editor edits, and reports what a pair breaks.

Source references

  • ICD-10-CM Official Guidelines FY2026 — I.C.9.a.2
  • ICD-10-CM Tabular — I12.9 Use Additional Code note
  • ICD-10-CM Tabular — N18.4 title

Published September 8, 2026. Independently researched by MedCoder from official CMS/CDC sources. Coding-community discussions identified the question only; no community text is reproduced and no answer is drawn from it.