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

The operative note says “acute on chronic cholecystitis.” Section I.B.8 says to code both and sequence the acute first — so is that K81.0 followed by K81.9?

Short answer

No. K81.2 is a single code for acute cholecystitis with chronic cholecystitis, and where the classification supplies a combination code it is assigned alone. The two-code rule applies where no such code exists.

Scenario

Operative report following laparoscopic cholecystectomy: “Findings consistent with acute on chronic cholecystitis. Calculi present in the gallbladder.”

The coding question:K81.0 with K81.9, or K81.2?

The coding issue

Section I.B.8 and Section I.B.9 are read in the wrong order more often than either is misread on its own. The acute-and-chronic rule tells a coder to report both codes when the Alphabetic Index lists acute and chronic as separate subentries at the same indentation level. It does not survive a combination code: where one code identifies both forms, the Index directs there instead, and the pair is not reported.

Analysis

Check the Alphabetic Index before applying the acute-and-chronic rule. If the subterm structure offers a single entry for the acute-with-chronic form, that code is assigned alone. If the Index instead lists acute and chronic as separate subentries at the same level, both codes are reported with the acute code first. Cholecystitis is the first case: K81.2 covers acute cholecystitis with chronic cholecystitis.

Applied to the scenario:The classification carries a code for the acute-with-chronic form, so Section I.B.9 applies before the acute-and-chronic rule. The documented calculi are a separate fact and are coded from category K80, which describes cholelithiasis with cholecystitis.

What the record must show:Both descriptors have to be applied to the same condition by the provider. A record describing only an acute episode, or only a chronic one, takes the single-form code for what is documented rather than the combination code — K81.0 for the acute form.

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.

A combination code is a single code used to classify: Two diagnoses, or A diagnosis with an associated secondary process (manifestation) A diagnosis with an associated complication Combination codes are identified by referring to subterm entries in the Alphabetic Index and by reading the inclusion and exclusion notes in the Tabular List. Assign only the combination code when that code fully identifies the diagnostic conditions involved or when the Alphabetic Index so directs. Multiple coding should not be used when the classification provides a combination code that clearly identifies all of the elements documented in the diagnosis. When the combination code lacks necessary specificity in describing the manifestation or complication, an additional code should be used as a secondary code.
Guideline · ICD-10-CM Official Guidelines FY2026, I.B.9 Combination Code
If the same condition is described as both acute (subacute) and chronic, and separate subentries exist in the Alphabetic Index at the same indentation level, code both and sequence the acute (subacute) code first.
Guideline · ICD-10-CM Official Guidelines FY2026, I.B.8 Acute and Chronic Conditions
K81.2 Acute cholecystitis with chronic cholecystitis
Title · ICD-10-CM Tabular, K81.2 title · code page

Conclusion

In the scenario:K81.2 for the cholecystitis, with the calculous form coded from category K80 as the documentation supports.

Why:Only the combination code is assigned where it fully identifies the documented conditions, and K81.2 identifies both the acute and the chronic cholecystitis.

Important caveats

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

  • Documented calculi are a separate fact; category K80 classifies cholelithiasis with cholecystitis and carries its own obstruction axis.
  • The acute-and-chronic rule still governs conditions for which the classification supplies no combination code.
  • This answer settles code selection, not which diagnosis is principal for an admission.
  • Common mistake: Applying Section I.B.8 as a standing instruction to report two codes whenever both words appear, without checking whether a combination code exists.
  • 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.B.9
  • ICD-10-CM Official Guidelines FY2026 — I.B.8
  • ICD-10-CM Tabular — K81.2 title

Published September 10, 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.