Combination Codes: One Code for Two Conditions, and When a Second Code Is Still Needed

Official source

“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.”

• Two diagnoses.K80.00, Calculus of gallbladder with acute cholecystitis without obstruction — gallstones and cholecystitis in one code. Category K81 carries an Excludes1 for “cholecystitis with cholelithiasis (K80.-)” precisely so the two are not coded separately. K81.2, Acute cholecystitis with chronic cholecystitis, is the same device for the acute-with-chronic pair.
• Diagnosis with manifestation.E11.22, Type 2 diabetes mellitus with diabetic chronic kidney disease — the “with” convention the linked guide covers. It is also the standard example of the last sentence of the rule: E11.22 carries a Use Additional Code note “to identify stage of chronic kidney disease (N18.1-N18.6),” because the combination code says CKD but not which stage. The secondary code supplies the specificity the combination lacks.
• Diagnosis with complication. The combination categories throughout Chapter 4 and elsewhere that pair a disease with its complication follow the same rule: one code when it names everything documented, plus a secondary code only for detail the combination cannot carry.

1. Look for a combination code through the Index subterms and the Tabular’s inclusion and exclusion notes.
2. If it fully identifies the documented elements, or the Index directs to it, assign it alone.
3. If it lacks specificity for the manifestation or complication, add a secondary code — following any Use Additional Code note.
4. If no combination code exists, code each condition, ordered by any Code First / Use Additional Code notes.
5. Do not assign a combination code when only one of its elements is documented.

1. Gallstones with acute cholecystitis, no obstruction. K80.00 alone.
2. Type 2 diabetes with CKD stage 3b. E11.22 then N18.32 — the combination code needs the stage.
3. Type 2 diabetes; CKD documented as due to another cause. Not E11.22 — the combination code asserts a link the record denies.

• Coding the parts separately when a combination code exists.
• Omitting the secondary code a combination code’s note asks for.
• Assigning a combination code on one documented element.

• Both elements the combination code asserts, or the Index route that presumes them.
• The detail the combination code cannot carry (stage, site, level).