R40.0 — Somnolence
R40.0 is a billable, specific ICD-10-CM code for somnolence. It is valid for submission on a claim.
Excludes1 — never code together
These conditions cannot occur together. Billing both on the same encounter is a denial.
- coma (R40.2-)
Inclusion terms
Alternative wordings a physician may use in the chart for this same code.
- Drowsiness
Excludes1 inherited from the categories above R40.0
These are not written on R40.0, but they bind it: a note on a category applies to every code beneath it. Billing R40.0 with anything listed here is a denial.
Other codes that can never be billed with R40.0
These codes carry an Excludes1 note pointing at R40.0. The conflict binds both ways, but ICD-10-CM only writes it down on one side — so you would not find this by reading R40.0 alone.
- R41.82Altered mental status, unspecified
Risk adjustment
R40.0 does not map to an HCC and does not risk-adjust under CMS-HCC V28. That is normal — most ICD-10 codes do not. It still needs to be coded correctly; it just will not move a RAF score.
Medicare coverage
R40.0 is named in 29 Medicare coverage policies — 29 listing it as supporting medical necessity. Which of them applies to you depends on your Medicare contractor, and coverage genuinely differs by state.
- A54799Billing and Coding: Urine Drug Testing
- A55001Billing and Coding: Urine Drug Testing
- A56612Billing and Coding: CT of the Head
- A56614Billing and Coding: Psychiatric Inpatient Hospitalization
How R40.0 is indexed
Coders do not find codes by browsing the tabular list — they look them up in the alphabetic index, under the word the physician wrote. These are the index entries that lead here, so you can see which chart wordings map to R40.0.
- Drowsiness
- Somnolence
Code history
R40.0 has not changed since FY2024 — no addition, revision or deletion across the three most recent ICD-10-CM releases.
Related codes at this level
Codes that share R40. If R40.0 is not quite right, the correct code is usually one of these.
Questions about R40.0
- Is R40.0 a billable ICD-10-CM code?
- Yes. R40.0 is a billable, specific ICD-10-CM code and is valid for submission on a claim.
- Where does R40.0 sit in the tabular list?
- Symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R99), in the block Symptoms and signs involving cognition, perception, emotional state and behavior (R40-R46).
- What cannot be coded together with R40.0?
- R40.0 carries Excludes1 notes, which means the conditions they list can never be coded together with it on the same encounter. Some are written on the categories above R40.0 (R40) and apply to it just the same.