S06.5XAA Traumatic Subdural: V28 HCC 399; LOC Picks 397, 398, or 399

If you searched S06.5XAA, here is the short answer. S06.5XAA (Traumatic subdural hemorrhage with loss of consciousness status unknown, initial encounter) is a billable code that maps to CMS-HCC V28 HCC 399 (Major Head Injury without Loss of Consciousness). The PY2026 V28 CSV on HCC Buddy main has the row `S065XAA,399.0,,,`, the V28 column of the CMS 2027 Initial ICD-10-CM Mappings (payment year 2027, 2026 dates of service) lists 399 for it, and the live card shows HCC 399.

Two parts of the code decide the V28 result for a traumatic subdural hemorrhage. The 6th character records loss of consciousness (LOC), and it moves the code between HCC 397, HCC 398, and HCC 399. The 7th character records the encounter, and only the initial encounter codes ending in A have a V28 row. The subsequent encounter (D) and sequela (S) versions of the same codes have no V28 HCC.

The S06.5 codes, descriptors, and Tabular notes are the same in the FY2026 and FY2027 files, and the FY2027 Tabular and Index addenda have no entries for S06.5.

Desk table: S06.5X, initial encounter

S06.5, S06.5X, and S06.5XA are nonbillable headings, and the live cards say so. The PY2026 V28 CSV has no row for S06.5X7A or S06.5X8A, and neither code appears in the CMS 2026 Final or 2027 Initial ICD-10-CM Mappings file.

Unknown is not the same as unspecified

The two codes for an uncertain loss of consciousness land in different categories, and this is the most common place a desk gets the HCC wrong.

• S06.5XAA, loss of consciousness status unknown, maps to HCC 399, the same category as S06.5X0A (without loss of consciousness). The Tabular lists "Traumatic subdural hemorrhage NOS" as an inclusion term under S06.5XA, so a traumatic subdural hemorrhage documented with no word about consciousness lands here.
• S06.5X9A, loss of consciousness of unspecified duration, maps to HCC 398. Use it when the provider documents that the patient lost consciousness but does not document how long.

The difference is in the provider's words. A note saying it is unknown whether the patient lost consciousness and a note saying the patient lost consciousness for an undocumented length of time record different facts. If the note is unclear, ask the provider. Do not choose a 6th character to reach a category.

Only the initial encounter maps

All 173 S06 rows in the PY2026 V28 CSV end in A. Not one S06 row ends in D or S. For this family, the live cards agree:

The 7th character follows the treatment, not the provider. Section I.C.19.a says the "7th character "A", initial encounter is used for each encounter where the patient is receiving active treatment for the condition." It says 7th character "D" "is used for encounters after the patient has completed active treatment of the condition and is receiving routine care for the condition during the healing or recovery phase." It also says the assignment of the 7th character "is based on whether the patient is undergoing active treatment and not whether the provider is seeing the patient for the first time."

So a follow-up office visit after the hospital stay usually carries a D code if the provider documents routine care during recovery, and a D code has no V28 HCC. If the provider documents that the patient is still receiving active treatment for the hemorrhage, the A code is correct for that visit. Code what the note supports, and never pick A because it maps.

The S06 category note also says that 7th characters D and S "do not apply" to codes with 6th character 7 or 8, the codes for death before regaining consciousness. Those codes exist only with A.

Sequela: the residual comes first

Section I.B.10 says a sequela "is the residual effect (condition produced) after the acute phase of an illness or injury has terminated." Section I.C.19.a says that with 7th character "S", "it is necessary to use both the injury code that precipitated the sequela and the code for the sequela itself," and that the specific type of sequela "is sequenced first, followed by the injury code."

S06.5XAS and the other S06.5 sequela codes have no V28 HCC. Whether the encounter carries an HCC depends on the residual condition the provider documents, so check that code on its own card.

The CSV rows behind the answer

Each initial encounter code in the desk table has one row in the PY2026 V28 CSV, with no age or sex condition. The rows sit together in the file:

• `S065X0A,399.0,,,`
• `S065X1A,398.0,,,`
• `S065X2A,398.0,,,`
• `S065X3A,397.0,,,`
• `S065X4A,397.0,,,`
• `S065X5A,397.0,,,`
• `S065X6A,397.0,,,`
• `S065X9A,398.0,,,`
• `S065XAA,399.0,,,`

The columns are ICD10, CC, MCE_AGE_CONDITION, AGE_EDIT_CONDITION, and SEX_EDIT_CONDITION. There is no row for S065X7A, S065X8A, or any S06.5 code ending in D or S.

The CMS 2026 Final and 2027 Initial ICD-10-CM Mappings agree. They list the same V28 category for each A code and leave the V28 column blank for every S06.5 sequela code. This post covers the CMS-HCC V28 result only.

Same relative factors, three categories

The PY2026 V28 relative factors list HCC 397, HCC 398, and HCC 399 with the same value in every segment column. The CNA reference is 0.199 for each, and the COMMUNITY_ND value is 0.15 for each. These are community segment values, not member totals, and the segment a member is scored in depends on that member's enrollment data.

The category still matters for the hierarchy. In the V28 hierarchy file, the row `HCC397,HCC202,HCC398,HCC399,,,` shows that HCC 397 supersedes HCC 202 (Coma, Brain Compression/Anoxic Damage), HCC 398, and HCC 399. The row `HCC398,HCC202,HCC399,,,,` shows that HCC 398 supersedes HCC 202 and HCC 399. The row `HCC399,,,,,,` shows that HCC 399 supersedes nothing. So two head injury codes in the same year count once, in the highest of the three categories.

The live hubs list HCC 397 with 76 codes, HCC 398 with 57, and HCC 399 with 189. Every code in HCC 397 and HCC 398 is an S06 code. HCC 399 also holds S02 fracture codes and one newborn birth injury code.

Traumatic or nontraumatic: the Index default flips

The other big decision is whether the bleed is traumatic. The answer comes from the provider, and the two families map to different categories.

HCC 248 is Intracranial Hemorrhage, with a CNA reference of 0.239 in the PY2026 V28 relative factors. The I62 codes have no 7th character.

Watch the main term in the FY2027 Alphabetic Index, because the default is different:

• Hematoma, subdural (traumatic) says to see Injury, intracranial, subdural hemorrhage, which goes to S06.5X-. The subterm nontraumatic says to see Hemorrhage, intracranial, subdural.
• Hemorrhage, subdural (acute) (nontraumatic) says to see Hemorrhage, intracranial, subdural, which goes to I62.00, with acute at I62.01, subacute at I62.02, and chronic at I62.03. Under that entry, the subterm traumatic says to see Injury, intracranial, subdural hemorrhage.

The I60-I69 block has an Excludes1 note for "traumatic intracranial hemorrhage (S06.-)", so a subdural is coded as traumatic or nontraumatic, not both. When the note says "subdural" with no cause, or the cause is unclear, ask the provider. Do not choose a family because one maps on a follow-up visit and the other does not.

Neighbors coders mix up

Concussion. No S06.0 code has a V28 row. The S06.0 Excludes1 note sends concussion with other intracranial injuries classified in S06.1- to S06.6- to the specified intracranial injury, so a concussion with a traumatic subdural hemorrhage is coded in S06.5.

Brain compression and midline shift. S06.5 has a note to use an additional code, if applicable, "for traumatic brain compression or herniation (S06.A-)". S06.A has a Code first note for the underlying traumatic brain injury, including "traumatic subdural hemorrhage (S06.5-)". In FY2027 the Tabular adds "Traumatic midline shift of brain" as an inclusion term under S06.A, and the Index adds Shift, midline, brain at G93.5, with traumatic at S06.A0 and with herniation at S06.A1. Traumatic compression codes map to HCC 399. G93.5, the nontraumatic code, maps to HCC 202.

Coma. Section I.C.18.e says R40.20 "should be assigned when the underlying cause of the coma is not known, or the cause is a traumatic brain injury and the coma scale is not documented in the medical record." Section I.B.14 lists the coma scale among the items that may be taken from documentation by clinicians other than the patient's provider, such as an emergency medical technician. R40.20 maps to HCC 202, and the hierarchy rows above show that HCC 397 and HCC 398 supersede HCC 202.

Other bleeds. Epidural (S06.4) and traumatic subarachnoid (S06.6) codes follow the same LOC and 7th character pattern as S06.5. Check each code on its own card.

MEAT for a traumatic subdural hemorrhage

For an S06.5 initial encounter code, the note should support the injury as current and under active treatment, not just a line in the history:

• M Monitor: the course of the hemorrhage and the neurologic status as the provider follows them
• E Evaluate: the imaging or exam results the provider reviewed at the visit
• A Assess: the hemorrhage named as traumatic, with the provider's statement about loss of consciousness
• T Treat: the active treatment the provider documents for the hemorrhage

MEAT is a review mnemonic, not a universal CMS coding rule. Follow the applicable coding, encounter, program, and payer requirements. See MEAT.

Reporting rules that apply

Section I.B.14 says "Code assignment is based on the documentation by the patient's provider". The LOC duration is not on the I.B.14 list of exceptions, so take it from the provider's note. If an emergency services record and the provider's note disagree, ask the provider.

In outpatient and office visits, Section IV.J says: "Code all documented conditions that coexist at the time of the encounter/visit and that require or affect patient care, treatment or management." Section IV.H says not to code diagnoses documented as "probable", "suspected," or with other terms of uncertainty, and to code "to the highest degree of certainty for that encounter/visit".

Audit and query traps

1. Treating LOC status unknown (S06.5XAA, HCC 399) and LOC of unspecified duration (S06.5X9A, HCC 398) as the same code.

2. Choosing a 6th character from an emergency services record when the provider's note says something different.

3. Coding A on a follow-up visit because it maps, when the provider documents routine care during recovery. Section I.C.19.a ties A to active treatment.

4. Expecting an HCC from a D or S code in S06. No S06 row in the V28 CSV ends in D or S.

5. Picking traumatic or nontraumatic without the provider stating the cause. The Index default for "hematoma" and "hemorrhage" is different.

6. Reporting a concussion code with an S06.5 code. The S06.0 Excludes1 note sends that to the specified injury.

7. Coding G93.5 for a traumatic midline shift. The FY2027 Index sends traumatic shift to S06.A0.

8. Using a CNA reference as a member RAF total, or forgetting that HCC 397 and HCC 398 supersede HCC 399.

9. Inventing Coding Clinic quotes, competitor comparisons, or PHI examples.

Two-minute check

1. Does the provider call the subdural traumatic or nontraumatic?

2. For a traumatic bleed, what does the provider say about loss of consciousness: none, a duration, unspecified duration, or unknown?

3. Is the patient receiving active treatment at this encounter (A), routine recovery care (D), or is this a sequela (S)?

4. Expect HCC 397 for LOC of 1 hour or more with survival, HCC 398 for shorter or unspecified duration, and HCC 399 for no LOC or status unknown. Expect no V28 HCC for D, S, or death before regaining consciousness. Expect HCC 248 for I62.0-.

5. Confirm the map on the live card and the CSV row. Confirm MEAT for this year.

Related desks and tools

• Live cards: S06.5XAA, S06.5X0A, S06.5X9A, S06.5X3A, S06.5XAD, S06.5XAS, I62.03, S06.A0XA, R40.20
• Hubs: HCC 397, HCC 398, HCC 399, HCC 248, HCC 202
• Lookup: ICD-10 to HCC, Encoder
• Evidence habits: MEAT, Excludes1 vs Excludes2, provider query templates, acute vs history of
• Nearby: acute stroke vs history of stroke, codes that do not map, FY2027 code changes

Sources

• Live HCC Buddy ICD-10-CM cards (FY2027 Tabular display) and the V28 HCC 397, 398, 399, 248, and 202 hubs, fetched October 30, 2026
• FY2026 and FY2027 ICD-10-CM order file billable flags, the FY2026 and FY2027 Tabular, the FY2027 Alphabetic Index, and the FY2027 Tabular and Index addenda
• CMS, FY2027 ICD-10-CM Official Guidelines for Coding and Reporting, Sections I.B.10, I.B.14, I.C.18.e, I.C.19.a, IV.H, and IV.J
• PY2026 V28 mapping, hierarchy, and relative factor files on HCC Buddy main
• CMS, ICD-10 codes (FY2027 ICD-10-CM code files and addendum, effective October 1, 2026)
• CMS, 2026 Model Software/ICD-10 Mappings (PY2026 V28 mappings, hierarchies, relative factors, and the 2026 Final ICD-10-CM Mappings)
• CMS, 2027 Model Software/ICD-10 Mappings (2027 Initial ICD-10-CM Mappings, payment year 2027, 2026 dates of service, shown on the live cards)

V28 mappings come from the cited live code pages and the PY2026 V28 CSV. Coefficients are source-labeled references, not member totals. Not medical advice. Not a Coding Clinic reprint.

Current as of October 30, 2026. Always confirm the PY2026 V28 CSV and the live code card before you lock a map claim.