What is ICD-10 code B18.9?

B18.9 is the ICD-10-CM diagnosis code for Chronic viral hepatitis, unspecified. A long-term viral liver infection where the specific type of hepatitis virus has not been identified. It belongs to the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99). B18.9 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. B18.9 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. B18.9 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. B18.9 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What is the V28 vs V24 difference for B18.9?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For B18.9, V28 maps to Chronic Hepatitis at RAF 0.185 while V24 mapped to Chronic Hepatitis at RAF 0.147. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting B18.9?

This is a default code for chronic hepatitis when the virus type is unknown Pursue testing to identify the specific virus and update coding accordingly Because B18.9 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

2026 ICD-10-CM B18.9: Chronic viral hepatitis

ICD-10-CM Code View

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Code lookupB18.9Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Certain infectious and parasitic diseases (A00-B99) / Viral hepatitis (B15-B19)

B18.9

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Chronic viral hepatitis, unspecified

A long-term viral liver infection where the specific type of hepatitis virus has not been identified.

Buddy Insight

Chronic viral hepatitis, unspecified, is a default code used when a patient has documented chronic viral hepatitis but the specific virus has not been identified.

CMS-HCC V28

Mapped

HCC 65

Chronic Hepatitis

RAF 0.185

CMS-HCC V24

Mapped

HCC 29

Chronic Hepatitis

RAF 0.147

ACA/HHS

Mapped

HCC 37.2

HHS-HCC 37.2

Varies by metal level

ESRD/PACE

Mapped

HCC 29

Chronic Hepatitis

RAF 0.061

RXHCC

N/A

—

Not risk-adjusted for this model/period.

Not mapped

Code Book Path

Official

B18Chronic viral hepatitis

B18.9Chronic viral hepatitis, unspecified

Inclusion Terms

Official

Carrier of unspecified viral hepatitis

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for B18.9 in this effective period.

Related Child Codes

Official

B18.0Chronic viral hepatitis B with delta-agent

B18.1Chronic viral hepatitis B without delta-agent

B18.2Chronic viral hepatitis C

B18.8Other chronic viral hepatitis

Includes

Official

Carrier of viral hepatitis

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for B18.9 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for B18.9 in this effective period.

Use Additional

Official

code, if applicable, for ascites (R18.8)

Code Also

Official

ICD-10-CM does not list Code Also instructions for B18.9 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Documentation confirming chronic viral hepatitis (>6 months or stated as chronic)

Evidence that viral etiology testing has been performed or attempted

Explanation for why the specific virus type is unknown

Liver function tests and disease staging

MEAT Support

HCC Buddy guidance

Documentation confirming chronic viral hepatitis (>6 months or stated as chronic)

Evidence that viral etiology testing has been performed or attempted

Explanation for why the specific virus type is unknown

Liver function tests and disease staging

Audit Caution

HCC Buddy guidance

Using B18.9 when the specific virus is documented elsewhere in the record — always search for hepatitis serology results

Not querying the provider to identify the specific hepatitis virus for more accurate coding

Confusing viral hepatitis with autoimmune or drug-induced chronic hepatitis, which have different codes

Accepting the unspecified code without documenting why the virus type cannot be determined

Common Mistakes

HCC Buddy guidance

B18.1 (Chronic viral hepatitis B without delta) — If hepatitis B is confirmed, use the specific code

B18.2 (Chronic viral hepatitis C) — If hepatitis C is confirmed, use the specific code

K73.9 (Chronic hepatitis, unspecified) — Non-specific chronic hepatitis that may not be viral; B18.9 requires known viral etiology

B18.8 (Other chronic viral hepatitis) — For known viral agents other than B or C; B18.9 is for unknown virus type

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is B18.9 an HCC code?

Yes. B18.9 (Chronic viral hepatitis, unspecified) maps to Chronic Hepatitis under the CMS-HCC V28 risk adjustment model (and Chronic Hepatitis under V24), with a community non-dual aged RAF of 0.185. It is billable for payment year 2026.

Coder answer: B18.9 is billable and maps to V28 HCC 65, Chronic Hepatitis. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: B18.9
Description: Chronic viral hepatitis, unspecified
HCC (V28): HCC 65 — Chronic Hepatitis
RAF: 0.185
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 65, Chronic Hepatitis

0.185

V24HCC 29, Chronic Hepatitis

0.147

ESRDHCC 29, Chronic Hepatitis

0.061

Each model's RAF is its CMS base weight for that model's standard population, so weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.

Work B18.9 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for B18.9

For B18.9 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.

MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
EEvaluate: test results, medication response, or physical findings reviewed by the provider
AAssess: explicit mention in the assessment or plan with acknowledgment of status
TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed B18.9 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

B18.9 is the ICD-10-CM diagnosis code for chronic viral hepatitis, unspecified. A long-term viral liver infection where the specific type of hepatitis virus has not been identified. B18.9 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering viral hepatitis (b15-b19).

Under the CMS-HCC V28 risk adjustment model, B18.9 maps to Chronic Hepatitis (HCC 65) with a community, non-dual, aged base RAF weight of 0.185. Under the older V24 model, B18.9 mapped to the same category but with a base RAF weight of 0.147, V28 recalibrated weights across the entire model. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.

This is a default code for chronic hepatitis when the virus type is unknown. Because B18.9 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for B18.9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•This is a default code for chronic hepatitis when the virus type is unknown
•Pursue testing to identify the specific virus and update coding accordingly

Clinical Significance

Chronic viral hepatitis, unspecified, is a default code used when a patient has documented chronic viral hepatitis but the specific virus has not been identified. This code should trigger a provider query to determine the hepatitis type, as treatment, prognosis, and public health implications differ significantly between hepatitis B, C, and other viruses.

Documentation Requirements

✓Documentation confirming chronic viral hepatitis (>6 months or stated as chronic)
✓Evidence that viral etiology testing has been performed or attempted
✓Explanation for why the specific virus type is unknown
✓Liver function tests and disease staging
✓Plans for further diagnostic workup to identify the specific virus

Commonly Confused Codes

•B18.1 (Chronic viral hepatitis B without delta): If hepatitis B is confirmed, use the specific code
•B18.2 (Chronic viral hepatitis C): If hepatitis C is confirmed, use the specific code
•K73.9 (Chronic hepatitis, unspecified): Non-specific chronic hepatitis that may not be viral; B18.9 requires known viral etiology
•B18.8 (Other chronic viral hepatitis): For known viral agents other than B or C; B18.9 is for unknown virus type