What is ICD-10 code G61.1?

G61.1 is the ICD-10-CM diagnosis code for Serum neuropathy. Nerve damage that develops as a reaction to a serum injection or vaccine, causing inflammation and weakness in multiple nerves. It belongs to the ICD-10-CM chapter for diseases of the nervous system (g00-g99). G61.1 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. G61.1 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. G61.1 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. G61.1 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 G61.1?

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. G61.1 was a payment HCC under V24 (Myasthenia Gravis/Myoneural Disorders and Guillain-Barre Syndrome/Inflammatory and Toxic Neuropathy) but the V28 recalibration removed it from the risk adjustment model. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting G61.1?

Document the specific serum or vaccine that triggered the reaction when possible Link this diagnosis to the administration of the causative serum or vaccine for complete clinical picture Because G61.1 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 G61.1: Serum neuropathy

ICD-10-CM Code View

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Code lookupG61.1Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Diseases of the nervous system (G00-G99) / Polyneuropathies and other disorders of the peripheral nervous system (G60-G65)

G61.1

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

Serum neuropathy

Nerve damage that develops as a reaction to a serum injection or vaccine, causing inflammation and weakness in multiple nerves.

Buddy Insight

Serum neuropathy is an immune-mediated nerve damage triggered by serum or vaccine administration, representing an adverse reaction that requires ongoing monitoring and treatment.

CMS-HCC V28

N/A

—

Not risk-adjusted for this model/period.

Not mapped

CMS-HCC V24

Mapped

HCC 75

Myasthenia Gravis/Myoneural D...

RAF 0.472

ACA/HHS

Mapped

HCC 115

HHS-HCC 115

Varies by metal level

ESRD/PACE

Mapped

HCC 75

Myasthenia Gravis/Myoneural D...

RAF 0.074

RXHCC

Mapped

HCC 158

Guillain-Barre Syndrome and O...

RAF 0.074

Code Book Path

Official

G61Inflammatory polyneuropathy

G61.1Serum neuropathy

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for G61.1 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for G61.1 in this effective period.

Related Child Codes

Official

G61.0Guillain-Barre syndrome

G61.8Other inflammatory polyneuropathies

G61.9Inflammatory polyneuropathy, unspecified

Includes

Official

ICD-10-CM does not list Includes notes for G61.1 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for G61.1 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for G61.1 in this effective period.

Use Additional

Official

code for adverse effect, if applicable, to identify serum (T50.-)

Code Also

Official

ICD-10-CM does not list Code Also instructions for G61.1 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Identification of the specific serum or vaccine that triggered the neuropathy

Temporal relationship between serum/vaccine administration and symptom onset

Clinical findings: weakness, numbness, nerve conduction study results

Distinction from other inflammatory polyneuropathies

MEAT Support

HCC Buddy guidance

Identification of the specific serum or vaccine that triggered the neuropathy

Temporal relationship between serum/vaccine administration and symptom onset

Clinical findings: weakness, numbness, nerve conduction study results

Distinction from other inflammatory polyneuropathies

Audit Caution

HCC Buddy guidance

Failing to assign an additional external cause code (T36-T50) to identify the specific serum or vaccine causing the adverse effect

Using G61.0 (Guillain-Barre syndrome) instead of G61.1 when the neuropathy is specifically serum-related

Not documenting the causal relationship between the serum administration and the onset of neuropathy

Missing the seventh character for the external cause code indicating initial, subsequent, or sequela encounter

Common Mistakes

HCC Buddy guidance

G61.0 — Guillain-Barre syndrome is an autoimmune polyneuropathy not specifically triggered by serum; use G61.1 when causally linked to serum/vaccine

G61.89 — Other inflammatory polyneuropathies should be used only when the specific cause is not serum-related

T50.Z95A — Adverse effect of vaccines initial encounter captures the adverse event itself, not the resulting neuropathy

G62.0 — Drug-induced polyneuropathy is for medication-caused neuropathy, not serum/vaccine-triggered

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 G61.1 an HCC code?

Yes. G61.1 maps to Myasthenia Gravis/Myoneural Disorders and Guillain-Barre Syndrome/Inflammatory and Toxic Neuropathy under the V24 model but is not retained in V28.

Code: G61.1
Description: Serum neuropathy
HCC (V28): No CMS-HCC V28 mapping
RAF: —
Billable: Yes
Payment year: 2026

HCC Category Mapping

V24HCC 75, Myasthenia Gravis/Myoneural Disorders and Guillain-Barre Syndrome/Inflammatory and Toxic Neuropathy

0.472

ESRDHCC 75, Myasthenia Gravis/Myoneural Disorders and Guillain-Barre Syndrome/Inflammatory and Toxic Neuropathy

0.074

RxHCCHCC 158, Guillain-Barre Syndrome and Other Polyneuropathies

0.074

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 G61.1 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for G61.1

For G61.1 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 G61.1 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

G61.1 is the ICD-10-CM diagnosis code for serum neuropathy. Nerve damage that develops as a reaction to a serum injection or vaccine, causing inflammation and weakness in multiple nerves. G61.1 sits in the ICD-10-CM chapter for diseases of the nervous system (g00-g99), within the section covering polyneuropathies and other disorders of the peripheral nervous system (g60-g65).

Under the older CMS-HCC V24 model, G61.1 maps to Myasthenia Gravis/Myoneural Disorders and Guillain-Barre Syndrome/Inflammatory and Toxic Neuropathy (HCC 75) with a community, non-dual, aged base RAF weight of 0.472. 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.

Document the specific serum or vaccine that triggered the reaction when possible. Because G61.1 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 G61.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Document the specific serum or vaccine that triggered the reaction when possible
•Link this diagnosis to the administration of the causative serum or vaccine for complete clinical picture

Clinical Significance

Serum neuropathy is an immune-mediated nerve damage triggered by serum or vaccine administration, representing an adverse reaction that requires ongoing monitoring and treatment. Capturing this diagnosis is important for risk adjustment as it reflects a patient with complex neurological needs and potential long-term disability. It also has implications for adverse event tracking and pharmacovigilance.

Documentation Requirements

✓Identification of the specific serum or vaccine that triggered the neuropathy
✓Temporal relationship between serum/vaccine administration and symptom onset
✓Clinical findings: weakness, numbness, nerve conduction study results
✓Distinction from other inflammatory polyneuropathies
✓Provider's explicit statement linking the neuropathy to serum/vaccine exposure
✓Current treatment and management plan

Use Additional Code

code for adverse effect, if applicable, to identify serum (T50.-)

Commonly Confused Codes

•G61.0: Guillain-Barre syndrome is an autoimmune polyneuropathy not specifically triggered by serum; use G61.1 when causally linked to serum/vaccine
•G61.89: Other inflammatory polyneuropathies should be used only when the specific cause is not serum-related
•T50.Z95A: Adverse effect of vaccines initial encounter captures the adverse event itself, not the resulting neuropathy
•G62.0: Drug-induced polyneuropathy is for medication-caused neuropathy, not serum/vaccine-triggered