What is ICD-10 code E88.49?

E88.49 is the ICD-10-CM diagnosis code for Other mitochondrial metabolism disorders. Other rare mitochondrial metabolism disorders not classified elsewhere, affecting how cells produce and use energy. It belongs to the ICD-10-CM chapter for endocrine, nutritional and metabolic diseases (e00-e89). E88.49 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. E88.49 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. E88.49 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. E88.49 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 E88.49?

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. E88.49 was a payment HCC under V24 (Other Significant Endocrine and Metabolic Disorders) 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 E88.49?

Use this code for mitochondrial disorders that don't fit into the more specific categories (E88.40-E88.43) Always document the specific mitochondrial condition in the medical record to support medical necessity and allow for future specificity Because E88.49 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.

E88.49: Other mitochondrial metabolism disorders — ICD-10 | Other Significant Endocrine

ICD-10-CM Code View

HCC Buddy Code Card

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Code lookupE88.49Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Endocrine, nutritional and metabolic diseases (E00-E89) / Metabolic disorders (E70-E88)

E88.49

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

Other mitochondrial metabolism disorders

Other rare mitochondrial metabolism disorders not classified elsewhere, affecting how cells produce and use energy.

Buddy Insight

This code captures named mitochondrial metabolism disorders that do not have their own specific code, such as Leigh syndrome, Kearns-Sayre syndrome, NARP (Neuropathy, Ataxia, and Retinitis Pigmentosa), and other complex mitochondrial disorders.

CMS-HCC V28

Not risk-adjusted for this model/period.

RAF 0

CMS-HCC V24

Mapped

HCC 23

Other Significant Endocrine a...

RAF 0.230

ACA/HHS

Not risk-adjusted for this model/period.

RAF 0

ESRD/PACE

Mapped

HCC 23

Other Significant Endocrine a...

RAF 0.0

RXHCC

Mapped

HCC 43

Other Significant Endocrine a...

RAF 0.0

Code Trumping

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Code Book Path

Official

E88Other and unspecified metabolic disorders

E88.4Mitochondrial metabolism disorders

E88.49Other mitochondrial metabolism disorders

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for E88.49 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for E88.49 in this effective period.

Related Child Codes

Official

E88.40Mitochondrial metabolism disorder, unspecified

E88.41MELAS syndrome

E88.42MERRF syndrome

E88.43Disorders of mitochondrial tRNA synthetases

Includes

Official

ICD-10-CM does not list Includes notes for E88.49 in this effective period.

Excludes 1

Official

disorders of pyruvate metabolism (E74.4)
Kearns-Sayre syndrome (H49.81)
Leber's disease (H47.22)
Leigh's encephalopathy (G31.82)
Mitochondrial myopathy, NEC (G71.3)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for E88.49 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for E88.49 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for E88.49 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Specific named mitochondrial disorder documented (Leigh syndrome, Kearns-Sayre, NARP, etc.)

Genetic testing or clinical diagnostic criteria met

Affected organ systems and severity assessment

Multi-system evaluation results

MEAT Support

HCC Buddy guidance

Specific named mitochondrial disorder documented (Leigh syndrome, Kearns-Sayre, NARP, etc.)

Genetic testing or clinical diagnostic criteria met

Affected organ systems and severity assessment

Multi-system evaluation results

Audit Caution

HCC Buddy guidance

Using this code for MELAS, MERRF, or tRNA synthetase disorders which have their own codes

Defaulting to E88.40 (unspecified) when a named mitochondrial syndrome is documented

Not coding multi-system manifestations (seizures, cardiac, hearing loss) as separate conditions

Missing Kearns-Sayre syndrome in patients with progressive external ophthalmoplegia, retinopathy, and cardiac conduction defects

Common Mistakes

HCC Buddy guidance

E88.41 — MELAS syndrome: has its own specific code; do not use E88.49

E88.42 — MERRF syndrome: has its own specific code; do not use E88.49

E88.43 — Disorders of mitochondrial tRNA synthetases: has its own specific code

E88.40 — Mitochondrial metabolism disorder, unspecified: use only when the specific type is unknown

Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.

Is E88.49 an HCC code?

Yes. E88.49 maps to Other Significant Endocrine and Metabolic Disorders under the V24 model but is not retained in V28.

HCC Category Mapping

V24HCC 23, Other Significant Endocrine and Metabolic Disorders

0.230

ESRDHCC 23, Other Significant Endocrine and Metabolic Disorders

0.000

RxHCCHCC 43, Other Significant Endocrine and Metabolic Disorders

0.000

RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. 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 E88.49 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for E88.49

For E88.49to 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 E88.49 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

E88.49 is the ICD-10-CM diagnosis code for other mitochondrial metabolism disorders. Other rare mitochondrial metabolism disorders not classified elsewhere, affecting how cells produce and use energy. E88.49 sits in the ICD-10-CM chapter for endocrine, nutritional and metabolic diseases (e00-e89), within the section covering metabolic disorders (e70-e88).

Under the older CMS-HCC V24 model, E88.49 maps to Other Significant Endocrine and Metabolic Disorders (HCC 23) with a community, non-dual, aged base RAF weight of 0.230. 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.

Use this code for mitochondrial disorders that don't fit into the more specific categories (E88.40-E88.43). Because E88.49 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 E88.49 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Use this code for mitochondrial disorders that don't fit into the more specific categories (E88.40-E88.43)
•Always document the specific mitochondrial condition in the medical record to support medical necessity and allow for future specificity

Clinical Significance

Documentation Requirements

✓Specific named mitochondrial disorder documented (Leigh syndrome, Kearns-Sayre, NARP, etc.)
✓Genetic testing or clinical diagnostic criteria met
✓Affected organ systems and severity assessment
✓Multi-system evaluation results
✓Current treatment and support measures
✓Documentation that the condition is NOT MELAS (E88.41), MERRF (E88.42), or tRNA synthetase disorder (E88.43)

Commonly Confused Codes

•E88.41: MELAS syndrome: has its own specific code; do not use E88.49
•E88.42: MERRF syndrome: has its own specific code; do not use E88.49
•E88.43: Disorders of mitochondrial tRNA synthetases: has its own specific code
•E88.40: Mitochondrial metabolism disorder, unspecified: use only when the specific type is unknown
•G71.3: Mitochondrial myopathy: when myopathy is the sole manifestation