Question 1

What is ICD-10 code M86.639?

Accepted Answer

M86.639 is the ICD-10-CM diagnosis code for Other chronic osteomyelitis, unspecified radius and ulna. A chronic bone infection in the forearm bones (radius and ulna) where the specific side is not identified or documented. M86.639 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. M86.639 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.

Question 2

Is M86.639 an HCC code?

Accepted Answer

Yes. The final FY2026 CMS mapping file maps M86.639 to HCC 92 (Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis) under CMS-HCC V28 with source-labeled reference coefficients HCC 92 0.479.  Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

Question 3

Is M86.639 billable?

Accepted Answer

Yes. M86.639 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. M86.639 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.

Question 4

Which HCC does M86.639 map to under V28?

Accepted Answer

M86.639 maps to CMS-HCC V28 HCC 92 (Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis).  The category numbers, labels, and conditions come from the CMS-HCC V28 model file for payment year 2026.

Question 5

What RAF reference is published for M86.639?

Accepted Answer

M86.639 has source-labeled community, non-dual, aged reference coefficients HCC 92 0.479 under CMS-HCC V28 for payment year 2026.  The coefficients come from the CMS V28 relative-factor file. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

Question 6

What is the V28 vs V24 difference for M86.639?

Accepted Answer

For M86.639, the current CMS-HCC V28 result is HCC 92 (Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis). Select a historical effective period before comparing a V24 mapping.  Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

Question 7

What documentation supports M86.639?

Accepted Answer

This is a less specific code; attempt to clarify laterality through provider query when possible Use only when medical record does not specify right or left forearm involvement For M86.639, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. See the MEAT criteria checklist at /meat-criteria for what Monitor, Evaluate, Assess, or Treat looks like in a note. One mnemonic element does not establish that a diagnosis is reportable.

Question 8

Can M86.639 be a primary diagnosis?

Accepted Answer

Yes. M86.639 carries no code-first instruction in the FY2026 tabular, so it can be the first-listed diagnosis when it is the condition chiefly responsible for the encounter and the note supports it, and it can also be reported as a secondary diagnosis. For risk adjustment the order does not matter; the V28 category is the same either way.

Question 9

Which codes cannot be reported with M86.639?

Accepted Answer

The Excludes1 note that applies to M86.639 lists postprocedural osteopathies (M96.-); osteomyelitis due to: echinococcus (B67.2); gonococcus (A54.43); salmonella (A02.24). An Excludes1 condition is not reported together with M86.639; report one or the other, unless the two conditions are unrelated, which the ICD-10-CM Official Guidelines (Section I.A.12.a) allow. The Excludes2 note lists arthropathic psoriasis (L40.5-); certain conditions originating in the perinatal period (P04-P96); certain infectious and parasitic diseases (A00-B99); compartment syndrome (traumatic) (T79.A-); and 9 more (see the notes on this page); those are separate conditions that may be reported together with M86.639 when both are documented.

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M86.639 ICD-10-CM Code: Other chronic osteomyelitis, unspecified radius and ulna

HCC Buddy Code Card

M86.639

Is M86.639 an HCC code?

HCC Category Mapping

MEAT review for M86.639

Get the V28 mapping + MEAT cheat sheet

What This Code Means

Coding Tips

Clinical Significance

Documentation Requirements

Commonly Confused Codes

Child Codes

Code Hierarchy

Also searched as

Work M86.639 in HCC Buddy