M08.421 ICD-10-CM Code: Pauciarticular juvenile rheumatoid arthritis, right elbow
M08.421 maps to CMS-HCC V28 93. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC Buddy coding tools
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FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Inflammatory polyarthropathies (M05-M14)
M08.421
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidancePauciarticular juvenile rheumatoid arthritis, right elbow
A type of arthritis in children that affects only a few joints, specifically involving the right elbow. It causes inflammation and stiffness in the elbow joint.
Buddy Insight
Pauciarticular juvenile rheumatoid arthritis affecting the right elbow represents a chronic inflammatory condition that can significantly impact upper extremity function and activities of daily living.
CMS-HCC V28
MappedHCC 93
Coefficient HCC 93: 0.617 (Community Non-Dual Aged (CNA))
CMS-HCC V24
HistoricalHistorical
Not used for CY2026 payment
ACA/HHS
MappedHCC 056
Code-level coefficient reference
ESRD/PACE
MappedHCC 40
Code-level coefficient reference
RXHCC
MappedHCC 83
Code-level coefficient reference
Code Book Path
Inclusion Terms
OfficialNo inclusion terms are included in this display for M08.421. Check the code and parent instructions in the Code Book.
Excludes 2
Official- arthropathic psoriasis (L40.5-)Inherited from M00-M99
- certain conditions originating in the perinatal period (P04-P96)Inherited from M00-M99
- certain infectious and parasitic diseases (A00-B99)Inherited from M00-M99
- compartment syndrome (traumatic) (T79.A-)Inherited from M00-M99
- complications of pregnancy, childbirth and the puerperium (O00-O9A)Inherited from M00-M99
- congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)Inherited from M00-M99
- endocrine, nutritional and metabolic diseases (E00-E88)Inherited from M00-M99
- injury, poisoning and certain other consequences of external causes (S00-T88)Inherited from M00-M99
- neoplasms (C00-D49)Inherited from M00-M99
- symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)Inherited from M00-M99
Related Codes
Includes
OfficialNo Includes notes are included in this display for M08.421. Check the code and parent instructions in the Code Book.
Excludes 1
Official- arthropathy in Whipple's disease (M14.8)Inherited from M08
- Felty's syndrome (M05.0)Inherited from M08
- juvenile dermatomyositis (M33.0-)Inherited from M08
- psoriatic juvenile arthropathy (L40.54)Inherited from M08
Code First
OfficialNo Code First sequencing instructions are included in this display for M08.421. Check the code and parent instructions in the Code Book.
Use Additional
OfficialNo Use Additional Code instructions are included in this display for M08.421. Check the code and parent instructions in the Code Book.
Code Also
Official- any associated underlying condition, such as:Inherited from M08
- regional enteritis [Crohn's disease] (K50.-)Inherited from M08
- ulcerative colitis (K51.-)Inherited from M08
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
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 M08.421 an HCC code?
Yes. M08.421 (Pauciarticular juvenile rheumatoid arthritis, right elbow) maps to HCC 93, Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.617. 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. It is billable for payment year 2026.
Coder answer: M08.421 is billable and maps to V28 HCC 93, Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- M08.421
- Description
- Pauciarticular juvenile rheumatoid arthritis, right elbow
- HCC (V28)
- HCC 93 — Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders
- RAF reference coefficient
- 0.617
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. 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 context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.
Work M08.421 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →
MEAT review for M08.421
For M08.421, 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.
- 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
Coder workflow notes
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What This Code Means
M08.421 is the ICD-10-CM diagnosis code for pauciarticular juvenile rheumatoid arthritis, right elbow. A type of arthritis in children that affects only a few joints, specifically involving the right elbow. It causes inflammation and stiffness in the elbow joint. M08.421 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering inflammatory polyarthropathies (m05-m14).
Under the CMS-HCC V28 risk adjustment model, M08.421 maps to Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders (HCC 93) with a source-labeled community, non-dual, aged reference coefficient of 0.617. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. 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.
Ensure the medical record clearly documents right elbow involvement before assigning this code. For M08.421, 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. 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, source-labeled coefficient references, and MEAT documentation criteria for M08.421 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Ensure the medical record clearly documents right elbow involvement before assigning this code
- •Remember that pauciarticular JIA typically affects 4 or fewer joints; document which other joints may be involved
Clinical Significance
Pauciarticular juvenile rheumatoid arthritis affecting the right elbow represents a chronic inflammatory condition that can significantly impact upper extremity function and activities of daily living. This diagnosis requires ongoing rheumatologic management to prevent joint destruction, contractures, and growth abnormalities, with potential need for orthopedic intervention and rehabilitation services.
Documentation Requirements
- ✓Patient age at onset (must be under 16 years)
- ✓Involvement of 4 or fewer joints throughout disease course
- ✓Documentation of right elbow joint involvement with inflammation
- ✓Absence of systemic symptoms (fever, rash, organomegaly)
- ✓Duration of symptoms (minimum 6 weeks for JRA diagnosis)
- ✓Physical examination findings of elbow joint swelling, warmth, or limited motion
- ✓Laboratory studies excluding other causes of arthritis
- ✓Assessment of functional impact on upper extremity use and range of motion
Commonly Confused Codes
- •M08.3: Juvenile rheumatoid polyarthritis seronegative (affects 5 or more joints)
- •M08.2x: Juvenile rheumatoid arthritis with systemic onset (has systemic symptoms)
- •M25.521: Pain in right elbow (symptom code, not diagnostic)
- •M24.821: Other specific joint derangements of right elbow (mechanical problems)
- •S53.101A: Unspecified dislocation of right radial head, initial encounter (traumatic injury)