A39.84
BillablePostmeningococcal arthritis
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is A39.84 an HCC code?
Yes. A39.84 maps to Bone/Joint/Muscle Infections/Necrosis under the CMS-HCC V28 risk adjustment model (and Bone/Joint/Muscle Infections/Necrosis under V24).
HCC Category Mapping
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.
MEAT Criteria for A39.84
For A39.84 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 A39.84 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
A39.84 is the ICD-10-CM diagnosis code for postmeningococcal arthritis. This is joint inflammation that develops as a complication after a meningococcal infection (a serious bacterial infection). It typically occurs during recovery from meningococcal disease and affects one or more joints. A39.84 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering other bacterial diseases (a30-a49).
Under the CMS-HCC V28 risk adjustment model, A39.84 maps to Bone/Joint/Muscle Infections/Necrosis (HCC 92) with a community, non-dual, aged base RAF weight of 0.209. Under the older V24 model, A39.84 mapped to the same category but with a base RAF weight of 0.482 — 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 code should only be used when arthritis is documented as a direct complication following meningococcal infection; verify the causal relationship in the medical record. Because A39.84 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 A39.84 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This code should only be used when arthritis is documented as a direct complication following meningococcal infection; verify the causal relationship in the medical record
- •Code A39.84 is a post-infectious sequela, so ensure the meningococcal infection has been previously documented or is being treated concurrently; consider using a combination code approach if both conditions are active
Clinical Significance
Postmeningococcal arthritis is an immune-mediated reactive arthritis occurring after meningococcal infection, typically developing 5-10 days after acute illness. Unlike septic arthritis, the joint fluid is sterile and the condition is driven by immune complex deposition. It is generally self-limited but can cause significant morbidity.
Documentation Requirements
- ✓History of preceding meningococcal infection with subsequent joint inflammation
- ✓Temporal relationship documented — arthritis onset after the acute meningococcal episode
- ✓Sterile synovial fluid analysis (negative cultures) distinguishing from active septic arthritis
- ✓Joint(s) involved and clinical examination findings
- ✓Resolution timeline and treatment response (typically responds to anti-inflammatory therapy)