J66.0
BillableByssinosis
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is J66.0 an HCC code?
Yes. J66.0 maps to Chronic Obstructive Pulmonary Disease, Interstitial Lung Disorders, and Other Chronic Lung Disorders under the CMS-HCC V28 risk adjustment model (and Fibrosis of Lung and Other Chronic Lung Disorders 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 J66.0
For J66.0to 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 J66.0 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
J66.0 is the ICD-10-CM diagnosis code for byssinosis. A lung disease affecting textile workers exposed to cotton, flax, or hemp dust, causing airway obstruction and breathing difficulties. Symptoms often worsen on the first day back to work after time off. J66.0 sits in the ICD-10-CM chapter for diseases of the respiratory system (j00-j99), within the section covering lung diseases due to external agents (j60-j70).
Under the CMS-HCC V28 risk adjustment model, J66.0 maps to Chronic Obstructive Pulmonary Disease, Interstitial Lung Disorders, and Other Chronic Lung Disorders (HCC 280) with a community, non-dual, aged base RAF weight of 0.319. Under the older CMS-HCC V24 model, J66.0 maps to Fibrosis of Lung and Other Chronic Lung Disorders (HCC 112) with a community, non-dual, aged base RAF weight of 0.219. 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.
Confirm occupational exposure to cotton, flax, or hemp dust in textile manufacturing or processing. Because J66.0 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 J66.0 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Confirm occupational exposure to cotton, flax, or hemp dust in textile manufacturing or processing
- •Document the characteristic 'Monday fever' pattern if present, as it helps confirm the diagnosis
Clinical Significance
Byssinosis is an important occupational airway disease in textile workers that can progress from reversible Monday morning chest tightness to irreversible chronic obstructive pulmonary disease. It is significant for risk adjustment because it represents a chronic respiratory condition requiring ongoing management, workplace modification counseling, and pulmonary monitoring.
Documentation Requirements
- ✓Documented occupational exposure to cotton, flax, or hemp dust in textile manufacturing
- ✓Clinical staging of byssinosis (Grade 0 through Grade 3) if documented
- ✓Characteristic symptom pattern — worsening on first day of work week ('Monday fever')
- ✓Pulmonary function test results, particularly pre- and post-shift spirometry
- ✓Duration of exposure and current work status
- ✓Treatment plan and any work restrictions
Commonly Confused Codes
- •J66.1 (Flax-dressers' disease) — specific to flax processing; byssinosis is broader and includes cotton and hemp
- •J44.1 (Chronic obstructive pulmonary disease with acute exacerbation) — if byssinosis has progressed to COPD, code the COPD; but early byssinosis is distinct
- •J45.x (Asthma codes) — byssinosis can mimic occupational asthma but has distinct pathophysiology
- •J66.8 (Airway disease due to other specific organic dusts) — use J66.0 specifically for cotton/flax/hemp textile dust