Q42.9
BillableCongenital absence, atresia and stenosis of large intestine, part unspecified
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is Q42.9 an HCC code?
Yes. Q42.9 maps to Intestinal Obstruction/Perforation under the CMS-HCC V28 risk adjustment model.
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 Q42.9
For Q42.9 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 Q42.9 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
Q42.9 is the ICD-10-CM diagnosis code for congenital absence, atresia and stenosis of large intestine, part unspecified. A birth defect where part of the large intestine is missing, closed off, or abnormally narrowed, but the specific location is not documented. Q42.9 sits in the ICD-10-CM chapter for congenital malformations, deformations, chromosomal abnormalities, and genetic disorders (q00-qa0), within the section covering other congenital malformations of the digestive system (q38-q45).
Under the CMS-HCC V28 risk adjustment model, Q42.9 maps to Intestinal Obstruction/Perforation (HCC 78) with a community, non-dual, aged base RAF weight of 0.000. Q42.9 was not retained as a payment HCC under the older V24 model, so V28 introduced or recategorized it during the 2024–2026 phase-in. 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.
Query the provider if the specific site (rectum, colon, ileocecal valve) is known, as more specific codes (Q42.0-Q42.8) may be more appropriate. Because Q42.9 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 Q42.9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
Clinical Significance
This unspecified congenital large intestine malformation code indicates significant structural abnormalities requiring specialized care but lacks anatomical specificity. It represents conditions that may require surgical intervention and lifelong management, making precise documentation crucial for appropriate care planning.
Documentation Requirements
- ✓Confirmation of congenital nature of the condition
- ✓Evidence of absence, atresia, or stenosis of large intestine
- ✓Reason why specific anatomical location cannot be determined
- ✓Associated symptoms or complications
- ✓Surgical interventions performed or planned
- ✓Current functional status of bowel function
- ✓Any diagnostic imaging or studies performed