Q93.1
BillableWhole chromosome monosomy, mosaicism (mitotic nondisjunction)
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is Q93.1 an HCC code?
No. Q93.1 is a billable ICD-10-CM code but does not map to any HCC category in V28, V24, ESRD, or RxHCC.
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 Q93.1
For Q93.1to 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 Q93.1 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
Q93.1 is the ICD-10-CM diagnosis code for whole chromosome monosomy, mosaicism (mitotic nondisjunction). A chromosomal condition where a person is missing an entire chromosome in some cells but not others (mosaic pattern), with the missing chromosome affecting only a portion of body cells. Q93.1 sits in the ICD-10-CM chapter for congenital malformations, deformations, chromosomal abnormalities, and genetic disorders (q00-qa0), within the section covering chromosomal abnormalities, not elsewhere classified (q90-q99).
Q93.1 is a billable ICD-10-CM code but does not map to a payment HCC under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can be reported on Medicare Advantage encounter data submissions but it does not contribute to a beneficiary's RAF score and therefore does not affect risk-adjusted payments to the plan.
This code maps to RxHCC 148 (Mild Intellectual Disabilities) with a RAF weight of 0.0 in the RxHCC model. While it doesn't affect risk adjustment scoring, it identifies patients who may require specialized medications for developmental delays, seizures, or other complications associated with chromosomal mosaicism.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for Q93.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Mosaicism may result in milder phenotype compared to non-mosaic monosomy
- •Document which chromosome is affected and the percentage of affected cells if available
Clinical Significance
Mosaic whole chromosome monosomy indicates that some cells are missing an entire chromosome while others have the normal complement, typically resulting in less severe but still significant developmental abnormalities and intellectual disabilities. The clinical severity depends on the percentage of affected cells and which tissues are involved.
Documentation Requirements
- ✓Karyotype analysis showing mosaic pattern
- ✓Percentage of cells affected if documented
- ✓Specific chromosome involved
- ✓Mitotic nondisjunction mechanism noted
- ✓Clinical manifestations in affected individual
- ✓Developmental assessment results
- ✓Associated abnormalities or anomalies
- ✓Genetic counseling documentation