OASIS
OASIS (Outcome and Assessment Information Set) is the standardized patient assessment data set that Medicare-certified home health agencies must collect for adult Medicare and Medicaid patients receiving skilled care. Completed at defined time points across the episode, OASIS data drives payment under PDGM, quality measures, star ratings, and value-based purchasing adjustments. The current version is OASIS-E2, effective April 1, 2026.
When OASIS is collected
OASIS is collected at specific time points, each with its own reason for assessment: start of care, resumption of care after an inpatient stay, recertification during the last five days of each 60-day certification period, other follow-up, transfer to an inpatient facility, death at home, and discharge. Only an RN, physical therapist, occupational therapist, or speech-language pathologist may complete an OASIS assessment. LPNs, therapy assistants, aides, and social workers cannot. One clinician completes each assessment based on their own observation of the patient, not a chart review by committee.
How OASIS drives payment under PDGM
Under PDGM (the Patient-Driven Groupings Model), each 30-day payment period is assigned to one of 432 case-mix groups. OASIS responses set the functional impairment level (low, medium, or high) from the M1800-series items, one of the model's core dimensions alongside admission source, timing, clinical grouping, and comorbidity adjustment. The diagnoses documented during assessment also feed the claim that determines clinical grouping. A handful of inaccurate answers can shift the HIPPS code and change reimbursement for the period, in either direction.
How OASIS drives quality scores and HHVBP
OASIS-based measures feed the Home Health Quality Reporting Program, the Quality of Patient Care Star Rating on Care Compare, and the expanded Home Health Value-Based Purchasing (HHVBP) model, where payment adjustments run up to plus or minus 5% of Medicare fee-for-service payments. In the CY2026 HHVBP measure set, OASIS-based measures account for 40% of the Total Performance Score. OASIS data also powers risk adjustment, so inaccurate assessments distort both your outcomes and the expected values you are judged against.
What good OASIS practice looks like
High-performing agencies treat OASIS as a clinical activity with financial consequences, not paperwork:
- Assess function by observing the patient perform tasks, not by interview alone
- Keep OASIS answers consistent with the visit note and plan of care
- Run a QA review before submission, focusing on payment- and measure-sensitive items
- Submit through iQIES within 30 days of the assessment completion date (M0090)
- Train clinicians on the current OASIS guidance manual, and retrain at every version change
Frequently asked questions
Who is allowed to complete an OASIS assessment?
An RN, physical therapist, occupational therapist, or speech-language pathologist. LPNs, PTAs, COTAs, home health aides, and MSWs may contribute care but cannot complete the OASIS. The assessing clinician answers items based on their own assessment of the patient.
Which patients require OASIS collection?
Skilled Medicare and Medicaid home health patients age 18 and older. Patients under 18, patients receiving maternity services, and patients receiving only personal care, housekeeping, or chore services are excluded. Many agencies still complete OASIS on other payers for consistency and quality tracking.
How quickly must OASIS be submitted?
Within 30 days of the assessment completion date recorded in M0090. Submissions go through iQIES, CMS's internet Quality Improvement and Evaluation System. Late or missing submissions create compliance exposure and can hold up billing.