OASIS

OASIS is the data set, not the visit. Under the home health conditions of participation, the agency’s full patient assessment has to include the current OASIS items, in their own wording and groupings. The assessment is due no later than 5 calendar days after the start of care, and is updated in the last 5 days of every 60 days from the start of care, within 48 hours of the patient’s return home from a hospital admission of 24 hours or more, and at discharge². Each completed assessment has to be encoded and transmitted to CMS within 30 days³. CMS publishes the instrument by version: OASIS-E1 took effect on January 1, 2025, and OASIS-E2 on April 1, 2026¹.

For billing, submitting the OASIS is a condition of payment. Under PDGM, Medicare’s claims system takes the OASIS items used for grouping from iQIES and calculates the HIPPS code itself, so a claim that cannot be matched to an accepted assessment is returned to the provider. The match runs on three items: the agency’s CMS Certification Number (M0010), the Medicare beneficiary number (M0063) and the assessment completion date (M0090), which the claim reports with occurrence code 50⁴. The assessment also has to be one used for payment, with a reason for assessment in M0100 of 01, 03, 04 or 05.

The mistake is billing before the assessment is in. Check the final validation report first: the claim should not go out until it shows the OASIS accepted. When a patient’s Medicare number changes, update the assessment before resubmitting, or the claim and the OASIS will never match.