Assessment & OASIS
Reviewed by Zach Newman · Last reviewed July 2026
OASIS is where clinical accuracy and reimbursement meet. Every Start of Care, recertification, and discharge runs through a comprehensive assessment whose answers drive the patient's outcome scores and the agency's payment. This glossary of OASIS terms defines the home health assessment language clinicians use every day, from Section GG and the drug regimen review to OASIS-E1 and the 5-day assessment window.
25 terms5-Day Assessment Window
The 5-day assessment window is the regulatory deadline for completing the start of care comprehensive assessment, including the OASIS: within 5 days after the start of care date, where the SOC date counts as day 0. A parallel 5-day window applies at recertification, when the assessment must be completed during the last 5 days of each 60-day certification period.
BIMS (Brief Interview for Mental Status)
The BIMS (Brief Interview for Mental Status) is a short, standardized cognitive screening interview included in OASIS Section C. It tests word repetition, temporal orientation, and delayed recall, producing a summary score from 0 to 15 that stratifies patients as cognitively intact, moderately impaired, or severely impaired, and it aligns home health cognitive screening with the tools used in nursing facilities and other post-acute settings.
Comprehensive Assessment
The comprehensive assessment is the full patient evaluation that the Medicare Conditions of Participation require home health agencies to complete for every patient, regardless of payer. It must be completed within 5 days after the start of care date and includes clinical, functional, psychosocial, and medication content, a drug regimen review, and, for Medicare and Medicaid patients, the OASIS items.
Discharge Assessment
The discharge assessment is the OASIS completed when a patient is discharged from home health care, other than by death or transfer to an inpatient facility. It must be completed within 2 calendar days of the discharge date, and it captures the patient's end-of-care status that CMS compares against admission to calculate outcome measures.
Drug Regimen Review
The drug regimen review (DRR) is the required clinical screen of a home health patient's complete medication regimen for potentially clinically significant issues, such as interactions, duplications, omissions, adverse reactions, and noncompliance. It is part of the comprehensive assessment under the Conditions of Participation and is documented through OASIS items M2001, M2003, and M2005, which also feed a federal process measure.
Fall Risk Assessment
A fall risk assessment in home health is a structured screen of a patient's likelihood of falling, performed with a standardized, validated tool as part of the comprehensive assessment. OASIS item M1910 documents whether a multi-factor fall risk assessment was conducted, and falls with injury are captured at transfer and discharge, making fall risk both a clinical priority and a measured one.
GG Items (Functional Abilities)
GG items are the standardized functional ability items in Section GG of the OASIS, covering prior functioning, prior device use, self-care (GG0130), and mobility (GG0170). They score how much help a patient needs to complete everyday activities on a common 6-level scale used across home health, skilled nursing, inpatient rehab, and LTACH settings, and they feed federal quality measures.
ICD-10 Coding in Home Health
ICD-10 coding in home health is the assignment of diagnosis codes to each patient's episode, reported on the OASIS and the claim. Under PDGM, the principal diagnosis sets the clinical grouping and secondary diagnoses set the comorbidity adjustment, so coding accuracy directly determines payment, audit exposure, and how patient complexity appears in quality data.
M Items
M items are the OASIS data elements whose identifiers begin with M, the instrument's original numbering scheme, such as M0030 (start of care date), M1021 (primary diagnosis), and the M1800-series functional items. They remain the backbone of OASIS even as newer cross-setting sections with letter prefixes like GG, C, and D have been layered in.
Medication Reconciliation
Medication reconciliation is the process of comparing the medications a patient is actually taking against what is documented across sources, such as hospital discharge lists, practitioner orders, and pill bottles in the home, then resolving discrepancies. In home health it happens at start of care, after inpatient stays, and whenever orders change, and it is one of the highest-yield safety activities in the setting.
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.
OASIS Accuracy
OASIS accuracy is the degree to which OASIS responses reflect the patient's true status, assessed and coded according to CMS conventions. Because OASIS feeds PDGM payment, outcome measures, star ratings, HHVBP adjustments, and risk adjustment simultaneously, accuracy is the single control point where clinical documentation, revenue integrity, and quality performance converge.
OASIS Submission
OASIS submission is the electronic transmission of completed OASIS assessments to CMS through iQIES, the internet Quality Improvement and Evaluation System. Assessments must be submitted within 30 days of the assessment completion date, and timely, accepted submissions are a Condition of Participation, a quality reporting requirement, and a practical prerequisite for clean billing.
OASIS-E1
OASIS-E1 was the version of the Outcome and Assessment Information Set in effect from January 1, 2025 through March 31, 2026. It was a limited maintenance update to OASIS-E that added the COVID-19 vaccination item O0350 and retired items that had not been used for payment since PDGM began. OASIS-E2 replaced it on April 1, 2026.
OASIS-E2
OASIS-E2 is the current version of the Outcome and Assessment Information Set, effective for home health assessments completed on or after April 1, 2026. It replaced OASIS-E1 with a short list of item changes: M0069 (Gender) was replaced by A0810 (Sex), the A1250 transportation item was replaced by A1255, and the COVID-19 vaccination item O0350 was removed.
PHQ-2 and PHQ-9 in Home Health
The PHQ-2 and PHQ-9 (Patient Health Questionnaire) are standardized depression screening instruments embedded in OASIS Section D as the Patient Mood Interview (D0150). The two-question PHQ-2 acts as a gateway: patients who screen positive on the first two questions continue through the full nine-question PHQ-9, producing a severity score (D0160) that informs care planning and referrals.
Primary Diagnosis
The primary diagnosis is the ICD-10 code representing the condition most related to the patient's current home health plan of care, reported in OASIS item M1021 and as the principal diagnosis on the claim. Under PDGM, it assigns the 30-day period to one of 12 clinical groupings, making it one of the highest-leverage data points in the entire episode.
Recertification Assessment
The recertification assessment is the follow-up OASIS completed during the last 5 days of each 60-day certification period, days 56 through 60, when the patient will continue home health care into a new period. It updates the comprehensive assessment, supports the practitioner's recertification of eligibility, and informs the plan of care for the next 60 days.
Resumption of Care (ROC)
Resumption of Care (ROC) is the OASIS time point completed when a patient returns to home health services after an inpatient facility stay of 24 hours or more for reasons other than diagnostic tests. The ROC assessment must be completed within 2 calendar days of the patient's return home or the agency's knowledge of the return, and it reestablishes the clinical baseline after the hospitalization.
Risk Adjustment
Risk adjustment is the statistical method CMS uses to account for differences in patient characteristics when calculating home health outcome measures. Using OASIS and claims data, models predict each patient's expected outcome given their condition, and agencies are evaluated on observed performance relative to expected, so an agency serving sicker, more complex patients is not automatically penalized.
Secondary Diagnosis
Secondary diagnoses are the additional confirmed conditions, reported in OASIS item M1023 and on the claim, that coexist with the primary diagnosis and affect the patient's care. Under PDGM they determine the comorbidity adjustment, which can raise the 30-day period's case-mix weight when qualifying conditions or interacting condition pairs are present.
Section GG Self-Care and Mobility
Section GG self-care and mobility refers to the two core item sets within OASIS Section GG: GG0130, which scores self-care activities such as eating, oral hygiene, bathing, and dressing, and GG0170, which scores mobility activities from rolling in bed through walking distances and negotiating steps. Together they produce the standardized functional profile used in home health quality measurement.
Social Determinants of Health (SDOH)
Social determinants of health (SDOH) are the non-medical conditions that shape health outcomes, such as transportation access, health literacy, social isolation, language, and economic stability. OASIS collects standardized SDOH items, including ethnicity, race, preferred language, transportation (A1255 under OASIS-E2), health literacy, and social isolation, so home health agencies now assess and report these factors, not just notice them.
Start of Care (SOC)
Start of Care (SOC) is the date of the first billable visit in a home health episode, and the name of the OASIS assessment completed at that point. The SOC date anchors nearly every downstream deadline: the comprehensive assessment window, the Notice of Admission, the 60-day certification period, and the first 30-day PDGM payment period.
Transfer OASIS
A transfer OASIS is the assessment time point completed when a home health patient is admitted to an inpatient facility for 24 hours or more for reasons other than diagnostic tests. It comes in two forms: transfer without agency discharge, when the agency expects the patient back, and transfer with discharge, when the agency ends care. It must be completed within 2 calendar days of the transfer or of learning about it.
The EHR that does the work for you.
See how Enzo drafts the documentation, catches the errors, and closes the episode.