Home Health OASIS Accuracy Audits: How Inaccurate Scoring Leads to PDGM Overpayments

Under the Patient-Driven Groupings Model (PDGM), Medicare pays home health agencies (HHAs) for each 30-day period of care based on patient characteristics. One of those characteristics, the functional impairment level, comes directly from the Outcome and Assessment Information Set (OASIS). That means a clinician's answers to a small set of OASIS items can move a payment period into a higher or lower payment group.

When OASIS scoring is accurate, payment reflects the patient's real needs. When scoring overstates a patient's impairment, Medicare may overpay. When it understates impairment, the agency may be underpaid and its quality scores may be distorted. Because OASIS answers are tied to payment, auditors compare OASIS responses with the rest of the medical record, and inconsistencies can lead to downcoding, overpayment demands, and in serious cases, fraud investigations.

This article explains how OASIS fits into PDGM, which items affect payment, how inaccurate scoring creates overpayments, what reviewers look for, and how agencies can audit and improve OASIS accuracy. It is educational and does not replace legal or professional advice.

OASIS Basics

OASIS is the standardized patient assessment data set that Medicare-certified HHAs must collect as part of the comprehensive assessment. Under the Conditions of Participation at 42 CFR 484.55, HHAs must complete a comprehensive assessment that accurately reflects the patient's current health status and includes OASIS data items. Under 42 CFR 484.45, HHAs must electronically report OASIS data to CMS.

CMS publishes the OASIS Guidance Manual, which explains how each item should be scored. Agencies should use the manual version in effect for the assessment date. CMS updates OASIS periodically, and the CY 2026 Home Health Prospective Payment System final rule removed several items and updated regulatory text to account for all-payer OASIS submission.

How PDGM Uses OASIS

Under PDGM, each 30-day period is assigned to one of 432 case-mix groups based on five factors:

• Admission source: community or institutional, based on Medicare claims history.

• Timing: early (the first 30-day period) or late (subsequent periods), based on claims history.

• Clinical grouping: one of 12 clinical groups, based on the principal diagnosis reported on the claim.

• Comorbidity adjustment: none, low, or high, based on secondary diagnoses reported on the claim.

• Functional impairment level: low, medium, or high, based on OASIS responses.

The functional impairment level is the factor driven by OASIS.

The OASIS Items That Drive the Functional Level

CMS's PDGM materials identify the OASIS items used to determine the functional impairment level. They include:

• M1800 Grooming.

• M1810 Current Ability to Dress Upper Body.

• M1820 Current Ability to Dress Lower Body.

• M1830 Bathing.

• M1840 Toilet Transferring.

• M1850 Transferring.

• M1860 Ambulation/Locomotion.

• M1033 Risk for Hospitalization.

Each response is assigned points. The points are added together, and the total places the period into a low, medium, or high functional impairment level within its clinical group. CMS updates the points and thresholds annually. The CY 2026 final rule updated functional impairment levels using CY 2024 data, and CMS has continued recalibrating with more recent data in the CY 2027 rulemaking.

Why a Few Points Matter

Because the functional level is determined by thresholds, a small change in one or two item responses can move a period from low to medium or from medium to high impairment. Higher functional impairment levels generally carry higher case-mix weights, so the change increases payment.

The OASIS-Claim Connection

The HHA submits the OASIS assessment to CMS and then submits the claim. The claim must correspond to the OASIS assessment, and the claim's case-mix group, reported as a Health Insurance Prospective Payment System (HIPPS) code, is determined using OASIS and claims information. Medical reviewers may adjust the HIPPS code if the medical record does not support the OASIS responses.

How Inaccurate Scoring Leads to Overpayments

Overstating Functional Impairment

If OASIS responses show more impairment than the patient actually has, the period may be placed in a higher functional level than appropriate. Examples:

• Scoring a patient as unable to dress the lower body when visit notes show the patient dresses independently.

• Scoring ambulation as requiring the assistance of another person when therapy notes show independent ambulation with a cane.

• Scoring bathing as dependent when the patient showers independently with a shower chair.

• Overstating risk for hospitalization factors without documentation.

Patterns That Signal Problems

• Functional scores that are consistently higher than peer agencies.

• Most patients falling in the high functional impairment level.

• Identical scores across many patients.

• Large improvements at discharge that seem implausible, suggesting admission scores were overstated.

• OASIS responses that conflict with clinical notes.

Understating Impairment

Understating impairment can cause underpayment and can also distort quality measures. While underpayment is not an overpayment risk, it reflects the same accuracy problem and should be corrected through training.

Consequences

• Medical reviewers may downcode the HIPPS code, creating an overpayment for the difference.

• Patterns of overstated scores may lead to targeted reviews, statistical sampling, and extrapolation.

• Intentional or reckless misstatement of OASIS data can lead to False Claims Act liability and other enforcement.

• Inaccurate OASIS data also affects quality reporting and the expanded Home Health Value-Based Purchasing Model.

What Auditors Look For

Consistency With the Clinical Record

Reviewers compare OASIS responses with:

• The comprehensive assessment narrative.

• Nursing and therapy visit notes.

• Aide care plans and notes.

• The plan of care.

• Practitioner and hospital records.

• Discharge assessments.

If an OASIS item says the patient needs help with lower body dressing, the record should show it.

Accuracy Under OASIS Guidance

Reviewers check whether responses follow the OASIS Guidance Manual's scoring conventions, such as scoring based on the patient's ability on the day of assessment, considering safety, and choosing the response that best describes the patient's ability.

Support for Risk for Hospitalization

M1033 responses should be supported by documentation of the identified risk factors, such as history of falls, unintentional weight loss, multiple hospitalizations, or other listed factors.

Timing and Assessment Rules

Reviewers check whether assessments were completed within required timeframes and by qualified clinicians, and whether the correct assessment type was used.

Running an OASIS Accuracy Audit

Step 1: Define the Scope

Choose a sample of start of care, resumption of care, and recertification assessments. Consider focusing on high-volume clinicians, new clinicians, high functional impairment periods, or outlier data.

Step 2: Select the Sample

For discovery, a probe sample may be sufficient. If results will be used to estimate overpayments, use a statistically valid random sample designed with a statistician, following principles similar to those in Chapter 8 of the Medicare Program Integrity Manual.

Step 3: Compare OASIS With the Record

For each assessment, compare the PDGM functional items and M1033 against the narrative and visit notes from the same period. Ask:

• Does the response follow OASIS guidance?

• Is it supported by the clinician's own narrative?

• Is it consistent with other disciplines' notes in the same timeframe?

• Is it consistent with the practitioner's and hospital records?

Step 4: Recalculate the Functional Level

Where responses are not supported, recalculate the functional points and determine whether the functional impairment level and HIPPS code would change.

Step 5: Quantify the Impact

Calculate the payment difference for each period where the level would change. Track overpayments and underpayments separately.

Step 6: Analyze Root Causes

Common causes include:

• Lack of training on OASIS conventions.

• Scoring based on what the patient says rather than observation.

• Scoring based on prior function or anticipated decline.

• Pressure, explicit or implied, to increase scores.

• EHR defaults or prompts that suggest higher scores.

• Copying prior assessments.

Step 7: Correct and Educate

Provide clinician-specific feedback, group training on high-error items, and competency testing. Review EHR templates. Reinforce that OASIS must reflect the patient's actual condition.

Step 8: Address Overpayments

If the audit shows claims were paid at a higher case-mix group than supported, evaluate obligations under the 60-day overpayment rule at 42 CFR 401.305 and work with counsel on investigation and repayment.

OASIS Review and Coding Review Processes

Many agencies use OASIS review before claim submission. These processes can improve accuracy if they are designed carefully.

• Reviewers should help clinicians apply OASIS guidance correctly, not push scores higher.

• Changes to OASIS responses should be made by the assessing clinician based on his or her own observations, with documentation explaining the change.

• Reviewers should flag inconsistencies in both directions.

• Agencies should monitor whether review processes systematically increase scores, which could be a compliance concern.

OIG's General Compliance Program Guidance emphasizes that compliance programs should address risks related to billing and coding accuracy. Pressure on clinicians to change assessments to increase payment can create serious legal risk.

Item-by-Item Accuracy Tips for the PDGM Functional Items

M1800 Grooming

• Consider all grooming tasks, such as washing face and hands, hair care, shaving or makeup, teeth or denture care, and fingernail care.

• Score based on what the patient can safely do, not what the patient usually chooses to do.

• Document the assistance observed or the reason the patient cannot safely perform the task.

M1810 and M1820 Upper and Lower Body Dressing

• Consider the patient's ability to obtain, put on, and remove clothing, including fasteners and footwear for lower body dressing.

• Observe the patient whenever possible rather than relying solely on report.

• Note devices and setup needs and how they affect the score.

M1830 Bathing

• Score the patient's ability to bathe the entire body, including getting in and out of the tub or shower, according to OASIS guidance.

• Distinguish between setup help, intermittent assistance, and the presence of another person throughout the task.

• Do not score based on the absence of a shower chair or other equipment without following the manual's conventions.

M1840 Toilet Transferring

• Score the ability to get to and from the toilet or commode and transfer on and off.

• Document devices and the level of assistance needed.

M1850 Transferring

• Score the ability to move safely between bed, chair, and standing.

• Document observed transfers and safety concerns.

M1860 Ambulation/Locomotion

• Score the ability to walk safely on a variety of surfaces once in a standing position, or to use a wheelchair if non-ambulatory, according to OASIS guidance.

• Coordinate with therapy observations when available.

M1033 Risk for Hospitalization

• Select only the risk factors supported by documentation, such as history of falls, unintentional weight loss, multiple hospitalizations or emergency department visits, decline in mental or functional status, difficulty complying with medical instructions, or taking multiple medications, as described on the item.

• Make sure each selected factor is documented elsewhere in the assessment or records.

Common OASIS Scoring Errors

• Scoring based on the patient's or family's report without observation when observation was possible.

• Scoring what the patient does by habit rather than what the patient can safely do.

• Scoring based on prior or anticipated function rather than function on the day of assessment.

• Selecting the more dependent response when the clinician is unsure, rather than following manual conventions.

• Inconsistent scoring between related items, such as ambulation and transferring.

• Failing to update scores at recertification and resumption of care.

• Allowing reviewers to change responses without clinician involvement.

Discharge Scores and the Bigger Picture

Accuracy at discharge matters too. Overstated admission scores combined with accurate discharge scores create the appearance of dramatic improvement. That pattern can inflate quality outcomes, affect the expanded Home Health Value-Based Purchasing Model, and suggest to reviewers that admission scores were overstated. Consistent, accurate scoring at every time point protects both payment and quality data.

Recertification and Resumption of Care Assessments

Recertification and resumption of care assessments also affect the functional level for later periods. Agencies should:

• Reassess the patient's actual current function rather than copying prior responses.

• Document improvements and declines.

• Make sure scores at recertification are consistent with visit notes from the preceding weeks.

Training Clinicians for Accuracy

• Train on the current OASIS Guidance Manual, especially the PDGM functional items and M1033.

• Use case studies and video scenarios for scoring practice.

• Test competency periodically and after manual updates.

• Teach clinicians to document observations that support each response in the narrative.

• Emphasize scoring the patient's actual ability on the day of assessment.

• Coordinate between nurses and therapists when both observe the patient.

Using Data to Monitor OASIS Accuracy

• Compare the agency's functional level distribution with state and national data.

• Compare individual clinicians' scoring patterns.

• Track changes in scores between start of care and discharge.

• Monitor for unusual increases after process or staffing changes.

• Review PEPPER and other CMS data reports where available.

Who Should Own OASIS Accuracy

OASIS accuracy is a shared responsibility.

• Clinicians are responsible for observing the patient and scoring accurately.

• Clinical managers are responsible for supervision, education, and case review.

• OASIS reviewers or coders support accuracy by flagging inconsistencies and questions.

• The compliance officer oversees auditing, monitoring, and response to findings.

• Leadership sets expectations that accuracy, not revenue, drives scoring.

Clear roles help prevent situations in which financial goals influence clinical assessments.

How OASIS Findings Show Up in Different Reviews

• MAC medical review and Targeted Probe and Educate: reviewers may adjust the HIPPS code when the record does not support the functional scores, resulting in partial denials.

• Review Choice Demonstration: reviewers focus primarily on eligibility, but inconsistencies between OASIS and the record can affect the review.

• Comprehensive Error Rate Testing: incorrect case-mix assignment contributes to improper payment estimates.

• UPICs: data showing outlier functional scores may prompt reviews, interviews, and sampling with extrapolation.

• OIG: OIG audits and evaluations have examined home health billing and payment accuracy, and OASIS data are a frequent source of analysis.

Questions to Ask During an OASIS Accuracy Audit

• Did the clinician observe the activity, or rely on report?

• Does the narrative explain the score?

• Do therapy and nursing notes from the same week agree?

• Is the score consistent with the patient's diagnosis and clinical picture?

• Was the response changed after review, and if so, by whom and why?

A Hypothetical Example

An agency's internal data shows that 70 percent of its periods are in the high functional impairment level, compared with a much lower share among peers. An internal audit of 50 start of care assessments finds that one team frequently scores lower body dressing and bathing as requiring maximal assistance, while visit notes describe patients dressing and bathing with only setup or standby help. Recalculating the functional points moves 14 periods from high to medium impairment.

Working with counsel, the agency expands the review to estimate the overpayment for the affected period, reports and returns it, retrains the team, revises its OASIS review process to require clinician-documented support for any change, and begins monthly monitoring. Six months later, its functional level distribution is much closer to peers, and audit results show improved accuracy.

Key Takeaways

• The PDGM functional impairment level comes from a small set of OASIS items, so accuracy on those items directly affects payment.

• Score what the patient can safely do on the day of assessment, following the OASIS Guidance Manual.

• Support every response with observations in the narrative and consistent notes across disciplines.

• Design OASIS review processes that correct errors in both directions and leave final scoring to the assessing clinician.

• Monitor functional level distributions against peers and investigate outliers.

• Audit regularly and address any overpayments promptly under the 60-day rule.

• Keep financial goals separate from clinical assessment.

Frequently Asked Questions

Which OASIS items affect PDGM payment?

The functional impairment level is based on M1800, M1810, M1820, M1830, M1840, M1850, M1860, and M1033. CMS updates the points and thresholds annually.

Do diagnoses on OASIS determine the clinical group?

Under PDGM, the clinical group and comorbidity adjustment are based on diagnoses reported on the claim, which should be consistent with the medical record.

Can a reviewer change the payment group?

Yes. If the medical record does not support the OASIS responses, a reviewer may adjust the HIPPS code, resulting in an overpayment or underpayment.

Is it acceptable for OASIS reviewers to change scores?

Changes should be made by the assessing clinician, based on his or her observations, following OASIS guidance and with documentation. Processes that systematically increase scores without clinical support create compliance risk.

What should we do if an audit finds overstated scores?

Correct the root causes, retrain clinicians, and evaluate obligations under the 60-day overpayment rule.

Conclusion

Under PDGM, OASIS functional scoring directly affects payment. Accurate scoring supports appropriate payment and quality data, while overstated scoring creates overpayments and legal risk. By understanding which items drive the functional level, training clinicians on OASIS conventions, comparing OASIS responses with the full clinical record, monitoring data patterns, designing review processes that improve accuracy rather than inflate scores, and addressing overpayments promptly, home health agencies can protect themselves in audits and make sure their payments reflect their patients' real needs.

How HealthBridge Can Help

HealthBridge is a healthcare management consulting firm that helps home health agencies improve OASIS accuracy through clinician training, OASIS accuracy audits, functional level analysis, review process design, data monitoring, and corrective action planning. If you want to make sure your OASIS scoring will stand up to audit, please get in touch with us. We will be happy to help you with this topic.

References

• Centers for Medicare & Medicaid Services. OASIS Data Sets and OASIS Guidance Manual. https://www.cms.gov/medicare/quality/home-health/oasis-data-sets

• Centers for Medicare & Medicaid Services. Home Health Patient-Driven Groupings Model. https://www.cms.gov/medicare/payment/prospective-payment-systems/home-health/home-health-patient-driven-groupings-model

• Centers for Medicare & Medicaid Services. Calendar Year (CY) 2026 Home Health Prospective Payment System Final Rule (CMS-1828-F) Fact Sheet. https://www.cms.gov/newsroom/fact-sheets/calendar-year-cy-2026-home-health-prospective-payment-system-final-rule-cms-1828-f

• U.S. Government Publishing Office. Federal Register, Medicare and Medicaid Programs; Calendar Year 2026 Home Health Prospective Payment System Rate Update (December 2, 2025). https://www.govinfo.gov/content/pkg/FR-2025-12-02/html/2025-21767.htm

• Centers for Medicare & Medicaid Services. CY 2027 Home Health Prospective Payment System Regulations and Notices. https://www.cms.gov/medicare/payment/prospective-payment-systems/home-health/home-health-prospective-payment-system-regulations-and-notices/cms-1844-p

• Centers for Medicare & Medicaid Services. Medicare Program Integrity Manual, Chapter 8, Section 8.4, Statistical Sampling for Overpayment Estimation. https://www.cms.gov/regulations-and-guidance/guidance/manuals/downloads/pim83c08.pdf

• Electronic Code of Federal Regulations. 42 CFR 484.55, Condition of Participation: Comprehensive Assessment of Patients. https://www.ecfr.gov/current/title-42/chapter-IV/subchapter-G/part-484/subpart-B/section-484.55

• Electronic Code of Federal Regulations. 42 CFR 484.45, Condition of Participation: Reporting OASIS Information. https://www.ecfr.gov/current/title-42/chapter-IV/subchapter-G/part-484/subpart-B/section-484.45

• Electronic Code of Federal Regulations. 42 CFR 401.305, Requirements for Reporting and Returning of Overpayments. https://www.ecfr.gov/current/title-42/chapter-IV/subchapter-A/part-401/subpart-D/section-401.305

• U.S. Department of Health and Human Services, Office of Inspector General. General Compliance Program Guidance. https://oig.hhs.gov/compliance/general-compliance-program-guidance/

• U.S. Social Security Administration. Social Security Act, Section 1895, Prospective Payment for Home Health Services. https://www.ssa.gov/OP_Home/ssact/title18/1895.htm