What Is ASC-21? Key Requirements for ASCs

ASC-21 is a patient-reported outcome measure under the CMS Ambulatory Surgical Center Quality Reporting (ASCQR) Program that evaluates improvement following elective primary total hip arthroplasty (THA) and total knee arthroplasty (TKA) using information reported directly by patients before and after surgery.

The measure's full name is the Risk-Standardized Patient-Reported Outcome-Based Performance Measure Following Elective Primary Total Hip Arthroplasty and/or Total Knee Arthroplasty in the ASC Setting (THA/TKA PRO-PM). CMS adapted the THA/TKA PRO-PM for use in ASCs as part of its expansion of patient-reported outcome measurement beyond the hospital inpatient setting.

What does the measure evaluate?

Patients complete a joint-specific survey before surgery and again after recovery: the HOOS JR (Hip Disability and Osteoarthritis Outcome Score for Joint Replacement) for hip patients, and the KOOS JR (Knee Injury and Osteoarthritis Outcome Score for Joint Replacement) for knee patients.

A patient counts as improved if their score rises by at least 22 points on the HOOS JR or 20 points on the KOOS JR. This is the threshold for what the measure defines as substantial clinical benefit.

The facility's result is a risk-standardized improvement rate: the proportion of its patients who reach the substantial clinical benefit threshold, adjusted for differences in patient characteristics so that facilities with more complex patients are not disadvantaged.

Which patients are included?

The measure applies to Medicare fee-for-service beneficiaries age 65 or older who meet the measure's eligibility criteria, including continuous enrollment in Medicare Parts A and B for the 12 months before the procedure and during the procedure.

Because the measure is limited to eligible elective primary THA and TKA procedures, revisions and procedures associated with certain conditions, including fracture, malignancy or infection, fall outside the eligible cohort. Other exclusions include staged procedures during the measurement period and patients who die within 300 days of the procedure.

CMS does not establish a minimum case-volume threshold for the ASC reporting requirement. Instead, compliance during mandatory reporting is based on submitting complete matched data for at least 45 percent of eligible procedures.

What data do ASCs need to collect?

Each eligible patient completes the HOOS JR or KOOS JR twice: once within 90 days before surgery, and again between 300 and 425 days after surgery. Facilities also submit additional data elements for each patient, including risk variables used to adjust for differences in patient characteristics.

Before surgery (within 90 days prior to the procedure):

• HOOS JR or KOOS JR
• Mental health subscale items from either the PROMIS-Global or the VR-12
• The Single Item Literacy Screener (SILS2)
• Additional risk variables, including pain in other lower-extremity joints, back pain, height and weight, and chronic narcotic use (90 days or longer)

After surgery (300 to 425 days after the procedure):

• HOOS JR or KOOS JR

Submissions also include patient and procedure identifiers so CMS can match each patient's preoperative and postoperative surveys. To count toward the reporting completeness requirement during mandatory reporting, an eligible procedure must have complete preoperative data matched with complete eligible postoperative data. Data are submitted through CMS's Hospital Quality Reporting (HQR) system, the same system ASCs use for other ASCQR submissions.

When does reporting become mandatory for ASCs?

CMS adopted the measure into the ASCQR Program in the CY 2024 OPPS/ASC final rule. Voluntary reporting runs from the CY 2025 through CY 2027 reporting periods, and mandatory reporting begins with the CY 2028 reporting period. Performance in that first mandatory period affects the CY 2031 payment determination. Because the pre-operative survey can be collected up to 90 days before surgery, data collection for patients having surgery in early 2028 will begin in the fall of 2027.

CMS has published ASC collection and submission dates for the first two voluntary periods:

What happens if an ASC does not meet the requirements?

Once reporting is mandatory, ASCs must submit complete preoperative data matched with complete postoperative data for at least 45 percent of eligible procedures. The ASCQR Program is a pay-for-reporting program. ASCs that do not meet its requirements receive a 2.0 percentage point reduction to their annual Medicare payment update for the applicable year.

The payment consequence is tied to reporting, not to how well patients improve. Importantly, the 45 percent reporting threshold should not be confused with the clinical improvement thresholds. The 22-point HOOS JR and 20-point KOOS JR thresholds are used to determine whether an individual patient achieved substantial clinical benefit and to calculate the facility's risk-standardized improvement rate. They are not minimum performance scores an ASC must achieve to avoid the ASCQR payment reduction. ASCQR Program data are publicly reported through CMS's Care Compare, with facilities provided an opportunity to preview applicable results before public release.

How can ASCs prepare?

The central challenge is the long interval between surgery and the post-operative survey. A center preparing for 2028 needs a reliable way to collect pre-operative surveys before surgery, track each patient's post-operative window individually, and follow up with patients who have not responded. Those processes typically involve the surgery center, the surgeon's practice, and whatever technology the center uses to reach patients.

The CY 2025 through CY 2027 voluntary reporting periods give ASCs an opportunity to build and test that process without a payment reduction for choosing not to submit ASC-21 data. Centers can use the voluntary period to evaluate their workflow, identify gaps in patient follow-up, and understand their actual completion rate before reporting becomes mandatory.

Because successful reporting depends on obtaining both complete preoperative and postoperative data within defined collection windows, ASCs may benefit from establishing these workflows well before the first mandatory procedures are performed in 2028.

Working with an experienced ASC management partner can help centers navigate these evolving requirements while integrating them into day-to-day operations. NueHealth works alongside ASCs to strengthen the clinical, operational, and reporting infrastructure needed to adapt to changing quality requirements and support long-term performance.