Performance of Claims-based Alzheimer's Disease and Related Dementias Algorithms in Medicare Advantage and Fee-for-Service Populations.

BACKGROUND: Evidence comparing the performance of claims-based dementia algorithms across Medicare Advantage (MA) and fee-for-service (FFS) populations remains limited. We evaluated the validity of two claims-based algorithms across MA and FFS populations. METHODS: We used nationally representative, linked National Health and Aging Trends Study (NHATS)-Medicare data to identify community-dwelling participants with continuous enrollment in MA or FFS during Round 7 (2017; n = 5,018), Round 9 (2019; n = 4,018), and Round 11 (2021-2022; n = 3,086). Using NHATS probable dementia as reference standard, we validated the Bynum-Standard and Chronic Condition Warehouse (CCW) dementia algorithms across three time points. RESULTS: Overall, both algorithms demonstrated comparable performance in MA and FFS populations, with high specificity (>97.9%) and negative predictive value [NPV] (>92.9%). The Bynum algorithm showed similar sensitivity between MA and FFS in Rounds 7 (30.2% vs. 29.1%) and 11 (25.6% vs. 23.9%), but lower sensitivity in MA for Round 9 (25.0% vs. 36.4%). Positive predictive value [PPV] was similar between MA (62.7%-70.6%) and FFS (62.1%-70.4%) across all rounds. The CCW algorithm demonstrated greater MA-FFS differences, with lower sensitivity in MA for Rounds 9 (30.8% vs. 46.9%) and 11 (35.0% vs. 49.3%) and similar sensitivity for Round 7 (40.4% vs. 42.2%). PPV varied across rounds in both MA and FFS [(Round 7: 76.3% vs. 71.2%) to (Round 11: 68.5% vs. 76.4%)]. Both algorithms identified participants with more severe dementia. CONCLUSION: Claims-based dementia algorithms demonstrate broadly consistent performance in MA and FFS populations, with high specificity and moderate PPV but comparable or lower sensitivity in MA, informing case ascertainment across Medicare plan type.