Cognitive impairment is common in elderly populations but remains underdiagnosed.

We sought to derive contemporary population-level diagnosis rates of mild cognitive impairment (MCI) and dementia from US Medicare data and compare those rates to expected rates based on a predictive model.

We analyzed data from 2017-2019 100% samples for Medicare fee-for-service and Medicare Advantage; diagnoses were identified based on ICD-10 codes. To estimate the expected prevalence of MCI and dementia, we used the Health and Retirement Study, a nationally representative, longitudinal survey of older US adults, which includes formal cognitive assessments. We predicted MCI, dementia, and any cognitive impairment based on age, sex, race/ethnicity, dual eligibility status (ie, individuals covered by both Medicare and Medicaid), and a continuous linear trend to account for the secular decline in dementia incidence with a probit model. The model was calibrated using 2000-2014 data, validated using 2016 data, and applied to 2017-2019 Medicare data to generate expected diagnosis rates.

Dementia is diagnosed in the US Medicare population at approximately the expected rate; however, MCI remains substantially underdiagnosed. If failure to diagnose is not addressed, it will have negative implications for timely access to a disease-modifying treatment for Alzheimer’s disease.