(145) Unraveling the use of diagnostic tests for mild cognitive impairment, Alzheimer’s disease, and other dementias: a real-world study

Background: Use of neuroimaging [e.g. magnetic resonance imaging (MRI), positron emission tomography (PET), or computed tomography (CT) scan], cerebrospinal fluid (CSF), and blood biomarker tests can contribute to a more accurate and earlier diagnosis of Alzheimer’s disease (AD). However, little is known how these tests are used in the real world.

Objectives: To understand the use of existing diagnostic tests, particularly in combinations, for mild cognitive impairment (MCI), AD, or other dementias in a large US population

Methods: We performed a retrospective observational study design using data from the Medicare 100% Research Identifiable files and included Medicare fee-for-service beneficiaries ≥ 67 years old and newly diagnosed with MCI, AD, or other dementias between 2015 and 2020. The study index date was the first disease diagnosis date. We reported the test rates to understand the use of MRI, CT, PET, CSF, and any blood tests, particularly in combinations, within 1 year before the index date. Among patients who received a test, we reported the mean [standard deviation (SD)] number of tests used per patient.

Results: The final study sample consisted of 653,420 patients (9.1% MCI, 30.3% AD, and 60.6% other dementias). During the 1 year before the index date, 71.9% had at least one blood test, 53.9% had any neuroimaging test, 46.4% had CT, 17.7% had MRI, 0.7% had PET, and 2.2% had CSF. For test combinations, 39.9% received blood + imaging tests, 1.5% had blood + CSF +imaging tests, 0.41% had blood+ CSF tests, and 0.23% had CSF +imaging tests. When examined in a chronological order, the most common combination of tests is a blood test first followed by an imaging test (15.3%). Excluding blood tests, CT + MRI is the most common combination without chronological order (9.5%). CT followed by MRI is the most common combination in chronological order (3.2%). Among patients who received a test, on average, patients received 2.1 (1.4) blood tests, 1.8 (1.4) any imaging tests [1.7 (1.3) for CT, 1.2 (0.6) for MRI, 1 (0.1) for PET], and 1.3 (1.1) CSF tests.

Conclusions: During the six years preceding the arrival of disease-modifying therapies, blood tests, MRI and CT were the predominant diagnostic tests, while the use of CSF and PET was very infrequent. Patients often received a combination of or repeated diagnostic tests. The current study sheds light on the diagnostic testing patterns for patients with MCI, AD, or other dementias in the real-word setting. Future research is needed to understand the reasons for patients undergoing multiple testing in order to optimize the timing to definite diagnosis.