National trends in cerebrospinal fluid biomarker testing for Alzheimer's disease in Japan.

BACKGROUND: Although the usefulness of cerebrospinal fluid (CSF) biomarkers for Alzheimer's disease (AD) is well-known, their use differs widely between countries. In Japan, phospho-tau181 (p-tau181) testing for determining the cause of dementia has been covered by national health insurance since 2012 and amyloid-β (Aβ)42/40 ratio for evaluating eligibility for anti-Aβ antibodies has been covered since 2023. However, safety concerns and burdens limit their use. OBJECTIVE: Here, we report national trends in CSF biomarker testing for AD in Japan. METHODS: We used open datasets from the national database covering nearly all health insurance claims in Japan from 2014 to 2023. RESULTS: The annual number of health insurance claims for p-tau181 testing gradually increased from 1358 (2014) to 3420 (2023); 79-86% of claims were from inpatient settings throughout the study period. The number of claims was highest in the 75-79 age group and higher in women in older age. Regional variances were identified. The number of claims for CSF Aβ42/40 ratio testing in its first 3 months (December 2023 to March 2024) was 729; 56% of claims were from outpatient settings. CONCLUSIONS: Although the number of health insurance claims for CSF p-tau181 testing has gradually increased, this number is low compared with the previously estimated annual diagnosis of AD. Tests are often performed in inpatient settings and regional inequity exists, whereas CSF Aβ42/40 ratio testing is slightly more often performed in outpatient settings. These data are important for understanding the current situation before the implementation of biomarker-based AD diagnosis in Japan.