About 1 in 9 older adults over 65 has Alzheimer's disease (AD), many of whom also have multiple other chronic conditions such as hypertension and diabetes, necessitating careful monitoring through laboratory tests. Understanding the patterns of laboratory tests in this population aids our understanding and management of these chronic conditions along with AD. In this study, we used an unimodal cosinor model to assess the seasonality of lab tests using electronic health record (EHR) data from 34,303 AD patients from the OneFlorida+ Clinical Research Consortium. We observed significant seasonal fluctuations higher in winter in lab tests such as glucose, neutrophils per 100 white blood cells (WBC), and WBC. Notably, certain leukocyte types like eosinophils, lymphocytes, and monocytes are elevated during summer, likely reflecting seasonal respiratory diseases and allergens. Seasonality is more pronounced in older patients and varies by gender. Our findings suggest that recognizing these patterns and adjusting reference intervals for seasonality would allow healthcare providers to enhance diagnostic precision, tailor care, and potentially improve patient outcomes.

The authors have declared no competing interest.

This project was partially supported by Florida State University Institute for Successful Longevity, the Agency for Healthcare Research and Quality under award number 1R21HS29969, the National Institute on Aging under award number R21AG061431, and the University of Florida- Florida State University Clinical and Translational Science, which is supported in part by the NIH National Center for Advancing Translational Sciences under award number UL1TR001427. VM and SB were supported by the Novo Nordisk Foundation (grants NNF17OC0027594 and NNF14CC0001).

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Florida State University and University of Florida Institutional Review Boards approved this study.

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I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

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I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

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The data used in this study cannot be shared due to the privacy concern of the electronic health records.