%X OBJECTIVES: To assess plasma phosphorylated tau181 (p-tau181) levels in Alzheimer's disease (AD), cognitively impaired non-AD participants (CI non-AD) and Control participants in the Alzheimer's Disease Neuroimaging Initiative (ADNI) dataset that could potentially act as reference data for clinic diagnoses of AD. METHODS: Data from 1558 participants (649 AD participants, 445 CI non-AD participants and 464 controls) were examined, comparing p-tau181 levels between Controls, AD and other dementias, stratified by age. RESULTS: There were significant differences in plasma p-tau181 values between Controls and those with AD at all ages up to 85Â years. There were also significant differences between AD and CI non-AD participants up to the age of 85Â years. CONCLUSIONS: Plasma P-tau181 may be a useful tool in the diagnosis of AD in those clinical settings where biomarkers have traditionally been less used. P-tau181 may be less useful as an aid to diagnosis in the very oldest-old. Further work is needed to establish the feasibility and utility of this biomarker within dementia diagnosis services not led by Neurologists, such as UK National Health Service Memory Services. %C England %I John Wiley and Sons %K Alzheimer's disease, biomarker, diagnosis, p-tau181 %L discovery10143524 %T Practical application of Alzheimer's Disease Neuroimaging Initiative plasma P-tau181 reference data to support diagnosis of Alzheimer's disease %N 2 %D 2022 %O This version is the author accepted manuscript. For information on re-use, please refer to the publisher's terms and conditions. %A Jemma Hazan %A Duncan Alston %A Nick C Fox %A Robert Howard %V 37 %J International Journal of Geriatric Psychiatry