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Background: Most patients receive a diagnosis of dementia late in the course of the disease. In an effort to learn more about the potential for earlier detection, we examined comorbidity burden preceding a diagnosis of dementia in a cohort of older adults.Methods: Cognitive status of ARIC Study cohort participants (n=6,538) was adjudicated at Visit 5 (2011-2013) by a classification committee of physicians and neuropsychologists using a battery of neurocognitive tests, functional assessments, and neurologic exam. Additionally, cognitive status of participants who did not attend the Visit 5 examination, but were alive at the time of the visit (n= 2,289) was ascertained through a Telephone Interview for Cognitive Status-Modified (TICS) or Clinical Dementia Rating (CDR) informant interview. We examined the presence of dementia diagnostic codes in claims for inpatient and outpatient services occurring during the years 1991-2013 and preceding dementia diagnoses among all ARIC cohort participants with a dementia classification. In a sample of study participants who were enrolled in continuous fee-for-service (FFS) Medicare for at least 5 years prior to dementia ascertainment, we examined the comorbidity profile preceding the date of dementia ascertainment using ICD9 diagnostic codes obtained from inpatient records and claims for outpatient office visits.Results: Of the 7,283 ARIC participants enrolled in FFS Medicare at the time of ARIC dementia ascertainment (39.6% men, 26.4% black, mean age 76.7 years (SD 5.4)), 901 (12.4%) were classified as having dementia. Only 41.3% of those classified with dementia and 2.6% of those classified as cognitively intact had dementia diagnostic codes in any position in claims for inpatient or outpatient care preceding the ascertainment of cognitive status. In analyses limited to participants with 5 years of continuous FFS Medicare enrollment prior to the cognitive status ascertainment, we observed a consistently greater frequency of hospitalizations among study participants with a subsequent dementia classification, as compared to those with no cognitive impairment (1.62 (SD 0.08) vs. 1.10 (SD 0.05) hospitalizations per participant in the year preceding dementia diagnosis, respectively). No difference in the frequency of outpatient visits was observed. In addition to a greater frequency of diagnostic codes for cerebrovascular disease and cerebral degeneration, those with a positive dementia classification had a greater prior frequency of ICD9 codes for depression, heart failure, acute renal failure, and fluid and electrolyte disorders, as compared to those with no cognitive impairment.Conclusion: Dementia patients may have distinct comorbidity profiles in the years preceding a diagnosis. A greater understanding of these profiles is important for characterizing patient factors that may enable early detection and management.