Plasma glucose does not influence performance on standard cognitive screening tests in a mixed memory clinic cohort

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AbstractBackgroundIt has been shown under experimental conditions that cognitive performance, especially working memory, is impaired in type I and type II diabetes during hyperglycemic and hypoglycemic conditions, perhaps due to altered cerebral glucose metabolism. It is not known if patients with neurodegenerative diseases, who also exhibit pathological cerebral glucose metabolism, are affected in a similar manner by their intrinsic plasma glucose levels. We aimed to test if performance on two standard cognitive screening tests is influenced by intrinsic plasma glucose levels in a memory clinic cohort.MethodIn this retrospective study, we included patients from the Copenhagen Memory Clinic Cohort (CMCC) with an available Mini Mental‐State Examination (MMSE) test score and a plasma glucose measurement performed in conjunction with cognitive testing. Patients were included from the inception of the cohort in 2008 till September 2021. We built linear regression models with MMSE and Addenbrooke’s Cognitive Examination (ACE) test scores as the outcome and plasma glucose as the explaining variable and adjusted models for age, sex and diabetes (plasma glucose measurement > 11.1 mmol/L). We explored non‐linear relationships by adding squared terms to the models and by fitting cubic spline regression models.ResultIn total, 2714 patients had an available MMSE score and a plasma glucose measurement. Patients had a mean age of 71.6 years [range 19‐99] and a baseline plasma glucose level of 5.8 mmol/L [range 2.7‐28.1]. A total of 581 of patients had a plasma glucose level outside normal range (<4.2 or >6.3 mmol/L). A total of 31.2% of the cohort studied had a diagnosis of Alzheimer’s disease (AD). MMSE and ACE total scores were not influenced by plasma glucose in a linear nor in a non‐linear fashion, when we adjusted for age, sex and diabetes. Sub‐group analyses in patients with AD and in patients with cerebrovascular disease showed similar results.ConclusionPlasma glucose levels inside normal range were not shown to influence performance on routinely applied cognitive tests and do not need be taken into consideration when interpreting test results from memory clinic patients.