Diagnostic accuracy of calculated serum osmolarity to predict dehydration in older people: adding value to pathology lab reports

Hooper, Lee ORCID: https://orcid.org/0000-0002-7904-3331, Abdelhamid, Asmaa, Ali, Adam, Bunn, Diane, Jennings, Amy, John, Garry, Kerry, Susan, Lindner, Gregor, Pfortmueller, Carmen, Sjöstrand, Fredrik, Walsh, Neil, Fairweather-Tait, Susan ORCID: https://orcid.org/0000-0002-1413-5569, Potter, John, Hunter, Paul ORCID: https://orcid.org/0000-0002-5608-6144 and Shepstone, Lee (2015) Diagnostic accuracy of calculated serum osmolarity to predict dehydration in older people: adding value to pathology lab reports. BMJ Open, 5 (10). ISSN 2044-6055

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Abstract

Objectives: To assess which osmolarity equation best predicts directly measured serum/plasma osmolality and whether its use could add value to routine blood test results through screening for dehydration in older people.   Design: Diagnostic accuracy study.   Participants: Older people (≥65 years) in 5 cohorts: Dietary Strategies for Healthy Ageing in Europe (NU-AGE, living in the community), Dehydration Recognition In our Elders (DRIE, living in residential care), Fortes (admitted to acute medical care), Sjöstrand (emergency room) or Pfortmueller cohorts (hospitalised with liver cirrhosis).   Reference standard for hydration status: Directly measured serum/plasma osmolality: current dehydration (serum osmolality >300mOsm/kg), impending/current dehydration (≥295mOsm/kg).   Index tests: 39 osmolarity equations calculated using serum indices from the same blood draw as directly measured osmolality.   Results: Across five cohorts 595 older people were included, of whom 19% were dehydrated (directly measured osmolality >300mOsm/kg). Of 39 osmolarity equations, five showed reasonable agreement with directly measured osmolality and three had good predictive accuracy in subgroups with diabetes and poor renal function. Two equations were characterized by narrower limits of agreement, low levels of differential bias and good diagnostic accuracy in ROC plots (areas under the curve >0.8). The best equation was osmolarity =1.86 × (Na+ + K+) + 1.15 × glucose + urea + 14 (all measured in mmol/L). It appeared useful in people aged ≥65 years with and without diabetes, poor renal function, dehydration, in men and women, with a range of ages, health, cognitive and functional status.   Conclusions: Some commonly used osmolarity equations work poorly, and should not be used. Given costs and prevalence of dehydration in older people we suggest use of the best formula by pathology laboratories using a cutpoint of 295mOsm/L (sensitivity 85%, specificity 59%), to report dehydration risk opportunistically when serum glucose, urea and electrolytes are measured for other reasons in older adults.

Item Type: Article
Uncontrolled Keywords: dehydration,older adults,aged,osmolality,osmolarity,diagnostic accuracy,screening,sdg 3 - good health and well-being ,/dk/atira/pure/sustainabledevelopmentgoals/good_health_and_well_being
Faculty \ School: Faculty of Medicine and Health Sciences > Norwich Medical School
UEA Research Groups: Faculty of Medicine and Health Sciences > Research Groups > Epidemiology and Public Health
Faculty of Medicine and Health Sciences > Research Groups > Norwich Clinical Trials Unit
Faculty of Medicine and Health Sciences > Research Groups > Health Services and Primary Care
Faculty of Medicine and Health Sciences > Research Groups > Musculoskeletal Medicine
Faculty of Medicine and Health Sciences > Research Groups > Public Health and Health Services Research (former - to 2023)
Faculty of Medicine and Health Sciences > Research Groups > Cardiovascular and Metabolic Health
Faculty of Medicine and Health Sciences > Research Groups > Nutrition and Preventive Medicine
Faculty of Medicine and Health Sciences > Research Groups > Health Promotion
Faculty of Science > Research Groups > Norwich Epidemiology Centre
Faculty of Medicine and Health Sciences > Research Groups > Norwich Epidemiology Centre
Faculty of Social Sciences > Research Centres > Water Security Research Centre
Faculty of Medicine and Health Sciences > Research Centres > Population Health
Faculty of Medicine and Health Sciences > Research Centres > Lifespan Health
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Depositing User: Pure Connector
Date Deposited: 22 Oct 2015 12:00
Last Modified: 19 Oct 2023 01:29
URI: https://ueaeprints.uea.ac.uk/id/eprint/54749
DOI: 10.1136/bmjopen-2015-008846

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