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Cited by 109Electrolyte and hormonal disordersClinical Laboratory Practices and Quality ControlBody Composition Measurement Techniques

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

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Hooper, Lee, Abdelhamid, Asmaa, Ali, Adam, Bunn, Diane K, Jennings, Amy, John, W Garry, Kerry, Susan, Lindner, Gregor +7 more·2015·BMJ Open
DOI 10.1136/bmjopen-2015-008846PMC PMC4636668
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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 >300 mOsm/kg), impending/current dehydration (≥295 mOsm/kg). Index tests: 39 osmolarity equations calculated using serum indices from the same blood draw as directly measured osmolality. Results: Across 5 cohorts 595 older people were included, of whom 19% were dehydrated (directly measured osmolality >300 mOsm/kg). Of 39 osmolarity equations, 5 showed reasonable agreement with directly measured osmolality and 3 had good predictive accuracy in subgroups with diabetes and poor renal function. Two equations were characterised by narrower limits of agreement, low levels of differential bias and good diagnostic accuracy in receiver operating characteristic 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 295 mOsm/L (sensitivity 85%, specificity 59%), to report dehydration risk opportunistically when serum glucose, urea and electrolytes are measured for other reasons in older adults. Trial registration numbers: DRIE: Research Register for Social Care, 122273; NU-AGE: ClinicalTrials.gov NCT01754012 .

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  • In older adults, renal function is often poor so that renal parameters no longer accurately signal low-intake dehydration.

    “In older adults, renal function is often poor so that renal parameters no longer accurately signal low-intake dehydration (7,225,226).”

    From ESPEN practical guideline: Clinical nutrition and hydration in geriatrics (2022) · cites this paper as [225]

  • One equation (osmolarity = 1.86 × (Na+ + K+) + 1.15 × glucose + urea + 14) usefully predicted serum osmolality in people aged ≥65 years with and without diabetes, poor renal function, dehydration, in men and women, in the community, residential care, and hospital, with a range of ages, health, cognitive and functional status.

    “However, one equation (osmolarity = 1.86 × (Na+ + K+) + 1.15 × glucose + urea + 14 (all measured in mmol/L)) usefully predicted serum osmolality in people aged ≥65 years with and without diabetes, poor renal function, dehydration, in men and women, in the community, residential care, and hospital, with a range of ages, health, cognitive and functional status (225,229).”

    From ESPEN practical guideline: Clinical nutrition and hydration in geriatrics (2022) · cites this paper as [225]

  • Most existing serum osmolarity equations are not diagnostically accurate to calculate serum osmolality in older adults.

    “Work with a set of European cohorts of older adults has suggested that most existing serum osmolarity equations are not diagnostically accurate to calculate serum osmolality in older adults (225,229).”

    From ESPEN practical guideline: Clinical nutrition and hydration in geriatrics (2022) · cites this paper as [225]

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Authors
Hooper, L., Abdelhamid, A., Ali, A., Bunn, D. K., Jennings, A., John, W. G., Kerry, S., Lindner, G., Pfortmueller, C. A., Sjöstrand, F., Walsh, N. P., Fairweather-Tait, S. J., Potter, J. F., Hunter, P. R., & Shepstone, L.
Affiliations
  • University of East Anglia (GB)
  • Norfolk and Norwich University Hospital (GB)
  • University Hospital of Bern (CH)
  • Medical University of Vienna (AT)
  • Stockholm South General Hospital (SE)
  • Bangor University (GB)
  • Norwich Medical School, University of East Anglia, Norwich, UK
Corresponding author
Hooper, Lee
ORCID
Venue
BMJ Open
Publisher
BMJ
Published
2015-10
Volume
5
Issue
10
Pages
e008846
ISSN
2044-6055 (ISSN-L)
DOI
10.1136/bmjopen-2015-008846
PMC
PMC4636668
OpenAlex
W2173353640
Cited by
109
References
7
Citations by year
2026: 13 · 2025: 14 · 2024: 9 · 2023: 14 · 2022: 7 · 2021: 9 · 2020: 13 · 2019: 10 · 2018: 9 · 2017: 2 · 2016: 7 · 2015: 1 · 2012: 1
FWCI
5.02
Type
journal article
Language
en
Open access
Licence
cc-by
Locations
  • BMJ Open (publishedVersion, cc-by)
  • Europe PMC (PubMed Central) (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • UEA Digital Repository (University of East Anglia) (submittedVersion, cc-by)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion)
Funders
  • National Institute for Health and Care Research (CDF-2011-04-025, 266486)
  • European Commission (266486)
  • Karolinska Institutet
  • Stockholms Läns Landsting
Topics
  • Health Sciences › Medicine › Pulmonary and Respiratory Medicine › Electrolyte and hormonal disorders
  • Health Sciences › Medicine › Physiology › Clinical Laboratory Practices and Quality Control
  • Health Sciences › Medicine › Physiology › Body Composition Measurement Techniques
Keywords
dehydration, older adults, serum osmolality, diagnostic accuracy, electrolytes, serum glucose, urea, renal function, diabetes mellitus, liver cirrhosis, residential care, emergency department, hydration assessment, sodium and potassium, opportunistic screening, cost-effectiveness, limits of agreement
MeSH terms
Adult, Aged, Aged, 80 and over, Dehydration, Europe, Female, Humans, Male, Middle Aged, Osmolar Concentration, Prognosis, ROC Curve, Sensitivity and Specificity, Cohort Studies, Multicenter Studies as Topic, Randomized Controlled Trials as Topic

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