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Cited by 83Electrolyte and hormonal disordersBody Composition Measurement TechniquesGeriatric Care and Nursing Homes

Accuracy of prediction equations for serum osmolarity in frail older people with and without diabetes , , ,

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Siervo, Mario, Bunn, Diane, Prado, Carla M, Hooper, Lee·2014·The American Journal of Clinical Nutrition
DOI 10.3945/ajcn.114.086769PMC PMC4135495
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Abstract

Background Serum osmolality is an accurate indicator of hydration status in older adults. Glucose, urea, and electrolyte concentrations are used to calculate serum osmolarity, which is an indirect estimate of serum osmolality, but which serum osmolarity equations best predict serum osmolality in the elderly is unclear. Objective We assessed the agreement of measured serum osmolality with calculated serum osmolarity equations in older people. Design Serum osmolality was measured by using freezing point depression in a cross-sectional study. Plasma glucose, urea, and electrolytes were analyzed and entered into 38 serum osmolarity-prediction equations. The Bland-Altman method was used to evaluate the agreement and differential bias between measured osmolality and calculated osmolarity. The sensitivity and specificity of the most-promising equations were examined against serum osmolality (reference standard). Results A total of 186 people living in UK residential care took part in the Dehydration Recognition In our Elders study (66% women; mean ± SD age: 85.8 ± 7.9 y; with a range of cognitive and physical impairments) and were included in analyses. Forty-six percent of participants had impending or current dehydration (serum osmolality ≥295 mmol/kg). Participants with diabetes (n = 33; 18%) had higher glucose (P < 0.001) and serum osmolality (P < 0.01). Of 38 predictive equations used to calculate osmolarity, 4 equations showed reasonable agreement with measured osmolality. One [calculated osmolarity = 1.86 × (Na⁺ + K⁺) + 1.15 × glucose + urea +14; all in mmol/L] was characterized by narrower limits of agreement and the capacity to predict serum osmolality within 2% in >80% of participants, regardless of diabetes or hydration status. The equation's sensitivity (79%) and specificity (89%) for impending dehydration (≥295 mmol/kg) and current dehydration (>300 mmol/kg) (69% and 93%, respectively) were reasonable. Conclusions The assessment of a panel of equations for the prediction of serum osmolarity led to identification of one formula with a greater diagnostic performance. This equation may be used to predict hydration status in frail older people (as a first-stage screening) or to estimate hydration status in population studies. This trial was registered at the Research Register for Social Care (http://www.researchregister.org.uk) as 122273.

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  • 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 [229]

    The Methods evaluate 38 equations, and the Results (Assessment of absolute bias; Bland–Altman analysis) identify only four with the smallest differences from measured osmolality, supporting the concern about most equations’ predictive accuracy. But diagnostic accuracy was assessed only for selected equations, and the Discussion says the findings are specific to frail older people in residential care, not older adults generally. Page numbers are unavailable in our copy. (LLM, conf=0.85)

    Experimental — accuracy not yet measured

  • 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 [229]

    The Discussion reports that the stated equation best predicted measured serum osmolality in frail older people with and without diabetes; the Results include participants with differing hydration status, ages, and cognitive and physical abilities. But the Methods recruited only residential-care residents and excluded people with renal failure. The Discussion says applicability to community-dwelling older people and those with renal failure needs testing; this paper does not establish performance in hospitals either. Page numbers were not supplied in our copy. (LLM, conf=0.91)

    Experimental — accuracy not yet measured

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Cites

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Authors
Siervo, M., Bunn, D., Prado, C. M., & Hooper, L.
Affiliations
University of East Anglia (GB)
ORCID
Venue
The American Journal of Clinical Nutrition
Publisher
Elsevier BV
Published
2014-09
Volume
100
Issue
3
Pages
867-876
ISSN
0002-9165 (ISSN-L)
DOI
10.3945/ajcn.114.086769
PMC
PMC4135495
OpenAlex
W2163411949
Cited by
83
References
5
Citations by year
2026: 2 · 2025: 7 · 2024: 5 · 2023: 11 · 2022: 7 · 2021: 4 · 2020: 9 · 2019: 6 · 2018: 9 · 2017: 4 · 2016: 9 · 2015: 7 · 2014: 3
FWCI
6.15
Type
journal article
Language
en
Open access
Licence
Locations
  • American Journal of Clinical Nutrition (publishedVersion)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
  • Repository@Nottingham (University of Nottingham) (submittedVersion, cc-by)
  • Repository@Nottingham (University of Nottingham) (submittedVersion)
  • UEA Digital Repository (University of East Anglia) (submittedVersion)
  • Newcastle University ePrints (Newcastle Univesity)
Funders
National Institute for Health and Care Research (CDF-2011-04-025)
Topics
  • Health Sciences › Medicine › Pulmonary and Respiratory Medicine › Electrolyte and hormonal disorders
  • Health Sciences › Medicine › Physiology › Body Composition Measurement Techniques
  • Health Sciences › Health Professions › General Health Professions › Geriatric Care and Nursing Homes
Keywords
serum osmolality, dehydration, hydration status, frail elderly, diabetes mellitus, residential care, freezing point depression, plasma glucose, urea, electrolytes, diagnostic accuracy, sensitivity and specificity, Bland-Altman agreement, cognitive impairment, physical impairment
MeSH terms
Aged, Aged, 80 and over, Algorithms, Cross-Sectional Studies, Dehydration, England, Female, Homes for the Aged, Humans, Male, Models, Biological, Nursing Homes, Osmolar Concentration, Sensitivity and Specificity, Cohort Studies, Geriatric Assessment, Body Mass Index, Frail Elderly, Early Diagnosis, Diabetes Complications

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