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

Prado, Carla M.; Siervo, Mario; Bunn, Diane; Prado, Carla M; Hooper, Lee

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 = 1.8 × 3 (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 (

Citation

Prado, C. M., Siervo, M., Bunn, D., Prado, C. M., & Hooper, L. (2014). Accuracy of prediction equations for serum osmolarity in frail older people with and without diabetes. American Journal of Clinical Nutrition, 100(3), 867-876. https://doi.org/10.3945/ajcn.114.086769

• Journal Article Type: Article
• Acceptance Date: Jun 3, 2014
• Online Publication Date: Jul 16, 2014
• Publication Date: Sep 1, 2014
• Deposit Date: Nov 20, 2019
• Journal: American Journal of Clinical Nutrition
• Print ISSN: 0002-9165
• Electronic ISSN: 1938-3207
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 100
• Issue: 3
• Pages: 867-876
• DOI: https://doi.org/10.3945/ajcn.114.086769
• Keywords: Nutrition and Dietetics; Medicine (miscellaneous)
• Public URL: https://nottingham-repository.worktribe.com/output/3345016