Individuality and responsiveness of biochemical indices of dehydration in hospitalized elderly patients

Abstract

Background: dehydration is common in elderly patients, but difficult to detect, by either an initial assessment of fluid balance or by monitoring fluid balance over time. In clinical chemistry, population-based reference ranges arc only of value for monitoring individual patients if within-subject variability in serial test results over time is larger than between-subject variability. This may have important implications in monitoring fluid balance. Ainu to assess the within-and between-subject variability of serial laboratory test results in euvolaemia and their responsiveness to dehydration in elderly patients. Methods: over 16 months, 218 patients were admitted to the geriatric department and 53 consented to participate. Fluid balance was assessed twice a week by physical examination, laboratory tests and weighing. Changes in fluid balance were quantified by measuring total body and extracellular water applying deuterium-and bromide-dilution techniques. Within-and between-subject variability in euvolaemia and responsiveness indexes (RI) for dehydration were calculated for haematocrit, serum sodium, urea and creatinine concentrations and for the urea/creatinine ratio. Results: during hospitalization 14 patients suffered from dehydration and 27 remained euvolaemic. Data from 12 overhydrated patients were excluded. In a mean study period of 30 days, each patient's fluid balance was assessed 6.3 (1.9) times. This resulted in 1084 laboratory tests and 271 assessments of fluid balance. In all quantities withinsubject variability was much smaller than between-subject variability in euvolaemia. Responsiveness of creatinine (mean RI = 2.5) was best and similar to the RI of serial weights (mean RI = 2.9). Conclusion: population-based reference ranges are of limited value in monitoring fluid balance. Repeatedly measuring plasma creatinine, combined with physical examination and weighing is the best way to monitor fluid balance in elderly patients.

Dehydration among Long-Term Care Elderly Patients with Oropharyngeal Dysphagia

“…Thus, if the results of this study were interpolated to a wider system, the hydration status of LTC residents is much in want. Previous studies [4,26] report a 26-39% prevalence of dehydration in elderly LTC residents. However, unlike our study, they do not mention the swallowing condition of their patients.…”

“…The commonly used biochemical indices of dehydration were derived from population-based reference ranges (PBRRs), determined in a non-aged population, and they show clinically relevant changes with increasing age [26,27] . Thus these indices are insufficiently reliable in the geriatric population.…”

“…On the other hand, laboratory parameters of dehydration are stable over time within geriatric subjects thus permitting the construction of within-subject coefficients of variation, i.e. subject-specific reference ranges (SSRRs) [26] . Hence, in cases where repeated measurements are available, dehydration can be best diagnosed and fluid balance monitored over time by applying the above-mentioned SSRRs (instead of the similar analysis by intuition, performed by many physicians, when judging serial laboratory results).…”

Laboratory results in the elderly: the Sydney Older Persons Study

“…The reference intervals are usually derived statistically from populations of healthy individuals (typically younger and independently mobile), raising the issue of their appropriateness to sick, older people. 1,2 Usual laboratory reference intervals are constructed in a way that de¢nes 5% of people who are normal as lying outside the reference interval. Parametric methods based on two standard deviations of the mean and non-parametric methods are used in their de¢ni-tion.…”

Heat waves and dehydration in the elderly

“…Serum creatinine is the most sensitive laboratory measure, although body weight is most responsive to changes in hydration. 10 By itself, dehydration is an important indicator of neglect.…”