Human Hydration Status Monitoring
Condition: Dehydration
MeSH terms: Dehydration
Study type: Interventional

Summary: 
      The sports medicine literature provides a consensus on what threshold values constitute
      euhydration (normal body water) using a variety of hydration assessment markers (e.g., blood,
      urine). The investigators add to this literature by providing decision levels for multiple
      body fluids which can be used as starting points for diagnosing and treating dehydration. At
      present, plasma osmolality (Posm) provides the best potential measure for static dehydration
      assessment (spot measure), while dynamic dehydration assessment (serial monitoring) is best
      accomplished using change values for Posm, urine specific gravity, or body mass (weight).
      These findings should be considered useful for clinical, military, and sports medicine
      communities.
    

Detailed description: 
      Well-recognized markers for static (one time) or dynamic (monitoring over time) dehydration
      assessment have not been rigorously tested for their usefulness in clinical, military, and
      sports medicine communities.

      This study evaluated the components of biological variation and accuracy of potential markers
      in plasma, urine, saliva, and body mass, for static and dynamic dehydration assessment.
      Design: Eighteen healthy volunteers (13M, 5F) were studied while carefully controlling
      hydration and numerous pre-analytical factors. Biological variation was determined over three
      consecutive days using published methods. Atypical values based on statistical deviations
      from a homeostatic set-point were examined. Measured deviations in body fluid were produced
      using a separate, prospective dehydration experiment and evaluated by ROC analysis to
      quantify diagnostic accuracy.

      All dehydration markers displayed substantial individuality and half displayed marked
      heterogeneity of intra-individual variation. Decision levels for all dehydration markers were
      within one standard deviation of the ROC criterion values and most were nearly identical to
      the prospective group means after dehydrating volunteers by 1.8 - 7.0% of body mass. However,
      only plasma osmolality (Posm) showed statistical promise for use in static dehydration
      assessment. A 301 ± 5 mmol/kg diagnostic decision level is proposed. Reference change values
      (RCV) of 9 mmol/kg (Posm), 0.010 (urine specific gravity, Usg), and 2.5% change in body mass
      (Bm) were also statistically valid for dynamic dehydration assessment at the 95% probability
      level.

      Posm is the only useful marker for static dehydration assessment. Posm, Usg, and Bm are valid
      markers in the setting of dynamic dehydration assessment.
    

Intervention name(s): Dehydration
Intervention type(s): Procedure
Intervention description(s): Subjects were dehydrated by 2 - 7% of body mass over 3-5 hours using exercise-heat stress and fluid restriction.
Other intervention name(s): Hypohydration
Intervention model: Single Group Assignment
Intervention model description: single-sample pre-post design
Masking: Single
Primary purpose: Basic Science
Keywords: dehydration; hypohydration; diagnostic accuracy; biological variation; hydration assessment; body mass; osmolality; plasma; saliva; urine