Biological Variation and Diagnostic Accuracy of Dehydration Assessment Markers
ARMY RESEARCH INST OF ENVIRONMENTAL MEDICINE NATICK MA THERMAL AND MOUNTAIN MEDICINE DIVISION
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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 the accuracy of potential markers in plasma, urine, saliva, and body mass Bm for static and dynamic dehydration assessment. Design We studied 18 healthy volunteers 13 men and 5 women while carefully controlling hydration and numerous preanalytic factors. Biological variation was determined over 3 consecutive days by using published methods. Atypical values based on statistical deviations from a homeostatic set point were examined. Measured deviations in body fluid were produced by using a separate, prospective dehydration experiment and evaluated by receiver operating characteristic ROC analysis to quantify diagnostic accuracy. Results All dehydration markers displayed substantial individuality and one-half of the dehydration markers displayed marked heterogeneity of intraindividual variation. Decision levels for all dehydration markers were within one SD of the ROC criterion values, and most levels were nearly identical to the prospective group means after volunteers were dehydrated by 1.8-7.0 of Bm. However, only plasma osmolality Posm showed statistical promise for use in the static dehydration assessment. A diagnostic decision level of 301 plus or minus 5 mmolkg was proposed. Reference change values of 9 mmolkg Posm, 0.010 urine specific gravity Usg, and 2.5 change in Bm were also statistically valid for dynamic dehydration assessment at the 95 probability level.
- Medicine and Medical Research