Table 1.
Characteristics of methods for assessing hydration
| Hydration assessment/variable | Hydrated upper limit | Limitationsa | Precision/reliability | Cost | Invasiveness | Administrator skill required | Time required |
|---|---|---|---|---|---|---|---|
| Stable isotope dilution | N/A | Expensive and time consuming | 5 | 5 | 5 | 5 | 5 |
| Neutron activation analysis | N/A | Expensive and time consuming | 5 | 5 | 5 | 5 | 5 |
| Haematocrit | < 2% change | Influenced by many confounding factors | 3 | 3 | 3 | 3 | 2 |
| Plasma/serum osmolality | < 296 mmol/kg | Expensive and invasive | 4 | 4 | 4 | 4 | 2 |
| Serum sodium concentration | < 145 mEq/L | Expensive and invasive | 3 | 4 | 4 | 4 | 2 |
| Hormonal variables | N/A | Expensive and undetermined validity/reliability | 2 | 4 | 4 | 5 | 4 |
| Urine specific gravity | < 1.020 SG | Many confounding factors | 2 | 2 | 2 | 2 | 1 |
| Urine osmolality | < 700 mmol/kg | Many confounding factors | 2 | 3 | 2 | 3 | 2 |
| Urine colour | < 4 | Many confounding factors | 1 | 1 | 2 | 1 | 1 |
| Saliva osmolality | < 61 mmol/kg | Questionable reliability | 1 | 3 | 2 | 3 | 2 |
| Tear osmolality | < 310 mmol/kg | Undetermined validity/reliability | 3 | 3 | 2 | 3 | 2 |
| Body mass | < 2% change | Many confounding factors and only works within limited time periods | 4 | 1 | 1 | 1 | 1 |
| Bioimpedance | N/A | Many confounding factors and questionable reliability | 3 | 2 | 1 | 1 | 1 |
| Vital signsa | N/A | Questionably validity/reliability | 1 | 1 | 1 | 2 | 1 |
| Sensation of thirst | < 3 (scale of 1–9) | Low sensitivity | 1 | 1 | 1 | 1 | 1 |
Rating: 1 = lowest, 5 = highest. N/A = Clear cut-off has not been defined or do not apply. aSee the respective section for more details