Table 2.
Water-induced reduction of copeptin and habitual blood and urine parameters (at the end of control week) in water-responders and non-water-responders
| Non-water-respondersa (n = 25) | Water-respondersb (n = 12) | p value | ||
|---|---|---|---|---|
| Reduction in plasma copeptin concentration (after 1 week of extra water as compared to after control week) | ||||
| P-copeptin reduction (pmol/L) | 0.24 (− 0.21–0.69)c | 3.26 (2.71–3.80)c | < 0.001 | |
| P-copeptin reduction (% of habitual copeptin concentration) | 2.7 (− 8.3–13.7)c | 41.2 (33.8–48.6)c | < 0.001 | |
| Habitual urine and plasma concentrations (at the end of control week) | ||||
| P-copeptin (pmol/L) | 3.64 (3.22–5.52) | 7.46 (6.02–9.53) | < 0.001 | |
| U-osmolality (mosm/kg H2O) | 455.0 (316.5–562.5) | 664.0 (473.5–962.8) | 0.008 | |
| U-volume (mL/24 h) | 1411 (1280–2194) | 1036 (768–1357) | 0.005 | |
| Osmolar excretion rate (mosm/24 h) | 714 (544–789) | 635 (482–1001) | 0.44 | |
| P-osmolality (mosm/kg H2O) | 293.0 (290.0–296.5) | 295.0 (293.5–301.5) | 0.04 | |
| P-urea (mmol/L)d | 4.53 (0.94) | 5.19 (1.44) | 0.18e | |
| P-sodium (mmol/L)d | 140.1 (1.52) | 141.4 (1.58) | 0.03e | |
| P-potassium (mmol/L)d | 3.81 (0.18) | 3.85 (0.18) | 0.52e | |
| P-creatinine (µmol/L) | 71.0 (65.0–83.0) | 79.5 (66.0–87.0) | 0.79 | |
Data are expressed as median (interquartile range) if nothing else is specified
Fasting values if nothing else is specified
aNon-water responder refers to subjects with the lowest water-induced copeptin reduction, i.e., first and second tertile of Δ-copeptin (corresponding to a copeptin reduction of ≤ 2 pmol/L)
bWater responder refers to subjects with the highest water-induced copeptin reduction, i.e., third tertile of Δ-copeptin (corresponding to a copeptin reduction of > 2 pmol/L)
cData are expressed as mean (95 CI)
dData are expressed as mean (SD)
eIndependent sample T test