Table 2. Diurnal salivary cortisol of the study participants, before (Day 1) and after (Day 2) a low-dose dexamethasone suppression test.
| VLBW (n = 49) Mean a (SD b) | Term (n = 36) Mean a (SD b) | Mean difference c (95% CI) | P d | |
|---|---|---|---|---|
| Diurnal salivary cortisol (nmol/l) day 1 | ||||
| Upon awakening | 7.6 (2.2) | 7.8 (1.7) | -1.4 (-28.9, 37.1) | .94 |
| Peak after awakening | 15.3 (1.7) | 15.8 (1.4) | -2.9 (-22.4, 21.1) | .78 |
| Awakening response e | 2.0 (1.9) | 2.0 (1.9) | -2.9 (29.2, 33.0) | .85 |
| Awakening AUC f | 10.7 (1.7) | 11.4 (1.4) | -4.3 (22.9, 18.9) | .68 |
| Diurnal AUC g | 4.0 (2.2) | 3.4 (1.6) | 18.9 (-14.7, 66.0) | .30 |
| At 22:00 hours, before taking dexamethasone | 1.5 (4.0) | 1.0 (2.2) | 55.6 (-12.1, 74.8) | .13 |
| Diurnal salivary cortisol (nmol/l) day 2 | ||||
| Upon awakening | 0.6 (5.6) | 0.4 (3.2) | 24.5 (-39.5, 55.9) | .55 |
| Peak after awakening | 1.0 (5.3) | 1.1 (3.2) | -13.7 (-56.2, 69.8) | .67 |
| Awakening response e | 1.4 (2.4) | 2.3 (2.4) | -35.3 (-57.4, -1.8) | .04 |
| Awakening AUC f | 0.6 (5.0) | 0.6 (3.4) | -13.3 (-56.5, 73.0) | .68 |
| Diurnal AUC g | 0.6 (4.7) | 0.6 (3.2) | -6.7 (-52.8, 84.1) | .84 |
| At 22:00 hours | 0.6 (7.6) | 0.5 (3.9) | -1.8 (-55.9, 18.8) | .96 |
| Dexamethasone suppression response h | 0.08 (6.5) | 0.06 (3.9) | -1.1 (-53.5, 103.8) | .97 |
| Ratio of awakening AUC day 2/day 1 i | 0.06 (3.6) | 0.06 (3.2) | -5.6 (-46.7, 67.5) | .85 |
| Ratio of diurnal AUC day 2/Diurnal AUC day 1 j | 0.15 (2.7) | 0.17 (3.1) | -20.4 (-51.4, 30.3) | .36 |
VLBW, very low birth weight (<1500 g)
a Geometric mean, denotes the nth root of the product of n individual values
b Geometric standard deviation, denotes the relative increase in a variable corresponding to one standard deviation unit change in the logarithm of the variable
c Linear regression model 1, adjusted for age and sex
d P for linear regression model 1, adjusted for age and sex
e Peak value after awakening minus value at awakening
f Area under the curve (AUC) ground (above zero), calculated from the first four salivary samples, collected 0, 15, 30 and 60 min after awakening
g AUC ground (above zero), calculated from salivary samples collected 0, 15, 30 and 60 min after awakening and at 12:00, 17:00 and 22:00 hours
h Cortisol upon awakening on day 2 minus day 1, reflects response to the dexamethasone test
i Awakening AUC day 2 minus day 1, back-transformed from log-transformed values, gives the ratio of salivary cortisol after the dexamethasone test
j Diurnal AUC day 2 minus day 1 back-transformed from log-transformed values, gives the ratio of salivary cortisol after the dexamethasone test