The use of intravenous catheterisation with a rest period is useful for determination of plasma cortisol levels but not plasma prolactin levels

The use of an intravenous catheter with a rest period has been recommended to avoid false-positive results for hyperprolactinaemia and false-negative results for hypocortisolaemia. We tested the relevance of this recommendation. Plasma cortisol and prolactin levels were determined before (T-15) and after a 15-min rest period (T0) in 119 patients, 38 males (M) and 81 females (F). 52 of the 119 patients were known (K; 30 females and 22 males) and 67 unknown (UK; 49 females and 18 males) to the unit. Prolactin was lower after rest in women (12.3 ± 22.7 ng/l vs 11.7 ± 22.5 ng/ml, P = 0.03), but not in men (6.2 ± 4.5 ng/ml at T-15 vs 5.8 ± 3.2 ng/ml at T0, P = 0.09), in the UK subgroup (10.6 ± 20.7 ng/ml at T-15 vs 10.1 ± 20.9 ng/ml at T0, P = 0.06) and in the K subgroup (10.1 ± 16.7 ng/ml at T-15 vs 9.7 ± 15.8 ng/ml at T0, P = 0.08). None of the patients with prolactin levels higher than 20 ng/ml at T-15 diminished its prolactin value below this cut-off value. Plasma cortisol levels were lower after rest in women (17.9 ± 5.9 μg/dl at T-15 vs 16.5 ± 6.1 μg/dl at T0, P < 0.0001), in the UK subgroup (18 ± 6.1 μg/dl at T-15 vs 16.6 ± 6.4 μg/dl at T0, P = 0.0003) but not in men (18 ± 4.4 μg/dl at T-15 vs 17.5 ± 5.8 μg/dl at T0, P = 0.47) and in the K subgroup (17.8 ± 4.6 μg/dl at T-15 vs 17 ± 5.4 μg/dl at T0, P = 0.13). At T0, 3.3% and 15% of patients presented values below the cut-off value of 10 μg/dl (276 nmol/l) and 17 μg/dl (470 nmol/l), respectively. These results don't justify intravenous catheterisation with a rest period for plasma prolactin determination in contrast with plasma cortisol determination. L'utilisation d'un catheter intraveineux associée à une période de repos est recommandée afin d'éviter les faux positifs de l'hyperprolactinémie et les faux négatifs de l'hypocortisolémie. Nous avons testé la validité de cette recommandation. Le dosage de la prolactine et du cortisol ont été réalisés avant (T-15) et après une période de 15 mn de repos (T0) chez 119 patients, 38 hommes (M) et 81 femmes (F), 52 étaient connus du service (K = known ; 30 femmes et 22 hommes), 67 y venaient pour la première fois (UK = unknown ; 49 femmes et 18 hommes). Les taux de prolactine étaient plus bas à T0 chez les femmes (12,3 ± 22,7 ng/l vs 11,7 ± 22,5 ng/ml, p = 0,03) mais pas chez les hommes (6,2 ± 4,5 ng/ml à T-15 vs 5,8 ± 3,2 ng/ml à T0, p = 0,09), chez les patients venant pour la première fois (10,6 ± 20,7 ng/ml at T-15 vs 10,1 ± 20,9 ng/ml at T0, p = 0,06) et chez