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

Objective. - 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. Design. - Plasma cortisol and prolactin levels were determined before (T-15) and after a 15-min rest period (TO) 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. Results. - 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 mu g/dl at T-15 vs 16.5 +/- 6.1 mu g/dl at T0, P < 0.0001), in the UK subgroup (18 +/- 6.1 mu g/dl at T-15 vs 16.6 +/- 6.4 mu g/dl at T0, P = 0.0003) but not in men (18 +/- 4.4 mu g/dl at T-15 vs 17.5 +/- 5.8 mu g/dl at T0, P= 0.47) and in the K subgroup (17.8 +/- 4.6 mu g/dl at T-15 vs 17 +/- 5.4 mu g/dl at T0, P= 0.13). At T0, 3.3% and 15% of patients presented values below the cut-off value of 10 mu g/dl (276 nmol/l) and 17 mu g/dl (470 nmol/l), respectively. Conclusion. - These results don't justify intravenous catheterisation with a rest period for plasma prolactin determination in contrast with plasma cortisol determination. (c) 2007 Elsevier Masson SAS. All rights reserved.