Importance of cannulated prolactin test in the definition of hyperprolactinaemia

Purpose Recent guidelines suggest that a single prolactin measurement is adequate to confirm hyperprolactinaemia. This may lead to unnecessary investigation of artefactual hyperprolactinaemia. Prolactin measurement drawn from an indwelling cannula after rest removes stress as a con-founding variable. The objective was to determine the frequency of true hyperprolactinaemia amongst patients referred following a single prolactin measurement. Methods A cannulated study was considered if prolactin on referral(‘ReferralProlactin’)was\5,500 mU/L(260 ng/mL) but [410 mU/L (19 ng/mL) in males or [510 mU/L (24 ng/mL) in females, irrespective of clinical context. Case-notes of 267 patients undergoing cannulated prolactin measurement over a 10-year period (2000–2010) were reviewed. Pre-existing pituitary disease, dopamine antago-nist use, and macroprolactinaemia were excluded. Morning ante-cubital vein cannulation was followed immediately by withdrawal of ‘Repeat Prolactin’ sample. After 120-min bed-rest, ‘Resting Prolactin’ was withdrawn through the cannula. Results 235 patients were included for analysis. 64 (27 %) were within normal range; following Repeat Prolactin in 41 (17 %) and Resting Prolactin in 23 (9 %) cases. Referral Prolactin was higher in patients with true hyperprolactina-emia, 1,637 ± 100 mU/L (77.2 ± 4.7 ng/mL) than with artefactualhyperprolactinaemia,1,122 ± 68 mU/L(52.9 ± 3.2 ng/mL; P\0.001) but there was substantial overlap. 21 out of 171 cases (12 %) with true hyperprolactinaemia had a macroadenoma. Presenting symptoms did not pre-dict true hyperprolactinaemia. Referral Prolactin of 2,000 mU/L (94 ng/mL) had 97 % specificity to identify true hyperprolactinaemia. Conclusions Reliance on a single, non-rested prolactin value may lead to over-diagnosis of hyperprolactinaemia. A resting sample should be considered with random values \2,000 mU/L (94 ng/mL)

Importance of cannulated prolactin test in the definition of hyperprolactinaemia

Purpose Recent guidelines suggest that a single prolactin measurement is adequate to confirm hyperprolactinaemia. This may lead to unnecessary investigation of artefactual hyperprolactinaemia. Prolactin measurement drawn from an indwelling cannula after rest removes stress as a con-founding variable. The objective was to determine the frequency of true hyperprolactinaemia amongst patients referred following a single prolactin measurement. Methods A cannulated study was considered if prolactin on referral(‘ReferralProlactin’)was____5,500 mU/L(260 ng/mL) but [410 mU/L (19 ng/mL) in males or [510 mU/L (24 ng/mL) in females, irrespective of clinical context. Case-notes of 267 patients undergoing cannulated prolactin measurement over a 10-year period (2000–2010) were reviewed. Pre-existing pituitary disease, dopamine antago-nist use, and macroprolactinaemia were excluded. Morning ante-cubital vein cannulation was followed immediately by withdrawal of ‘Repeat Prolactin’ sample. After 120-min bed-rest, ‘Resting Prolactin’ was withdrawn through the cannula. Results 235 patients were included for analysis. 64 (27 %) were within normal range; following Repeat Prolactin in 41 (17 %) and Resting Prolactin in 23 (9 %) cases. Referral Prolactin was higher in patients with true hyperprolactina-emia, 1,637 ± 100 mU/L (77.2 ± 4.7 ng/mL) than with artefactualhyperprolactinaemia,1,122 ± 68 mU/L(52.9 ± 3.2 ng/mL; P____0.001) but there was substantial overlap. 21 out of 171 cases (12 %) with true hyperprolactinaemia had a macroadenoma. Presenting symptoms did not pre-dict true hyperprolactinaemia. Referral Prolactin of 2,000 mU/L (94 ng/mL) had 97 % specificity to identify true hyperprolactinaemia. Conclusions Reliance on a single, non-rested prolactin value may lead to over-diagnosis of hyperprolactinaemia. A resting sample should be considered with random values ____2,000 mU/L (94 ng/mL)