Objective: Hyperprolactinaemia is one of the most common disorders of the hypothalamic-pituitary axis. Endocrine Society guidelines state that a single prolactin measurement in a blood sample obtained at any time of day is adequate to confirm hyperprolactinaemia. However, prolactin levels can be confounded by physiological stimuli, e.g sleep, stress or exercise. Our objective was to assess the clinical significance of prolactin level obtained via cannulated prolactin test compared to a single non-rested prolactin sample obtained by venepuncture.
Methodology: A retrospective analysis was carried out for all patients referred to the Endocrine Department for hyperprolactinaemia and underwent cannulated prolactin test between June 20162017. A cannula was inserted and a cannulated prolactin sample was withdrawn 60 minutes after bed-rest through the cannula. The prolactin on referral was used as the non-rested sample for comparison. Normal range prolactin <496 mIU/L.
Results: Thirty patients (23 female, 7 male) with a mean age (+/−SD) of 34.4 years (+/− 7.3 years) were included. 13 out of 30 had no associated symptoms. Mean referral prolactin was 796 mU/L (+/−280 mU/L) compared to mean cannulated prolactin 400 mU/L (+/−178 mU/L). Only 8 out of 30 patients had true hyperprolactinaemia with elevated cannulated prolactin levels. Meanwhile, 22 out of 30 (73%) patients had normal cannulated prolactin measurements. Among the 22 patients with normal cannulated prolactin, 5 of them had MRI pituitary performed prior to referral and cannulated prolactin level taken and were reported normal.
Conclusion: Cannulated prolactin measurement is useful in excluding true hyperprolactinaemia in 73% of patients with high referral prolactin measurements. Furthermore our study suggests samples taken at 60 mins are sufficient for a resting cannulated sample to be taken. Undertaking a cannulated prolactin in such patients may considerably reduce the number of MRI scans performed.