Poster Presentation ESA-SRB-APEG-NZSE 2022

The utility of rested prolactin sampling in the evaluation of hyperprolactinaemia (#311)

Tom Wilkinson 1 , Bobby Li 1 , Steven Soule 1 , Penny Hunt 1
  1. Canterbury District Health Board, Christchurch, NZ, New Zealand

Introduction

Serum prolactin may be elevated by venepuncture stress(1).  We investigated the utility of a rested prolactin sample, obtained through an indwelling venous cannula, in preventing overdiagnosis of hyperprolactinaemia.

Methods

Patients at our institution undergo serial prolactin sampling through an indwelling venous cannula, usually over 40 minutes, when investigating hyperprolactinaemia.  We retrospectively reviewed all serial prolactin sampling performed during a three-year period.  Patients taking interfering medications were excluded.  Macroprolactin interference was excluded.  The main outcome was normalisation of serum prolactin during serial sampling.

Results

103 patients with documented hyperprolactinaemia (range 360-1690mU/L) were included in the analysis.  50 had a normal prolactin at the start of serial sampling, 10 had an initially elevated prolactin that normalised during serial sampling, and 43 had sustained hyperprolactinaemia.  The final prolactin was lower than the initial prolactin in 82 patients (80%, p<0.001), suggesting a prevalent effect of venepuncture stress.  49 patients (98%) with a normal prolactin at the start of serial sampling also had a normal prolactin at the end of serial sampling, suggesting the initial prolactin did not provide information additional to that provided by the final (rested) prolactin.  Referral prolactin level was only modestly predictive of the likelihood of normalisation on serial sampling (AUC 0.65 females, 0.88 males, p<0.05 for both).

Conclusion

Serum prolactin is frequently elevated by the stress of venepuncture.  Confirmation of hyperprolactinaemia in a rested sample, obtained from an indwelling venous cannula, prevents inappropriate investigation with significant associated costs and potential for unnecessary treatment.

We have changed our testing protocol for hyperprolactinaemia on the basis of these results, obtaining a single (rested) sample after 40 minutes rather than multiple (serial) samples, which we believe to be a novel approach.  This reduces cost, simplifies interpretation of results, and mirrors the practice of obtaining a single rested sample for plasma metanephrines(2).

  1. Melmed S, Casanueva FF, Hoffman AR, Kleinberg DL, Montori VM, Schlechte JA, Wass JA. Diagnosis and treatment of hyperprolactinemia: An Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2005;96:273-288.
  2. Kline GA, Boyd J, Polzin B, Harvey A, Pasieka JL, Sadrzadeh HSM, Leung AA. Properly collected plasma metanephrines excludes PPGL after false-positive screening tests. J Clin Endocrinol Metab. 2021;106(8):e2900-2906.