Endocrine Abstracts

Introduction

Current guidelines recommend a single elevated prolactin measurement drawn without excessive venepuncture stress as sufficient for diagnosing hyperprolactinaemia. However, previous studies have demonstrated that the cannulated prolactin test is more reliable at eliminating stress-induced hyperprolactinaemia, thus avoiding unnecessary additional investigations. We routinely perform morning serial prolactin sampling immediately after brachial vein cannulation followed by repeat sampling at 30 and 60 minutes of rest, to rule out stress-induced hyperprolactinaemia.

Objectives

This retrospective study aimed at evaluating the incidence of stress-induced hyperprolactinaemia in females of reproductive age referred to our hospital with isolated mild hyperprolactinaemia on repeat random testing in the community. We investigated any correlation between presenting symptoms and diagnosis of true hyperprolactinaemia and the incidence of pituitary abnormality on MRI.

Methods

All adult female patients, aged between 18–53 years, undergoing cannulated prolactin testing at our Endocrine Unit between 2016 and 2020 were included. Exclusion criteria: presence of macroprolactinaemia, chronic kidney disease, genetic predisposition syndromes, previous diagnosis of pituitary tumours and those with abnormal thyroid biochemistry.

Results

55 patients were eligible, with an average age of 33 years. The mean level of referral prolactin was 979 mIU/l (min: 511, max: 3022, normal range < 496 mIU/l). 40% of patients presented with menstrual disturbances and 32% had galactorrhoea. 58% of patients had a normal prolactin level on cannulated testing, thus confirming stress-induced hyperprolactinaemia. Those with true hyperprolactinaemia were more likely to report galactorrhoea (48% vs. 21%, P < 0.05). 15/32 (47%) patients with stress-induced hyperprolactinaemia were asymptomatic (vs. 26%, P < 0.05). 52% of patients with true hyperprolactinaemia harboured an abnormality on pituitary MRI. Those with a lesion were younger (mean age 30 years vs. 40 years in those with normal MRI, P < 0.05). There was no statistically significant difference in baseline prolactin or symptomatology between the group with normal MRI finding and those with abnormal MRI. Notably 2/5 asymptomatic patients with true hyperprolactinaemia had a microadenoma evident of MRI.

Conclusion

The cannulated prolactin test reliably diagnosed stress-induced hyperprolactinaemia in our select cohort of female patients of reproductive age. Whilst asymptomatic patients are more likely to have stress-induced hyperprolactinaemia, 40% harbour a microprolactinoma if diagnosed with true hyperprolactinaemia on cannulated prolactin testing.