Serial prolactin sampling as a confirmatory test for true hyperprolactinemia

Hyperprolactinemia may be due to physiological or pathological causes, and may be asymptomatic or induce hypogonadism, infertility, and/or galactorrhea. It is important to take prolactin samples while avoiding stress, as this may increase prolactin levels. Therefore, our aim was to assess the value of prolactin serial sampling after brachial vein cannulation.

Sixty-six patients (34.9±11.8 years of age, 92.4% female) with an initial elevated random prolactin level were included. A prolactin sample was drawn at baseline and after a 30min rest.

The median referral prolactin level was 37.4ng/ml (interquartile range [IQR* 23.3), the baseline prolactin level at serial sampling was 19.5ng/ml (IQR 8), and the value after a 30min rest was 17.1ng/ml (IQR 7.9). Hyperprolactinemia was not confirmed by serial sampling in 45 patients (68.2%). There were no statistically significant differences in referral prolactin levels between patients with and without confirmed hyperprolactinemia (41.2ng/ml and 36.7ng/ml respectively, p=0.3). Galactorrhea was found in 13.6% of patients, amenorrhea or oligomenorrhea in 28.8%, infertility in 7.6%, erectile dysfunction in 4.6%, and gynecomastia in 3%, while 45.5% were asymptomatic. There were no statistical differences regarding the presence or absence of any of these symptoms and subsequent confirmed hyperprolactinemia. Fifty-seven patients (86.4%) were discharged after the results of the prolactin serial sampling were obtained.

Prolactin serial sampling may be a useful test to detect artefactual hyperprolactinemias, thus avoiding unnecessary additional tests and treatments.