Endocrine Abstracts

Background: Current Endocrine Society guideline recommends a single prolactin level to confirm the diagnosis of hyperprolactinemia. This may lead to over diagnosis and inappropriate imaging. Our institution protocol is to repeat the prolactin and measure macroprolactin. If the second prolactin is elevated, then a cannulated prolactin to role out venipuncture stress effect is undertaken.

Methods: Data were collected for 49 patients between January 2017 to May 2018. After cannula insertion, prolactin is measured at 0, 60 and 120 minutes. Normalization is defined as prolactin drop to normal range.

Results: Mean age was 33.4 years (S.D.±9.9), 44(90%) were female. The presenting symptoms were menstrual irregularities in 28.57% and galactorrhoea in 12.24%, and the rest include fatigue, hirsutism and acne. Overall, mean referral prolactin was 1214.8 milliunit/l (S.D.±677.8) and mean second prolactin was 940 milliunit/l (S.D.±590.3). The cannulated prolactin normalized in 19 (38.8%) patients. Mean second prolactin was 516.4 milliunit/l (S.D.±235.1) in patients who normalized in cannulated prolactin vs 1195 milliunit/l (S.D. ±594.7) in those patients who did not subsequently normalize (P <0.0001). MRI pituitary findings were available for 26/30 patients who did not normalize; 22/26 (84.6%) showed abnormality and four showed normal imaging. Majority of the findings were microadenoma (18/22). Among patients who normalized in cannulated prolactin, four had normal MRI pituitary before referral. In multilogistic regression including age, gender, referral and repeated prolactin, repeated prolactin was the only significant predictor for normalization of cannulated prolactin (P <0.008).

Conclusion: Cannulated prolactin was useful in excluding true hyperprolactinemia in 38.8% of patients with confirmed second elevated prolactin. This confirms that cannulated prolactin results could avoid over diagnosis and unnecessary imaging.