[OA-13] Inappropriate use of dilute prolactin testing

Krit Achaloetvaranon¹, Paweena Chunharojrith² and Busadee Pratumvinit¹

1. Department of Clinical Pathology, Facolty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
2. Division of Endocrinology and Metabolism, Department of Medicine, Facolty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand

Prolactinoma is the most common cause of pathologic hyperprolactinaemia. The tumour size usually correlates with the prolactin level. Extremely high prolactin levels might cause the hook effect, resolting in erroneously low readings. In patients with pituitary adenomas (≥ 3 cm) and normal to modestly elevated prolactin levels, a 100-fold sample dilution is required to eliminate the hook effect. The aim of this study was to evaluate inappropriate requests of dilution prolactin test (dPRL) at Siriraj hospital, to compare the rate before and after dPRL ordering was formally separated, and to estimate the prevalence of the hook effect. We defined the appropriate ordering criteria for dPRL. We conducted a retrospective review of dPRL ordering between May 2010 and April 2020. Of 440 patients, 20.2% had prolactinoma. From 864 specimens, the inappropriate requests were 81.1% (95% CI: 78.3 – 83.7). After separating dPRL ordering, the number of dilute prolactin requests increased from 1.8 to 5.7% and the rate of appropriateness declined dramatically from 20.5 to 14.0%. Throughout the 10-year study period, no evidence of the hook effect was observed. In conclusion, the inappropriate rate of dPRL test ordering is substantial. Communication between laboratory staff and physicians is critical to the appropriate laboratory use.

Keywords: appropriate use; dilute prolactin; hook effect; hyperprolactinaemia; prolactinoma