Hook-effect in the endocrinology practice: case-report

Abstract

In this study, we described a case that illustrates the clinical significance of the hook-effect, a laboratory phenomenon when the measured hormone level is falsely lowered due to the binding of signaling antibodies with high analyte concentration. In a patient with a newly diagnosed 2.7 x 1.7 x 2.1 cm pituitary macroadenoma, laboratory testing revealed an increase in prolactin level to 878.6 mMU/ml (105.0–540.0 mMU/ ml). The abnormality was interpreted as a secondary increase hyperprolactinemia due to pituitary stalk compression, and the patient was referred for surgery. Upon admission to the hospital, the prolactin level was measured repeatedly using a more modern test system and the level was 2 296.0 ng/ml (4.0–15.2) without detecting a significant amount of macroprolactin. The degree of hyperprolactinemia indicated the presence of macroprolactinoma. The patient was discharged from the neurosurgical department with a recommendation to start dopamine agonists treatment, which showed an excellent biochemical response. A personalized approach to the differential diagnosis of hyperprolactinemia, which takes into account not only a wide range of pathological conditions, but also a number of laboratory phenomena, reduces the risks of unjustified surgical interventions in patients with prolactinomas.