In the diagnostic approach of hyperprolactinemia three pitfalls or potential confounding problems deserve special attention: pituitary incidentalomas, the hook effect and macroprolactinemia. In as much as 10% of the population aged 20 to 40 years, incidental tumors of the pituitary gland are demonstrated by magnetic resonance imaging. The hook effect is characterized by the finding of falsely low levels of serum prolactin (PRL) when two-site immuno-assays are used in diagnosis in patients with very high prolactin levels. This confusion can be avoided by re-measuring the PRL level in such patients at a 1:100 dilution; PRL levels in samples with the hook effect will then increase dramatically. The hook effect should be excluded in patients with a macroadenoma and PRL levels <200ng/mL. Finally, macroprolactinemia accounts for about 10% of cases of hyperprolactinemia. It results from the predominance of polimeric PRL (also called macroprolactin or big big prolactin) that has decreased bioavailability. Therefore, most patients with macroprolactinemia lack classical symptoms of hyperprolactinemia and usually do not need to be treated.
Hyperprolactinemia; Diagnostic pitfalls; Pituitary incidentalomas; Macroprolactin; Macroprolactinemia; Hook effect
