Endocrine Abstracts

Introduction: Macroforms of prolactin (PRL), the most often macroprolactin (MaPRL), may be the cause of about 25% cases of laboratory diagnosed hyperprolactinaemia. Macroprolactin is usually quantified by polyethylene glycol precipitation, however, the cut-off value (that means the calculated recovery ratio of monomeric PRL) has not been precisely determined and has rather unsatisfactory diagnostic specificity. Therefore, it is suggested that the evaluation of hyperprolactinaemia should include the assessment of prolactin level after macroforms separation – so called real PRL concentration.

Description of methods: Prolactin concentration was measured with the use of Immulite 1000 analyzer. In 245 sera from patients with hyperprolactinaemia, the separation of macroforms was performed by precipitation method. The cut-off value was assumed 40%, so the hormone recovery ≤40% showed MaPRL dominance in serum and recovery >40% indicated monomeric PRL dominance. Then percentage recoveries of monomeric PRL were compared with real PRL concentrations. Prolactin level after macroforms separation exceeding reference range, showed that monomeric hormone dominate in the sample (true hyperprolactinaemia) and hormone concentration within reference range indicated that macroprolactin was the only cause of hyperprolactinaemia (pseudohyperprolactinaemia).

Results: Hyperprolactinaemia due to the large amounts of MaPRL (recovery ≤40%) were detected in 21 subjects. But in this group, despite the dominance of hormone macroforms, real PRL concentration was elevated above manufacturer’s reference ranges in nine cases (true hyperprolactinaemia). From among 224 subjects with monomeric PRL dominancy in serum (recovery >40%), in 36 persons the real PRL concentration turned out to be within the manufacturer’s reference range (pseudohyperprolactinaemia).

Conclusion: The use of the recovery ratio only to recognize MaPRL dominance as a cause of elevated PRL level, may lead in some subjects to the misclassification of the results and to inappropriate treatment. Therefore, the assessment of real PRL concentration allows to distinguish true and pseudohiperprolactinaemia better.