Biochemical diagnosis of monomeric hyperprolactinemia

Prolactin can take several molecular forms of which the most biologically active is the monomeric form (PRLm). The presence of macroprolactin (MPRL) can give rise to a false diagnosis of hyperprolactinemia due to interference in the measuring procedure. The aim was to develop a protocol that enables diagnosis of monomeric hyperprolactinemia, which should also be complementary to the procedure for detecting MPRL. The reference population for PRLm was made up of 122 healthy women and 140 healthy men, from whom blood was extracted for PRL quantification. Additionally, 49 hyperprolactinemic serums (33 women and 16 men) were collected. PRL was quantified in all the samples in an Immulite 2000. The detection of MPRL and PRLm was carried out following precipitation with polyetylenglicol (PEG). The result was confirmed by gelatin filtration chromatography. The reference values were obtained following the indications of the Expert Panel of the IFCC. The PRLm reference values were 3,4 - 26,6 µg/L and 4,6 - 16,4 µg/L in women and men, respectively. In 57% of the 49 hyperprolactinemic patients the concentration of PRLm following PEG fell outside the previously obtained reference interval, confirming the presence of monomeric hyperprolactinemia. A protocol for quantifying PRLm has been developed and implemented. Obtaining PRLm reference values makes it possible to diagnose monomeric or active hyperprolactinemia in a complementary form to the identification of MPRL.