Identification of IgG-κ type macroprolactin found in the serum of an 8-year-old girl.

We report a case of macroprolactin (macroPRL) in an 8-year-old girl complaining of an enlarged and painful breast who showed elevated PRL levels by enzyme immunoassay.Size-exclusion high-performance liquid chromatography (HPLC) was carried out on a Superose 12 column to estimate the PRL molecular profile. To identify the type of immunoglobulin bound to PRL, immunoprecipitation reactions were performed using three types of anti-heavy chain antibody and two types of anti-light chain.PRL in the patient's serum was eluted at a size slightly larger than the IgG peak by size-exclusion HPLC on a Superose 12 column. In the immunoprecipitation reaction, the PRL concentration of the supernatant mixed with anti-gamma heavy chain and anti-κ light chain was dramatically decreased compared to other types of antiserum. These results indicated that macromolecular PRL was composed of PRL and IgG-κ.A rare case of PRL-IgG-κ-type complex was identified in the serum of the girl and the type of immunoglobulin light chain was determined for the first time. When encountering a child with hyperprolactinemia, pediatricians should take into account the possibility of macroPRL to avoid unnecessary investigation and/or treatment.