Prolactin Immunoreactivity in Rheumatoid Factor-Containing Specimens: Is it Prolactin, Macroprolactin or Assay Interference?

Specimens containing Rheumatoid factor (RF) were examined for possible interference in Prolactin (PRL) measurement. PRL levels following polyethylene glycol (PEG) treatment were significantly lower than in untreated RFpositive samples (p<0.001; n=43) and spurious hyperprolactinemia was indicated in 7 percent. Gel filtration chromatography suggested that the PRL-like immunoreactivity was from assay interference rather than a macroPRL complex and that PEG treatment successfully removed the interference. It is important that laboratories consider explanations other than macroPRL when interpreting PRL results following PEG treatment.