Changes to Prolactin Assay

For the prolactin (plasma) assay [Epic: LAB531] run in the Clinical Chemistry core laboratory, there has been a policy for years to test all samples above the upper limit of the gender-specific prolactin reference range for the presence of interference by macroprolactin (prolactin bound to IgG). This is done by running a separate polyethylene glycol (PEG) precipitation on the sample, which eliminates interference caused by macroprolactin. If the PEG-treated sample gives a result less than 50% of the original value, then the discrepancy is appended to the result. The main drawback to this process is that the PEG precipitation is labor-intensive and delays results.

We have done an analysis of 2,350 prolactin values outside the reference range for the past several years and have not found any instance where the PEG treatment led to a greater than 50% change in value (thus no comment appended to results). This likely relates to the improvements in assay antibodies relative to years ago when macroprolactin interference was more common. Some clinical services have expressed concerns about the delay in prolactin results, which can especially problematic if imaging or surgical procedures are influenced by the results.

Effective Tuesday, September 14, 2010, we will eliminate the routine practice of testing samples with elevated prolactin for the presence of macroprolactin. Instead, there will be a new orderable in Epic called "Macroprolactin Check" (LAB7438). This order will determine and report the total prolactin plasma concentration and, if elevated above the gender-specific reference range, will do the PEG precipitation process to check for macroprolactin. A drop in prolactin concentration of greater than 50% following PEG treatment indicates the presence of significant amounts of macroprolactin and will be reported as "POSITIVE". The PEG precipitation will NOT be performed if the total prolactin concentration is within the gender-specific reference range.

The Macroprolactin Check can also be ordered as an add-on to a sample that has a previous (total) prolactin result greater than the upper limit of the appropriate reference range. The add-on order may be clinically appropriate if the plasma prolactin concentration is elevated to a degree that seems discordant with clinical findings.

Questions should be directed to Matthew Krasowski, MD, PhD, medical director of the Clinical Chemistry