BIOCHEMISTRY
Verifying a legacy macroprolactin assay in an NHS biochemistry laboratory
Elena Cohen recounts the process of optimising and incorporating a challenging legacy macroprolactin assay, internal quality control and its subsequent verification ahead of implementation.
I suspect we’ve all had one of those uncomfortable moments in our careers. The kind where a small but irritating problem quietly lands on your desk. Nobody really understands it, nobody particularly wants to deal with it, but somehow it has become your problem. It’s your section, your responsibility, and saying “no” isn’t really an option. For many NHS biochemistry
laboratories, macroprolactin testing falls squarely into that category. It is rarely anyone’s favourite assay. The method has often been in use for years – sometimes decades. Staff perform it because that’s how it has always been done, the rationale
has faded into folklore, and nobody quite remembers from where the protocol came. Biomedical scientists, accustomed to highly automated analysers processing hundreds of samples an hour, tend to view a manual polyethylene glycol (PEG) precipitation with all the enthusiasm usually reserved for performing monthly analyser maintenance. Support workers quite rightly point out that the dilutions and interpretation often fall outside their scope of practice. The task frequently finds its way to assistant practitioners, who perform it diligently but are unlikely to nominate it as the highlight of their working day.
3d structure of prolactin (PRL) from PDB 1N9D from two orthogonal viewpoints.
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WWW.PATHOLOGYINPRACTICE.COM September 2026
In many laboratories, macroprolactin has quietly become the assay that everyone hopes someone else will do. Then three months ahead of your next UKAS visit, the clinical scientist gives you one deceptively simple instruction: “Please verify the method.” And that’s the moment you feel that stomach sinking sensation.
Background Prolactin is a polypeptide hormone synthesised and secreted primarily by lactotroph cells of the anterior pituitary gland. As a member of the growth hormone/prolactin family, it plays a vital role in reproduction function, lactation, metabolism and immune regulation. The most common hormonal
disorder of the pituitary gland is hyperprolactinaemia, and it is defined as persistently elevated circulating prolactin levels. Its clinical significance is largely atributable to its effects on gonadal and mammary function, resulting in anovulatory infertility, menstrual disturbances, sexual dysfunction, and galactorrhoea. The measurement of serum
prolactin concentration is fundamental to the diagnosis and management of hyperprolactinaemia and most clinical laboratories measure serum prolactin concentrations using two- site sandwich immunoassays based on chemiluminescent technology. These
C.Keeler et al. (2003). doi:10.1016/S0022-2836(03)00367-X. Public domain
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