Thank you to all who responded to my enquiry about prolactin measurements. “Will you share your approach to the follow-up lab procedures which you use when patients have prolactin results outside the reference range.
We have a two stage protocol. PEG pptation and full gel-filtration. We offer this service to other labs. At what level of prolactin is it worthwhile to perform these additional tests?
Our current SOP states, "ALL samples with Prolactin concentrations above the reference range and with no obvious cause or history, should be referred for macroprolactin screening test eg Males with serum prolactin > 324 mU/L, Non-pregnant females with serum prolactin > 496 mU/L. A recover of >60% is considered negative for macroprolactin. Monomeric Prolactin 41-59% refer sample for further analysis by Gel filtration."
The gel filtration is time consuming and expensive. I feel that it should only be used where there is a substantial increase in total measured prolactin. At what level is it appropriate to employ gel filtration?
We use the Roche cobas Prolactin ll reagent kit, Cat. No. 03203093 190”
I received several useful replies but will quote directly from Paul MacKenzie at Southend. The team there have done much work in this area. Thanks to Paul and Mike Fahie Wilson for responding so comprehensively.
All prolactin requests should be provided with good clinical information about why the test is being done.
Accepting that there are reports that PRL <700 are rarely associated with pituitary tumour but occasionally do occur so recommend PEG ppt if the front line PRL is elevated.
Clinical chemistry reporting and interpretation is based upon reference ranges if results are flagged as abnormal this indicates that action must be taken. If MacroPRL is present then the answer is immediate. There are benefits in immediate further action/follow-up by PEG ppt in reducing the number of consultations and alleviating unnecessary worry for the patient. We adopt a system whereby an elevated frontline PRL reflexes a PEG ppt if the patient has not been screened in the previous 12 months.
There is a positive argument to PEG all high PRL’s if there is a physiological or pharmacological reason for the increased prolactin. MacroPRL may be present in these cases. Frequently, patients present with non-specific symptoms eg infertility ..that could be associated with pituitary tumour which turn out to be MacroPRL cases.
Many laboratories are off the pace expressing results and basing interpretation on recovery. The biggest single action that can be taken to reduce the number of samples referred for GFC is the introduction of Post PEG monomeric PRL reference ranges.
In Serum Total Prolactin and Monomeric Prolactin Reference Intervals Determined by Precipitation with Polyethylene Glycol: Evaluation and Validation on Common ImmunoAssay Platforms Luisa Beltran,1 Michael N. Fahie-Wilson,1 T. Joseph McKenna,2 Lucille Kavanagh,2 and Thomas P. Smith2 Clin Chem 54:10 1673-1681(2008), experimentally derived expected values for Parametric reference intervals for post-PEG prolactin (mIU/L) in male and female sera for each immunoassay platform analyzer are provided. They are;
---------------------Male range.........Female range
----------------------Lower-Upper......Lower-Upper
Centaur-----------61-196 66-278
Elecsys(Cobas)--63-245 75-381
Access-------------70-301 92-469
Architect-----------72-229 79-347
AIA-----------------73-247 83-383
Immulite-----------78-263 85-394
All of the commonly used immunoassays in use are susceptible to macroprolactin interference.
Another helpful reference - a letter Reporting of Post PEG PRL concentrations:Time to change. Clin Chem 56:3 484-485 (2010) authors Thomas Smith and Michael Fahie-Wilson, outlines some of the practical points in the implementation of the Post PEG PRL reference rangesie application, interpretive comments etc.
Using this strategy there are very few GFCs indicated and this procedure can be reserved for concerns around rare cases of IgA MacroPRL where the macromolecule demonstrates incomplete ppt with PEG so appearing as hyperprolactinaemia – A false positive.
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