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Letters |
Department of Clinical Chemistry Southend Hospital Prittlewell Chase Westcliff-on-Sea Essex SS0 0RY United Kingdom Fax 44-1702-221059
To the Editor:
John et al. (1) presented two clinical cases
demonstrating the diagnostic confusion created by cases of
hyperprolactinemia that are attributable to the presence of
macroprolactin. The authors urged manufacturers of prolactin (PRL)
reagents to (a) indicate in their product literature the
extent to which macroprolactin interferes in their assays, and
(b) have available a validated method to confirm the
presence of macroprolactin. Considerable progress has been made in both
of these issues since the distribution of serum from one of the
cases presented by John et al. (1) by the United
Kingdom National External Quality Assessment Scheme (UKNEQAS)
(2); however, most of the data have been presented only in
preliminary form. A more recent UKNEQAS distribution of a serum
containing macroprolactin (2) provided data on more recently
introduced assays, as well as on a wider range of assays (Table 1
), and showed a pattern of reactivity in PRL assays similar to
that presented by John et al. (1). The Roche Elecsys PRL
assay (2) reacted strongly with macroprolactin in this
sample, as indicated by product literature.
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Polyethylene glycol (PEG) precipitation has been validated as a technique for detection of macroprolactin with the Elecsys PRL assay (3). PEG precipitation has also been validated for use with the Bayer Immuno-1 PRL assay (4). These data have been presented at user group meetings, and guidance has been issued to users in the United Kingdom. The recently introduced Abbott Architect PRL assay reacts strongly with macroprolactin, and PEG precipitation has also been validated with this assay (5).
PEG interferes in the Abbott AxSYM PRL assay, but preliminary
communications (6)(7) have described detection
of macroprolactin by centrifugal ultrafiltration with this assay, and a
full publication is in preparation. In the Wallac Delfia assay,
macroprolactin has been identified as the cause of hyperprolactinemia
in 15–17% of patient samples with increased serum PRL
(8). In the Elecsys and Architect assays, macroprolactin has
been identified as the cause of hyperprolactinemia in 16–17% of
patient samples with increased serum PRL (3)(5).
Preliminary results indicate a similar prevalence with the Immuno-1
(4), and it seems probable that this can be expected with
all of the relatively strongly reacting assays in Table 1
.
The Bayer/Chiron PRL assays on the ACS:180 and Centaur analyzers have been considered low-reacting assays with regard to the presence of macroprolactin, as illustrated by the serums distributed through UKNEQAS (1)(2). The differences between the results of relatively high- and low-reacting assays have been taken as an indication of the presence of macroprolactin in samples. Inspection of estimates of monomeric PRL by gel-filtration chromatography in these samples suggests that although the Bayer/Chiron PRL assays react with the macroprolactin present, these assays generally react to a lesser extent than others. The structure of macroprolactin is variable (9), and the reaction of PRL assays with macroprolactin is also variable (4)(10). The Bayer/Chiron PRL assays may react strongly with the macroprolactin in some patient samples, and concordance of results with other assays does not exclude macroprolactin as a cause of hyperprolactinemia. PEG interferes in the Bayer/Chiron PRL assays, and further work is needed to (a) establish the prevalence of macroprolactin as a cause of hyperprolactinemia with these assays, and (b) develop a method for detecting macroprolactin in these assays.
The distribution of specimens containing macroprolactin through UKNEQAS has provided valuable information on the response of PRL assays to macroprolactin. This distribution has also heightened awareness of macroprolactin and encouraged laboratories to consider and investigate macroprolactin as a possible cause of hyperprolactinemia. In the most recent distribution, 49% of respondents considered macroprolactin as a potential cause of hyperprolactinemia, and 5% of respondents who used assays that reacted strongly with the macroprolactin investigated and detected the presence of macroprolactin. Greater awareness of the problem is still required, but considerable progress has been made.
References
Department of Medical Biochemistry, University Hospital of Wales, Heath Park, Cardiff CF14 4XW, United Kingdom, Fax 44-29-20748383, E-mail rhys.john{at}cardiffandvale.wales.nhs.uk
To the Editor:
Fahie-Wilson and major equipment manufacturers have done valuable work, but more than one-half of all participants failed to recognize that macroprolactin could be a cause of hyperprolactinemia. New assays are needed that react only with monomeric prolactin. Some prolactin assays are already minimally affected by the presence of macroprolactin (1). Interferences in immunoassays remain important and put patients at risk of unnecessary surgical intervention (2). Continued refinement of prolactin immunoassays is needed.
References
The following articles in journals at HighWire Press have cited this article:
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  L. Beltran, M. N. Fahie-Wilson, T. J. McKenna, L. Kavanagh, and T. P. Smith Serum Total Prolactin and Monomeric Prolactin Reference Intervals Determined by Precipitation with Polyethylene Glycol: Evaluation and Validation on Common ImmunoAssay Platforms Clin. Chem., October 1, 2008; 54(10): 1673 - 1681. [Abstract] [Full Text] [PDF]
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L. Kavanagh, T. J. McKenna, M. N. Fahie-Wilson, J. Gibney, and T. P. Smith Specificity and Clinical Utility of Methods for the Detection of Macroprolactin Clin. Chem., July 1, 2006; 52(7): 1366 - 1372. [Abstract] [Full Text] [PDF]
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J. Schiettecatte, A. Van Opdenbosch, E. Anckaert, J. De Schepper, K. Poppe, B. Velkeniers, and J. Smitz Immunoprecipitation for Rapid Detection of Macroprolactin in the Form of Prolactin-Immunoglobulin Complexes Clin. Chem., September 1, 2005; 51(9): 1746 - 1748. [Full Text] [PDF]
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R. Sapin and G. Kertesz Macroprolactin Detection by Precipitation with Protein A-Sepharose: A Rapid Screening Method Compared with Polyethylene Glycol Precipitation Clin. Chem., March 1, 2003; 49(3): 502 - 505. [Full Text] [PDF]
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