Hemoglobin H disease classification by isoelectric focusing: molecular verification of 110 cases from Thailand.

or other substances in these presumably normal specimens. The Access PRL assay after PEG treatment may be suitable despite the CV of 14% because PEG treatment is frequently used to detect macroprolactin interference (6). It is possible that two samples with low recoveries contained macroprolactin. Our experience with this assay is that samples with PEG recovery values Ͻ60% contain high-molecular-weight prolactin immunoreactiv-ity after gel filtration. The considerable variability seen in the Elecsys PTH and ␤-CTx and the Access GH assays after PEG treatment probably reflects interference by the PEG in the antibody– antigen reactions of these assays. Similarly, although we do not know the mechanism, it appears that HBT treatment can produce a spuriously high recovery of hormone in some assays. The manufacturers state that HBT contains a " unique blocking agent " limited to use for antigen assays to confirm or disqualify an original result in conjunction with other data (such as symptoms and other testing). Our data suggest a further limitation that its use is assay specific, possibly dependent on the assay configuration. We did not observe overrecovery in the three Elecsys assays (all configured with mouse monoclonal antibodies for both capture and detection). It was, however , apparent in the Access assays (LH, FSH, GH, and to a lesser extent, PRL), which contain solid-phase goat–anti-mouse monoclonal antibody complexes for capture and goat antibodies for detection. We believe that these high HBT recovery values are likely to be spurious. The heterophile antibody interference in most immunometric assays is generally positive, leading to lower concentrations after blocking treatments, not increased values as we have mostly observed. Although 30 – 40% of the population may have heterophile antibodies through exposure to animals or monoclonal antibody treatments, the frequency of interference in modern immunoassays is reported to be very low (1, 2). Finally, although we did not investigate all of the specimens with HBT-induced increases in hormone concentrations , we demonstrated that the results were spurious in one case. The specimen outlier detected in the prolactin assay (Fig. 1A) and also showing overrecovery in the Access LH, FSH, and GH assays did not appear as an outlier in any Elecsys assays, or in any assay after PEG treatment. The hormone concentrations of the untreated sample were consistent with those of a " normal " 53-year-old male (7.1 IU/L LH, 12.5 IU/L FSH, 99 mIU/L PRL, and 0.02 mIU/L GH) and were …