Table 3 shows the results in the 14 patients without acute mast cell mediator release or evidence of mastocytosis from the Sheffield Allergy Clinic. Three of 14 were falsely elevated and had evidence of RF and some HAMA activity. Eleven of 14 samples with undetectable IgM RF levels had tryptase concentrations which were not affected by the action of the HBT tubes. This suggests a lack of heterophile interference and demonstrates the existence

of a cohort of patients in whom unexpectedly raised tryptase levels appear to be real. Care should Palbociclib be exercised in the interpretation of MCT results due to the significant potential for interference by heterophilic antibodies including RF. This study shows that eight

of 56 sera (14%) with MCT > 14 µg/l were confirmed as having falsely elevated MCT. Five of 51 (10%) with MCT > 20 µg/l (WHO minor criteria for SM) were falsely elevated. All false positives had raised levels of IgM RF. Of the cohort with unexplained raised MCT, 20% were false positives due to assay interference but 80% were not, and had truly elevated stable increases of uncertain clinical significance. None of these patients had evidence of mastocytosis on extensive investigation. The persistently raised tryptase in this cohort of patients who do not have any clinical features of mastocytosis is interesting, but any attempts to explain it are speculative. Three of these were false positive elevations due to heterophilic interference from rheumatoid selleck compound factor activity. There do not appear to be any obvious clinical differences that would distinguish these patients from most of our cohort with idiopathic urticaria and angioedema. Longer-term follow-up may be

revealing. MCT is Doxacurium chloride an important marker of acute mast cell mediator release in severe allergic reactions or mastocytosis [9]. It is recognized increasingly that there are some individuals who have persistently elevated tryptase using the current assay but in whom no evidence of either disorder can be found, leading to suspicion of assay interference [1,2,6,10]. However, the manufacturer states that the assay is not affected significantly by heterophile interference. We confirm that the presence of IgM RF correlates with interference in the Phadia tryptase assay and results in overestimation of tryptase or false positivity. This study demonstrates that IgM RF or a HAMA-like activity associated with IgM RF interferes with the assay and leads usually to overestimation of the true MCT value. We confirm that there are patients with persistently raised MCT who appear to be unaffected by HAMA or RF blocking, and these cases are not rare. It is important to note that the values produced following HBT treatment must be interpreted with caution, as this may not remove all the interfering heterophile activity and still give a misleading raised value for the analyte being measured [3].