title: Circulating myeloperoxidase may cause false negative findings in the analysis of myeloperoxidase antibodies in systemic vasculitis.
abstract: In systemic vasculitis reliable detection of myeloperoxidase antibodies (MPO-Abs) is of great clinical importance in the diagnosis and follow-up of patients. We have studied whether circulating myeloperoxidase (MPO) could have an effect on MPO-Ab findings. Serum MPO and MPO-Abs were measured in 50 healthy individuals, 35 patients and in the follow-up samples from two patients with Wegener's granulomatosis. Heating the sera at 56 degrees C for 30 min reduced the concentration of immunoreactive MPO both in control and patient sera. In 71% of the patient sera heating made initially negative MPO-Abs detectable. In a few cases with severe vasculitis the antibody findings remained totally negative. These results, together with the data from the follow-up samples from two patients with Wegener's granulomatosis, revealed that the serological diagnosis of vasculitis may be considerably delayed if only native samples are analysed for MPO-Abs. These findings are of considerable clinical significance for the interpretation of MPO-Ab results. Circulating myeloperoxidase affects MPO-Ab measurements, causing false negative findings in MPO-Ab assays. Therefore, it is recommended to denaturate circulating MPO by heating the sera before the analysis of MPO-Abs and to re-evaluate the cut off-values.
authors.affiliation: Department of Clinical Microbiology, University Hospital of Tampere, Finland.
authors.forename: A M
authors.initials: AM
authors.lastname: Haapala
authors.forename: E
authors.initials: E
authors.lastname: Soppi
authors.forename: H
authors.initials: H
authors.lastname: Hyöty
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001323:Autoantibodies / Q000097:blood*; D005188:False Negative Reactions; D005260:Female; D005500:Follow-Up Studies; D014890:Granulomatosis with Polyangiitis / Q000097:blood / Q000201:enzymology / Q000276:immunology; D006358:Hot Temperature; D006801:Humans; D008297:Male; D008875:Middle Aged; D009195:Peroxidase / Q000097:blood* / Q000276:immunology / Q000494:pharmacology; D014657:Vasculitis / Q000175:diagnosis* / Q000201:enzymology / Q000276:immunology
chemical_list: D001323:Autoantibodies; D009195:Peroxidase