Background/Purpose:   The prognosis of the ANCA associated vasculitis (AAV) has improved with the new immunosuppressive treatments but infectious complications remain frequent. Procalcitonin (PCT) is used for a quick diagnosis of bacterial infection. The aim of this study was to assess the diagnostic accuracy of PCT for the differential diagnoses of a bacterial infection from a vasculitis flare.

Methods:  All patients with a granulomatosis with polyangiitis (GPA), a eosinophilic granulomatosis with polyangiitis (EGPA) or a microscopic polyangiitis (MPA) followed in our internal medicine department were included. PCT was determined by KRYPTOR assay (Thermo Fisher BRAHMS). All bacterial infections or flares up of the vasculitis were recorded. The diagnosis of flare up was based on increase of the BVAS or the BVAS WEG. Infections were confirmed by a positive microbial test or an evidence of infection on imaging. For the cases without evidence of positive microbial test, the diagnosis was established when two out of three practitioners of the unit gave the same opinion.

Results:  The cohort consisted of 99 AAV (GPA = 73; EGPA = 21; MPA = 5). The follow up was of 5 years [1,8 ; 9,2]. 53 patients experienced 96 flare ups. Those were GPA in 70% of cases. 57 patients developed 74 bacterial infections. 11 were excluded because of a lack of proof. 27 had a positive microbial test. The value of PCT was found for 55,4% of the registered events. PCT was higher in cases of bacterial infection than flare up (0,3 µg/l [0,11 ; 1,9] vs 0,08 µg/l [0,05 ; 0,13], p<0,0001). The same results were found for the bacterial infection with a proof by positive microbial test (0,55 µg/l [0,13 ; 3] vs 0,08 [0,05 ; 0,13], p=0,0021). For a threshold in 0,11µg/l, the sensibility and the specificity of the PCT were of 75% and 73,5% respectively. For a threshold of 48mg/l, the sensibility of the CRP was 71,4% and the specificity was 62,8%.

Conclusion:  Five retrospective studies were carried on this subject. For two studies, the result seems to show an increase of procalcitonin during active vasculitis. But this result is inconstant and uncertain. Three studies found results similar to ours; during bacterial infections, the PCT increase more than during flares. Therefore, a modification of the discriminant threshold could allow the using of this marker to distinguish a flare up of infection. One study that used the same assay to determine the PCT, showed that a threshold of 0,1 µg/l was effective. The accuracy of PCT for the diagnosis of bacterial infection in patients with AAV is better than CRP. PCT seems to be useful to distinguish a flare up from a bacterial infection although PCT rises too in flare up.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/interest-of-procalcitonin-for-the-follow-up-of-anca-associated-vasculitis-data-from-a-cohort-of-99-patients/