Background/Purpose: Vitamin D acts as innate and adaptive immune response immunomodulator. 25-hydroxyvitamin D (25OHD) deficiency was reported to be associated with autoimmune diseases flares and also with increased frequency of viral and bacterial infections. Procalcitonin (PCT) is a marker of bacterial and fungal infection and high levels may be related to disease activity in autoimmune diseases. There is no study evaluating simultaneously 25OHD and PCT serum levels in GPA patients and the association with disease activity and infections. The objective of this study is to determine the possible association of 25OHD and PCT serum concentrations with disease activity and respiratory infections in patients with GPA.  

Methods: Thirty-two GPA patients were evaluated in winter/spring (n=32) and summer/autumn (n=27). 25OHD and PCT were measured by electrochemiluminescence. Disease activity was assessed using the Birmingham Vasculitis Activity Score (BVAS≥1) and ANCA. Airways respiratory infection was defined according to the CDC (Centers For Disease Control and Prevention) criteria. T-student, Mann Whitney and Fischer exact tests were performed for statistical analyses, with p <0.05 considered significant.

Results: Fifty three percent (17/32) of patients were women, 65.6% (21/32) were caucasian, with a mean age of 46.2 ± 13yrs, disease duration of 8.9 ± 4.2yrs and 71.8% (23/32) presented generalized form of GPA. Of the 59 samples, 39 (66%) were in vitamin D replacement (800-7,000 U/day). There was no difference between 25OHD concentrations of those with (34.87 ± 12.51 ng/mL) or without (36.31 ± 12.81 ng/mL) vitamin D supplementation. In winter/spring season concentrations of 25OHD were lower compared to summer/autumn (32.31 ± 13.10 vs. 38.98 ± 10.97 ng/mL, p=0.04). Seven patients were diagnosed with airway infections, 5 of them in autumn/winter, with a predominance of tracheobrochitis (71.4%). Patients with airway infection had lower 25OHD concentrations compared with those without infection (24.51 ± 11.81 vs. 36.82 ± 11.98 ng/mL, p=0.01) whereas no difference was observed for PCT serum levels (0.07 ± 0.06 vs. 0.04 ± 0.03 ng/mL, p=0.26). With regard to activity, higher PCT serum levels was observed in patients with concomitant BVAS≥1 and positive ANCA compared with patients BVAS=0 and ANCA negative (0.07 ± 0.06 vs. 0.03 ± 0.01 ng/mL, p=0.02). Further analysis regarding the follow-up of ten patients that presented PCT ≥ 0.05 ng/mL and BVAS ≥ 1, five of them evolved for remission (BVAS = 0) and a decline of PCT was observed; 2 patients remained with active disease and PCT levels remained high (PCT > 0.10). Of note, 25OHD levels were comparable in patients with and without disease activity (BVAS≥1 and positive ANCA), (33.60 ± 11.84 vs. 36.19 ±12.89 ng/mL, p=0.46).

Conclusion: The observed association of low 25OHD levels with airway infection and high PCT levels with activity in patients with GPA suggests that simultaneous measurements of these markers may be helpful to distinguish disease activity from infection in GPA patients.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/simultaneous-measurement-of-25-hydroxyvitamin-d-and-procalcitonin-in-granulomatosis-with-polyangiitis-gpa-differentiation-of-activity-from-infection/