The role of the procalcitonin test in the diagnosis of infections in immune-mediated inflammatory rheumatic diseases

Objective: to evaluate the role of the procalcitonin (PC) test in the diagnosis of infections in immune-mediated inflammatory rheumatic diseases (IIRDs).

Subjects and methods. The investigation enrolled 325 patients (216 women, 109 men) aged 2 to 82 years with different IIRDs. The serum PC concentration was determined by the quantitative electrochemiluminescence method using a Cobas E 411 analyzer (Roche, Switzerland).

Results and discussion. The infectious process was detected in 145 (44.6%) patients: generalized and local infections in 11 and 134 cases, respectively. Local infections were regarded as severe and mild in 61 and 73 cases, respectively. In patients with generalized infection, the median (Me) PC level was 3.6 [0.88; 11.3] ng/ml. In this group, the PC values exceeded 2 and 10 ng/ml in 73% and 27%, respectively. In severe local infection, the Me PC level was 0.33 [0.23; 0.88] ng/ml, in mild infection — 0.12 [0.05; 0.16] ng/ml. In 180 patients without infection, it was 0.11 [0.05; 0.17] ng/ml, whereas higher PC levels were found in adult onset Still's disease (0.39 [0.14; 0.51] ng/ml), systemic juvenile arthritis (0.17 [0.11; 0.56] ng/ml) and systemic lupus erythematosus (0.11 [0.06; 0.15] ng/ml). The level of PC was significantly higher in the patients with generalized infection than that in those without infection (p<0.0001), as well as in those with mild (p<0.0001) and severe (p<0.0001) local infection. The PC level was higher in patients with severe local infection than in those without infection (p<0.001) and in those with mild local infection (p=0.004). There were no significant differences in PC levels in the patients with mild local infection and in those without infection. The ROC analysis showed that the diagnostic significance of PC determination was excellent in generalized infection, very good in severe local infection, and very good when differentiating generalized from local infection.

Conclusion. Measuring PC is sure to contribute to the diagnosis of generalized and severe local infections in patients with IIRDs. However, when interpreting the PC values, it is necessary to take into account the pooled data: a specific rheumatic nosological entity and clinical, laboratory, and instrumental findings. The multimarker approach can be considered as a promising way to diagnose infections in IIRDs.

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