Significance of serum procalcitonin for differentiating infections from rheumatic diseases
Differentiation between flare of a rheumatic disease (RD) and the development of infectious process is often extremely difficult due to the similarity of clinical and laboratory manifestations, as well as their lack of specificity.Objective of the study: to assess the significance of procalcitonin (PCT) test as a specific marker of generalized and local infection in patients with RD, and also to determine its role in assessing the inflammatory process activity in various RDs.Material and methods: The case records of 145 patients (101 women, 44 men,  age of 3–79 years), who were undergoing inpatient examination and treatment at Nasonova Research Institute of Reumatology, were examined during the retrospective study. The serum PCT level was determined by the quantitative electrochemiluminescence method using  the Cobas E 411 analyzer (Roshe, Switzerland).Results: The infectious process was diagnosed in 85 patients, the generalized one in 13 and the local one in 72. Local infections were divided into those with the light course – 41 and with the severe course – 31. In patients with generalized infection, the PCT level exceeded 2.0 ng/ml in 77% of cases and  in 10.0 ng/ml in 46.2% of cases.  Median (Me) PCT was 3.6 [2.26; 10.5] in the group with generalized infection. Me PKT exceeded the threshold values   and amounted to 0.49 [0.19; 1.5] ng/ml in the case of a local infection with the severe course,  PCT indices did not significantly differ from those of the group without infection (Me = 0.13 [0.08; 0.25] and 0.09 [0.06; 0.18 ] ng / ml, p> 0.05).with a local infection of the lungs, The maximum values   of PCT in the absence of infection and with a high activity of the rheumatic process were detected in patients with Adult-onset Still’s Disease (AOSD) – Me = 0.26 [0.10; 0.61] ng/ml, moderate increase was detected in patients with systemic-onset juvenile idiopathic arthritis (JIA)– Me = 0.2 [0.14, 0.24] ng/ml, juvenile rheumatoid arthritis (JRA) – Me = 0.2 [0.1; 0.26] ng/ml, systemic lupus erythematosus (SLE) – Me = 0.19 [0.11, 0.39] ng/ml.Conclusions: Determining PCT level undoubtedly contributes to the diagnosis of generalized infections, and differential diagnosis of systemic RD from the infectious process. Further research is required to determine the PCT threshold value for various RDs.