Interrelationships Between Serum Levels of Procalcitonin and Inflammatory Markers

Abstract Various laboratory markers are utilized in general practice to detect inflammation, and procalcitonin (PCT) has also been routinely measured in many patients as a marker of bacterial infection and sepsis. An increase in PCT starts before an increase in C-reactive protein (CRP), and PCT level is useful not only for the diagnosis of bacterial infection, sepsis, as an indicator of the severity and prognosis of systemic inflammatory diseases, and is also useful for determination of the response to individual treatment. PCT is a precursor of calcitonin and PCT is not produced in a healthy state but is produced by various tissues in septic conditions. Since there are many patients with elevated levels of PCT due to nonbacterial causes, the levels of serum PCT have been apt to be used for a marker for the early detection of not only bacterial infection but also many inflammatory and/or febrile disorders including fever of unknown origin (FUO) in the clinical setting of general medicine. Here we attempted to clarify the differences and similarities of inflammatory markers for a clinical setting. We retrospectively reviewed 359 patients in whom serum PCT had been measured. According to our earlier study, the patients were categorized into 7 groups: bacterial, non-bacterial infection, non-specific inflammation, neoplasm, connective tissue disease (CTD), drug-induced diseases, and unidentified causes. Data for 332 PCT-positive cases including cases of bacterial infection (20.5%), non-specific inflammation (20.8%), neoplasm (9.9%), CTD (8.4%), and non-bacterial infection (7.2%) were used for analysis. Serum PCT level was highest in the bacterial infection group (1.94 ng/ml) followed by the non-specific inflammatory group (0.58 ng/ml) and neoplastic diseases group (0.34 ng/ml). Of note, serum PCT level was positively correlated with serum levels of C-reactive protein (R2=0.39), soluble interleukin-2 receptor (sIL-2R; R2=0.48), and ferritin, plasma level of D-dimer level and white blood cell count, whereas it was negatively correlated with serum albumin level (R2=0.27), hemoglobin concentration and platelet count. The result of the strongly positive correlation with serum level of sIL-2R suggested that an increased serum PCT level may indicate not only an inflammatory state but also a neoplastic state such as malignant lymphomas in the diagnostic process of various inflammatory disorders in a clinical setting of general practice for diagnosing febrile conditions.