Detection and Evaluation of Procalcitonin Variants As Diagnostic Tools in Systemic Inflammation

BACKGROUND: Procalcitonin is an indicator of systemic inflammation associated with major surgery or sepsis. Procalcitonin exists in a full-length and truncated variant as a result of dipeptidylpeptidase-4 (DPP4)-cleavage. We recently identified differential biological activity of both variants. Here, we present an immunoassay-based method for the separate detection of procalcitonin variants and correlation to clinical data in patients with severe systemic inflammation. METHODS: Rabbits were immunized with peptides of N-terminal sequences of both human procalcitonin variants and polyclonal antibodies purified from rabbit plasma. Antibodies were used for the detection of procalcitonin variants in an indirect sandwich enzyme-linked immunosorbent assay (ELISA) using a commercially available monoclonal anti-procalcitonin antibody as capture. Serum was collected from 19 septic patients exhibiting hyperprocalcitonemia as part of a cross-sectional study; clinical data were analyzed and correlated with procalcitonin variant measurements. DPP4 activity was determined by a DPP4 activity assay. RESULTS: Purified antibodies allowed for the separate detection of both procalcitonin variants in all patients. Levels of truncated procalcitonin (truncPCT) correlated with DPP4-activity (Pearson’s R = 0.85, P < .001) and negatively correlated with patients’ Sequential Organ Failure Score (SOFA) scores (Pearson’s R = –0.56, P = .013). In contrast, the correlation between full-length procalcitonin (fullPCT) and SOFA scores was positive (Pearson’s R = 0.56, P = .013). Separation of the patient collective into groups with higher amounts of fullPCT versus truncPCT revealed higher SOFA scores in patients with fullPCT > truncPCT (mean ± standard error of the mean; 11. 3 ± 0.8 vs 6. 1 ± 1.5, P = .003). Patients with fullPCT > truncPCT showed a tendency towards higher doses of vasopressor (0. 2 ± 0.1 vs 0. 1 ± 0.03 µg/kg/min norepinephrine within the first 24 hours after sepsis diagnosis, P = .062) and exhibited higher creatinine (2. 0 ± 0.2 vs 1. 4 ± 0.3mg/dL, P = .019) and leukocyte levels (31. 0 ± 5.4 vs 12. 8 ± 1.9cells/µL, P = .012). In addition, patients with fullPCT > truncPCT were more often subjected to treatment with hydrocortisone (49.0 vs 0%, P = .018). CONCLUSIONS: Polyclonal antibodies generated using procalcitonin N-terminal variant peptides as immunogens are suitable for procalcitonin variant assessment. The separate detection of procalcitonin variants may offer additional diagnostic value and can be correlated with organ dysfunction and clinical outcomes in patients with systemic inflammation.