PCT levels increase in bacterial infections from an extrathyroidal origin and rise early in course of infection, therefore making it useful biomarker for decision making regarding initiation of antibiotic therapy as results of blood culture are not available immediately.15 One hundred and twenty six blood specimens of critically ill patients admitted with suspicion of sepsis in intensive care unit were analyzed for PCT, CRP, TLC and lactate and compared with blood culture results as gold standard for bacterial infection. This evidence concerns the gene CALCA and bacterial infectious disease.