CALCA and idiopathic interstitial pneumonia: Many theories are taken into consideration [2,5], but the exact pathogenesis is unknown; this could be reflected in the pathobiology of LC in patients with IPF and in the PCT levels in patients with LC-IPF. Despite the fact that PCT has been established as a significant biomarker of sepsis and antibiotic stewardship [7], the pathophysiology of PCT production is quite complex [6-9]. Procalcitonin is a prohormone (precursor) of calcitonin (CT).