K. R. has been reimbursed by B. R.A. H.M. S. Diagnostica GmbH, the manufacturer of procalcitonin, for organizing educational symposia, research projects, speaking, and consulting. M. M. has received funds for research and fees for speaking from B. R
IntroductionSevere infections and sepsis are common causes of morbidity and mortality in intensive care units. Such conditions are accompanied by clinical and laboratory signs including changes in body temperature, leukocytosis, and tachycardia. However, these manifestations of systemic inflammation may be noninfectious in origin and are neither specific nor sensitive for sepsis. A similar inflammatory response occurs in patients suffering from pancreatitis [1], major trauma [2], and burns [3] without infectious complications. It is therefore frequently difficult to distinguish between patients in organ dysfunction or shock who have systemic infection and those who do not [4]. Bacteriological evidence of infection may not develop concurrently with clinical signs of sepsis. Positive bacteriological results may be due to contamination, and negative results do not exclude the presence of infection or sepsis. Since these standard clinical and laboratory parameters lack sensitivity and specificity, other markers are needed to provide an early indication of an infectious cause of a generalized inflammatory response, and thus allow early diagnosis and more specific therapeutic interventions. One such parameter, procalcitonin, has recently gained interest as a possible marker of the systemic inflammatory response to infection.
Biology of procalcitoninProcalcitonin, a propeptide of calcitonin, is normally produced in the C-cells of the thyroid gland [5,6]. A specific protease cleaves procalcitonin to calcitonin, katacalcin, and an N-terminal residue [5]. Normally all the procalcitonin is cleaved, and none released into the bloodstream. Procalcitonin levels are therefore very low (< 0.1 ng/ml) in healthy humans. However, during severe infections with systemic manifestations procalcitonin levels increase to over 100 ng/ml. Remarkably, the large amounts of procalcitonin produced during infections do not lead to an increase in plasma calcitonin levels or activity [7]. In contrast to the short half-life of calcitonin (10 min), procalcitonin has a long half-life of approximately 22±35 h in serum [8,9].During severe systemic infections procalcitonin is probably produced by extrathyroid tissues. Patients who have previously undergone total thyroidectomy can still produce high levels of procalcitonin during a severe infectious episode [7]. The exact site of procalcitonin production during sepsis is uncertain. In a hamster model of sepsis procalcitonin mRNA was found in numerous tissues [10]. Studies in our laboratory have implicated mononuclear leukocytes [11]; endotoxin and sepsis-related proinflammatory cytokines had pronounced stimulatory effects on procalcitonin mRNA expression in human mononuclear leukocytes when measured by the reverse-transcriptase polymerase chain reaction. End...