Richard H. Snider

Procalcitonin assay in systemic inflammation, infection, and sepsis : Clinical utility and limitations

Objective:The use of procalcitonin (ProCT) as a marker of several clinical conditions, in particular, systemic inflammation, infection, and sepsis, will be clarified, and its current limitations will be delineated. In particular, the need for a more sensitive assay will be emphasized. For these purposes, the medical literature comprising clinical studies pertaining to the measurement of serum ProCT in various clinical settings was examined. Data Source and Selection:A PubMed search (1965 through November 2007) was conducted, including manual cross-referencing. Pertinent complete publications were obtained using the MeSH terms procalcitonin, C-reactive protein, sepsis, and biological markers. Textbook chapters were also read and extracted. Data Extraction and Synthesis:Available clinical and other patient data from these sources were reviewed, including any data relating to precipitating factors, clinical findings, associated illnesses, and patient outcome. Published data concerning sensitivity, specificity, and reproducibility of ProCT assays were reviewed. Conclusions:Based on available data, the measurement of serum ProCT has definite utility as a marker of severe systemic inflammation, infection, and sepsis. However, publications concerning its diagnostic and prognostic utility are contradictory. In addition, patient characteristics and clinical settings vary markedly, and the data have been difficult to interpret and often extrapolated inappropriately to clinical usage. Furthermore, attempts at meta-analyses are greatly compromised by the divergent circumstances of reported studies and by the sparsity and different timing of the ProCT assays. Although a high ProCT commonly occurs in infection, it is also elevated in some noninfectious conditions. Thus, the test is not a specific indicator of either infection or sepsis. Moreover, in any individual patient, the precipitating cause of an illness, the clinical milieu, and complicating conditions may render tenuous any reliable estimations of severity or prognosis. It also is apparent that even a febrile septic patient with documented bacteremia may not necessarily have a serum ProCT that is elevated above the limit of functional sensitivity of the assay. In this regard, the most commonly applied assay (i.e., LUMItest) is insufficiently sensitive to detect potentially important mild elevations or trends. Clinical studies with a more sensitive ProCT assay that is capable of rapid and practicable day-to-day monitoring are needed and shortly may be available. In addition, investigations showing that ProCT and its related peptides may have mediator relevance point to the need for evaluating therapeutic countermeasures and studying the pathophysiologic effect of hyperprocalcitonemia in serious infection and sepsis.

Mortality is increased by procalcitonin and decreased by an antiserum reactive to procalcitonin in experimental sepsis.

OBJECTIVES Procalcitonin (ProCT), the precursor to the calcitonin hormone, is abnormally increased in experimental and clinical systemic inflammation, including sepsis. Initially, we investigated the effects of supraphysiologic amounts of ProCT administered to animals with septic peritonitis. Subsequently, we evaluated the efficacy of prophylactic and therapeutic immune blockade of ProCT in this lethal model of sepsis. DESIGN Prospective, experimental, controlled study. SETTING Animal research laboratory approved by the American Association for the Accreditation of Laboratory Animal Care at a Veterans Affairs Medical Center. SUBJECTS Young male Golden Syrian hamsters, weighing 90 to 120 g. INTERVENTIONS In the first study, serum ProCT concentrations were measured in animals at 0, 3, 6, 12, and 24 hrs after induction of sepsis by intraperitoneal implantation of pellets containing Escherichia coli (5 x 10(8) colony-forming units/pellet). In the second study, with mortality as the end point, 30 microg/kg of isolated, purified human ProCT in 10% hamster serum (experimental) or an equal volume of 10% hamster serum (control) were administered intravenously at the time of the E. coli peritoneal implantation. In the third study, experimental animals received intraperitoneal injections of a multiregion-specific goat antiserum reactive to hamster ProCT 1 hr before and 24 hrs after E. coli implantation, while control animals received nonimmune goat serum at the same time points. In the final study, the same antiserum was administered in five divided doses during the 24 hrs after the insertion of E. coli. MEASUREMENTS AND MAIN RESULTS In the initial study, ProCT concentrations were increased shortly after induction of sepsis and peaked at 12 hrs. Administration of exogenous ProCT to septic animals significantly increased mortality compared with control animals (93% vs. 43%, p=.02). Prophylactic blockade of ProCT almost completely protected the animals from the lethal effects of sepsis: the 102-hr mortality rate in the experimental group was 6% compared with 62% in the control group (p < .003). In the therapeutic trial, the 102-hr mortality rate was 54% in experimental animals compared with 82% in control animals (p < .045). CONCLUSIONS These results demonstrate that increased ProCT exacerbates mortality in experimental sepsis, whereas neutralization of ProCT increases survival. Thus, ProCT, in addition to being an important marker of severity of systemic inflammation and mortality, is an integral part of the inflammatory process and directly affects the outcome.

Procalcitonin in sepsis and systemic inflammation: a harmful biomarker and a therapeutic target

The worldwide yearly mortality from sepsis is substantial, greater than that of cancer of the lung and breast combined. Moreover, its incidence is increasing, and its response to therapy has not appreciably improved. In this condition, the secretion of procalcitonin (ProCT), the prohormone of calcitonin, is augmented greatly, attaining levels up to thousands of fold of normal. This hypersecretion emanates from multiple tissues throughout the body that are not traditionally viewed as being endocrine. The serum values of ProCT correlate with the severity of sepsis; they recede with its improvement and worsen with exacerbation. Accordingly, as highlighted in this review, serum ProCT has become useful as a biomarker to assist in the diagnosis of sepsis, as well as related infectious or inflammatory conditions. It is also a useful monitor of the clinical course and prognosis, and sensitive and specific assays have been developed for its measurement. Moreover, it has been demonstrated that the administration of ProCT to septic animals greatly increases mortality, and several toxic effects of ProCT have been elucidated by in vitro experimental studies. Antibodies have been developed that neutralize the harmful effects of ProCT, and their use markedly decreases the symptomatology and mortality of animals that harbour a highly virulent sepsis analogous to that occurring in humans. This therapy is facilitated by the long duration of serum ProCT elevation, which allows for a broad window of therapeutic opportunity. An experimental groundwork has been established that suggests a potential applicability of such therapy in septic humans.

Calcitonin in extrathyroidal tissues of man.

Prior studies have demonstrated detectable immunoreactive calcitonin in the serum and urine of totally thyroidectomized humans, suggesting that the hormone may be secreted by extrathyroidal tissues. Accordingly, a study of the immunoreactive calcitonin content of human tissues was undertaken, utilizing autopsy material from 23 patients. Significant amounts of calcitonin were found in many extrathyroidal tissues, ranging up to 40 ng/g wet weight. The hormone was detectable with two antibodies having different region specificities for calcitonin. Gel filtration and subsequent radioimmunoassay demonstrated that extrathyroidal tissue has calcitonin fractions of the same molecular size and charge characteristics as do the serum and thyroid. The finding of large amounts of extrathyroidal calcitonin may explain why thyroidectomy in man is not accompanied by marked changes in calcium metabolism.

Disordered calcium homeostasis of sepsis: association with calcitonin precursors

Hypocalcemia and increased serum levels of calcitonin precursors are common in critically ill patients, especially in those with sepsis. We investigated calcium homeostasis in such patients.

Interleukin-6, interleukin-8, and a rapid and sensitive assay for calcitonin precursors for the determination of bacterial sepsis in febrile neutropenic children.

Objective: Children with cancer often develop febrile illnesses after cytotoxic chemotherapy. Determining which children have serious bacterial infections in this vulnerable period would be valuable. We evaluated the ability of a rapid and sensitive assay for the concentration of calcitonin precursors (CTpr) as a sensitive diagnostic marker for bacterial sepsis in febrile, neutropenic children and determined the utility of measuring cytokines to improve the predictive value of this approach. Design: Prospective cohort study. Setting: Academic children’s hospital. Patients: Fifty-six children (aged 5 months to 17 yrs) with a known malignancy who presented with fever and neutropenia. Interventions: Serial blood samples were obtained (admission, 24 hrs, and 48 hrs), and concentrations of CTpr, interleukin-6, and interleukin-8 were determined. Demographic and laboratory data from the patients were collected from the medical record. Measurements and Main Results: Sixteen (29%) of the children met the criteria for bacterial sepsis. Plasma levels of CTpr and interleukin-8, but not interleukin-6, were increased at all time points in children with sepsis compared with those without sepsis. CTpr at 24 and 48 hrs after admission were reliable markers for sepsis (area under the curve = 0.92 and 0.908, respectively). Logistic regression using CTpr at 24 hrs in addition to interleukin-8 at 48 hrs produced the best-fit models associated with sepsis. Using cutoff values of CTpr >500 pg/mL and interleukin-8 >20 pg/mL produced a screening test for sepsis with 94% sensitivity and 90% specificity. Conclusions: Our data show the utility of a rapid and sensitive assay for CTpr combined with interleukin-8 as a highly sensitive and specific diagnostic marker of bacterial sepsis in febrile, neutropenic children. The use of these markers as a clinical tool may allow for better prognostication for clinicians and may eventually lead to more targeted therapies for this heterogeneous population.

Effect of classic heatstroke on serum procalcitonin.

OBJECTIVE Procalcitonin, the precursor peptide of calcitonin, has been shown to be a serum marker of the severity and mortality of several systemic inflammatory response syndromes. This study addressed the correlation of serum procalcitonin with the course of classic (nonexertional) heatstroke. DESIGN Serum samples were collected prospectively every 6 hrs for 24 hrs. SETTING Heatstroke treatment unit, Makkah, Saudi Arabia. PATIENTS A total of 25 patients were admitted during the annual Hajj pilgrimage in 1994. Ten patients evaluated in the same treatment center with minor illnesses and without pyrexia served as controls. INTERVENTIONS Patients were cooled according to an established evaporation method. MEASUREMENTS AND MAIN RESULTS Standard critical care parameters including continuous rectal temperature. A rapid immunochemical assay for serum procalcitonin was utilized. The mean serum procalcitonin was elevated 20-fold on admission in patients with heatstroke compared with controls (p < .011). The procalcitonin concentration subsequently increased to a plateau by 6 hrs and remained increased at 24 hrs, compared with the admission level (p < .0001). In this study, 77% of the patients with heatstroke survived. A subgroup analysis demonstrated that the patients who survived had a significantly higher procalcitonin concentration than those patients who died of heatstroke; a procalcitonin concentration of >0.5 ng/mL (>0.15 nmol/L) at 6 hrs predicted survival (p = .02). CONCLUSION Classic heatstroke is associated with increased concentrations of serum procalcitonin, particularly among survivors. Further studies are required to elucidate the source and action(s) of procalcitonin as well as its relationship to cytokine activation.

Procalcitonin and proinflammatory cytokine interactions in sepsis.

Immunoneutralization of procalcitonin (ProCT), a putative mediator of sepsis, has been shown to increase survival in an animal model of sepsis. To better understand the role that ProCT plays in the sepsis cascade, we studied the relationship of this hormone to the proximal proinflammatory mediators, IL-1beta and TNFalpha. Hamsters were made septic by i.p. implantation of Escherichia coli-impregnated agar pellets. A time line study of serum IL-beta, TNFalpha, and ProCT levels showed that the increase in the cytokines was transient and less than 2-fold over baseline, whereas ProCT increased >100-fold by 12 h and remains elevated through 24 h. TNFalpha (400 microg/kg) was injected into healthy animals, inducing an elevation in ProCT that was 25-fold greater than controls. ProCT (30 microg/kg) was given to healthy and septic animals. In healthy animals, there was no significant elevation in serum IL-1beta or TNFalpha levels. In septic animals, IL-1beta was modestly blunted at 3 h but not at 12 h, and there was no change in TNFalpha levels. ProCT did not initiate or enhance IL-1beta or TNFalpha expression; however, the massive and sustained elevation of this hormone seen in sepsis can be induced by the proximal cytokine, TNFalpha. This study suggests that ProCT is a secondary mediator that might augment and amplify but does not initiate the septic response. Immunoneutralization of ProCT may prove to be an important clinical strategy, in view of its sustained elevation and the difficulty in initiating therapy for sepsis during the early phases of illness.

Effects of Anti‐inflammatory Agents on Serum Levels of Calcitonin Precursors during Human Experimental Endotoxemia

Calcitonin precursor (CTpr) levels are both markers and mediators of inflammation. The duration of their elevation after intravenous endotoxin challenge and the effects of anti-inflammatory therapies were studied in 52 subjects. CTpr levels maximized at 24 h in all subjects. At 7 days (n=4), after levels of acute-phase cytokines and C-reactive protein had normalized, CTpr levels remained 2-4-fold above baseline levels. The elimination half-life of CTpr levels ranged from 26.9 to 45.7 h. At 24 h, endotoxin and ibuprofen (compared with endotoxin alone) increased CTpr levels approximately 2-fold (P=.03), whereas soluble tumor necrosis factor receptor blunted the increase in CTpr levels by 2-3-fold (P=.0015). However, soluble interleukin-1 receptor failed to alter the increase in CTpr levels. Thus, the fact that anti-inflammatory agents may alter CTpr levels resulting from a single stimulus must be considered when CTpr is used as a clinical marker. Of importance, this study reveals that anti-inflammatory agents may modulate the CTpr level, which is a potential toxic mediator of inflammation.

Late immunoneutralization of procalcitonin arrests the progression of lethal porcine sepsis.

BACKGROUND Procalcitonin (ProCT) is becoming increasingly recognized as a mediator as well as a marker of sepsis. Serum ProCT concentrations rise soon after induction of sepsis and remain elevated over a prolonged period of time. In contrast, many pro-inflammatory cytokines, e.g., tumor necrosis factor alpha (TNF-alpha) and interleukin-1 beta (IL-1beta), rise and decline early in the course of sepsis. Researchers have improved survival in animal models of sepsis by prophylactically blocking IL-1beta and TNF-alpha with immunotherapy, but therapeutic treatment has been less successful in clinical trials. We hypothesized that the sustained elevation of ProCT in the serum would allow for effective therapeutic immunoneutralization of this peptide late in the course of sepsis. METHODS Lethal polymicrobial sepsis was induced in 10 castrated, male Yorkshire pigs by intraabdominal spillage of cecal contents (1 gm/kg) and intraabdominal instillation of 2 x 10(11) cfu of a toxigenic strain of E. coli (O18:K1:H7). The treated group (n = 5) received an intravenous infusion of purified rabbit antiserum to the aminoterminus of porcine ProCT. The control group (n = 5) received nonreactive, purified rabbit IgG. The purified antiserum was infused to all animals 3 h after the induction of sepsis, at which time very severe physiologic dysfunction was manifest, and many of the animals appeared to be preterminal. Physiologic and metabolic parameters were measured until death or for 15 h after induction of sepsis, at which time all surviving animals were euthanized. RESULTS Therapeutic immunoneutralization of serum ProCT improved most measured physiologic and metabolic parameters in septic pigs. Specifically, there was a significant increase in mean arterial pressure, urine output and cardiac index in all animals treated with ProCT antibody. Serum creatinine was significantly lower in treated animals. Although acidosis was not as severe in treated animals, as indicated by higher pH values and lower lactate concentrations, these results did not achieve statistical significance. Significantly, 11 h after the induction of sepsis there was 100% mortality in the control group while only one animal in the treated group expired. CONCLUSION The prolonged elevation of ProCT concentrations in sepsis allows neutralization of this peptide to be effective during the course of this disorder. These findings suggest that immunoneutralization of ProCT may be a useful treatment in clinical situations where sepsis is already fully established.