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Pediatric Clinical Chemistry |
1 Department of Pediatrics, and 2 Center of Epidemiology and Biostatistics, Prince of Wales Hospital, The Chinese University of Hong Kong, Hong Kong Special Administrative Region.
aAddress correspondence to this author at: Department of Pediatrics, Level 6, Clinical Sciences Bldg, Prince of Wales Hospital, Shatin, New Territories, Hong Kong, SAR. Fax 852-2636-0020; e-mail pakcheungng{at}cuhk.edu.hk.
| Abstract |
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Methods: We measured a panel of chemokines and cytokines at 0 and 24 h after clinical presentation in VLBW infants with suspected infection requiring full sepsis screening. The chemokines measured were interleukin (IL)-8, interferon-
-inducible protein-10 (IP-10), monokine induced by interferon-
, monocyte chemoattractant protein-1, and regulated upon activation normal T-cell expressed and secreted (RANTES), and the cytokines were IL-6, IL-10, and tumor necrosis factor-
.
Results: Of 195 episodes of suspected clinical sepsis investigated, 62 were culture-confirmed septicemia or necrotizing enterocolitis (28 of these infants developed DIC), 22 were culture-negative clinical infections, and 111 involved noninfected episodes. All studied inflammatory mediators except RANTES showed significantly greater up-regulation in culture-positive infected infants than in noninfected infants at 0 and 24 h, whereas RANTES showed significant down-regulation. The model that used plasma IL-10 (>208 ng/L), IL-6 (>168 ng/L), and RANTES (<3110 ng/L) at 0 h had sensitivity, specificity, and positive and negative predictive values of 100%, 97%, 85%, and 100%, respectively, for identifying infected patients who subsequently developed DIC.
Conclusions: IL-10, IL-6, and RANTES measured at clinical presentation sensitively and accurately predicted the development of DIC in severely infected infants. This information could be vital for early and effective treatment of neonatal sepsis.
| Introduction |
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Much basic and clinical research has been focused on the inflammatory cascade in sepsis and the use of newly discovered inflammatory mediators for early diagnosis and outcome prediction. It is now known that the acute inflammatory reaction can exert dual influences on patients with sepsis (7)(8). Chemokines and proinflammatory cytokines are essential for host defense against microbial infection, but excessive influx of activated leukocytes coupled with exaggerated production of potent proinflammatory mediators can contribute to deleterious consequences, leading to widespread small-vessel damage, multiorgan dysfunction, and death (8)(9)(10). More importantly, antiinflammatory cytokines such as interleukin (IL)-10 have counterregulatory properties that can down-regulate the release and effect of proinflammatory mediators (11)(12)(13). Recent advances in flow cytometry have facilitated the study of important inflammatory mediators with minimal volumes of blood. This prospective study was aimed (a) to investigate in VLBW infants with septicemia and necrotizing enterocolitis (NEC) the profile of key chemokines and cytokines, including the chemokines IL-8, interferon-
inducible protein-10 (IP-10), monokine induced by interferon-
(MIG), monocyte chemoattractant protein-1 (MCP-1), and regulated upon activation normal T cell expressed and secreted (RANTES), and the pro- and antiinflammatory cytokines IL-6, tumor necrosis factor-
(TNF-
), and IL-10; (b) to quantitatively compare the magnitude of inflammatory response in severely infected infants who subsequently developed DIC with the response in less seriously infected infants without DIC; and (c) to use the measurement of inflammatory mediators to predict the development of sepsis-induced DIC at the onset of clinical presentation of infection. Early identification of infants with severe infection and DIC could enable neonatologists to pay special attention to patients who are most at risk for serious complications and adverse outcomes. These chemokines were chosen because they are chemoattractants of major leukocyte subsets involved in the infection process (14)(15)(16). Furthermore, we chose a set of pro- and antiinflammatory cytokines because the delicate balance between these 2 types of mediators has been shown to influence the prognosis and outcome of infection.
| Patients and Methods |
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methods
All infants were recruited at the time of clinical presentation during the initial evaluation (0 h) for suspected clinical sepsis. The study was approved by the Research Ethics Committee of The Chinese University of Hong Kong. Written informed consent was obtained from the parents for all patients. The signs and symptoms of clinical sepsis and the infection screening procedure have been described in detail in our previous studies (5)(17) (see Text 1 in the Data Supplement that accompanies the online version of this article at http://www.clinchem.org/content/vol52/issue6/). The first blood sample for inflammatory mediator measurements was taken at the time of the initial sepsis evaluation (0 h), and a second sample was obtained 24 h after the onset for monitoring the clinical progress. This schedule of blood sampling coincided exactly with our unit policy for serial blood count and C-reactive protein (CRP) measurements. Intravenous antibiotics, including vancomycin and a third-generation cephalosporin or an aminoglycoside, were started immediately after the sepsis screening and collection of the first set of blood samples (5)(17), and the antimicrobial treatment was intended to be given for a full course of at least 7 days in infected infants.
Three categories of infective episodes were defined prospectively as follows: Group 1, the infected group, included infants with sepsis episodes that had been confirmed as microbial culturepositive sepsis, including septicemia, meningitis, peritonitis, systemic fungal infection, or NEC [stage II or above in Bells classification with or without positive bacterial/fungal culture (18)]. However, cases with positive microbial cultures from superficial body sites were likely to be colonization and were not classified as true infections. A subgroup of severely infected infants who developed DIC and had increased serum D-dimer concentration >1.0 mg/L (reference interval, 0.51.0 mg/L), thrombocytopenia (<100 x 109 cells/L), and deranged coagulation with prolonged activated partial thromboplastin time [>120 s; reference interval, 26.240.1 s (19)] was also identified. Group 2, the clinically infected culture-negative group, included infants with sepsis episodes having at least 3 clinical signs and symptoms suggestive of clinical sepsis or chest radiographic features suggestive of pneumonia, and serial (at least 2) serum CRP concentrations persistently >10 mg/L. These episodes were classified as true infections based on their strong and persistent clinical signs of sepsis, and in these cases, clinical improvement bore a close temporal relationship to the normalization of serial CRP measurements. Group 3, the noninfected group, included infants who met the initial screening criteria for suspected clinical sepsis but were subsequently classified as noninfected, with antibiotics stopped early, 2496 h after initiation of treatment. During the classification procedure, all recruited cases were reviewed by an experienced neonatologist and a pediatric radiologist who were blinded to the identities of the patients and the results of chemokine and cytokine measurements. The duration of antibiotic treatment was never used as the sole parameter to decide whether an infant was infected.
measurements of cytokines, chemokines, and crp
Blood samples were collected from indwelling arterial lines or by venipuncture into tubes; the tubes were immersed in ice and immediately transported to the laboratory for processing. Plasma was separated by centrifugation (1900g for 5 min) at 4 °C and stored in 200-µL aliquots at 80 °C until analysis. All clinical specimens, including those from our earlier study (17), were stored and processed identically to ensure uniformity of measurements. None of the samples was thawed before analysis. Serum CRP was measured by a turbidity assay against controls, as specified by the manufacturer (Behring Diagnostics Inc.). A panel of cytokines (IL-6, IL-10, and TNF-
) and a panel of chemokines (IL-8, IP-10, MIG, MCP-1, and RANTES) were quantified by use of Cytometric Bead Array Kits (BD Biosciences Pharmingen) with flow cytometry. The detection limits of the assays were 2.5, 3.3, 3.7, 0.2, 2.8, 2.5, 2.7, and 1.0 ng/L, respectively. The intraassay CVs, obtained by measurement of 10 replicates of plasma samples containing low, medium, and high concentrations of inflammatory mediators, were 5.1%11%, 5.0%11%, and 3.3%12%, respectively (for details see Text 1 in the online Data Supplement).
statistical analysis
We used the KruskalWallis test and
2 test to compare the demographic data of patients and the plasma concentrations of different inflammatory mediators in the infected (group 1), clinically infected culture-negative (group 2), and noninfected (group 3) groups, and the MannWhitney U-test to compare chemokine and cytokine concentrations in the subgroup analysis. The significance level of the latter test was adjusted by Bonferroni correction for multiple comparisons (P = 0.017 for comparison of 3 groups). In addition, we used the CART model (20) (see Text 1 in the online Data Supplement) to identify those mediators and criteria best used for predicting sepsis-induced DIC at the onset of infection (0 h). All statistical tests were performed with SPSS for Windows (Release 11; SPSS Inc.) and S-Plus 2000 (Release 3; MathSoft Inc.).
| Results |
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The details of causative organisms and clinical pathologies of infected episodes in group 1 are summarized in Table 1
. In this group, 28 infants developed DIC. In group 2, no microorganism was isolated from blood or cerebrospinal fluid specimens from 22 infants with presumed clinical infection. The clinical diagnoses of 111 noninfected cases (group 3) are summarized in Table 1 of the online Data Supplement. None of the cases in groups 2 and 3 developed DIC.
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overall analysis
The comparison of plasma/serum inflammatory mediator concentrations among the groups is summarized in Table 2
(for detailed results, see Table 2 in the online Data Supplement). Plasma/serum IL-6, IL-8, IL-10, IP-10, MIG, MCP-1, TNF-
, and CRP concentrations were significantly higher in group 1 than in group 3 infants at 0 h (P <0.001) and 24 h (P <0.01), whereas plasma RANTES concentrations were significantly lower at both time points (P <0.001). In addition, plasma/serum inflammatory mediator concentrations of group 2 infants were intermediately increased compared with the concentrations of groups 1 and 3. For most inflammatory mediators, except IL-8 and RANTES, the chemokine and cytokine concentrations of group 2 infants were significantly higher than those of group 3 infants at one or both time points.
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subgroup analysis
We compared infected cases with and without DIC (Tables 3
and 4
; for detailed results, see Tables 3 and 4 of the online Data Supplement). In the DIC group, the majority of cases (n = 20; 72%) were attributable to gram-negative/fungal septicemia (n = 17; 61%), complicated NEC with small-bowel perforation (n = 2; 7%), and serious gram-positive infection such as coagulase-negative staphylococcus sepsis with liver abscess formation (n = 1; 4%). In contrast, the non-DIC group comprised mainly infants with infection (n = 29; 85%) attributable to coagulase-negative staphylococcus septicemia (n = 19; 56%) or uncomplicated NEC (n = 10; 29%). All studied inflammatory mediators, with the exception of the 2 non-glutamic acid-leucine-arginine (non-ELR) chemokines IP-10 and MIG, were significantly higher in infected episodes associated with DIC than in those without DIC, but RANTES showed a significantly opposite trend (Table 3
; for detailed results, see Table 3 in the online Data Supplement). In addition, the proinflammatory mediator/antiinflammatory cytokine ratios were assessed in both DIC and non-DIC episodes. All ratios except IL-8/IL-10 and TNF-
/IL-10 were significantly lower in the DIC group, and only the IL-6/IL-10 ratio showed a significantly reversed trend (Table 4
; for detailed results, see Table 4 in the online Data Supplement). This observation was principally attributable to a substantial increase in plasma IL-10 concentration, which was increased out of proportion compared with other proinflammatory cytokines (with the exception of IL-6) and chemokines.
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We used the CART model with these inflammatory mediators to predict the development of DIC at the very first signs of sepsis (i.e., at the initial stage of clinical presentation and sepsis evaluation at 0 h). The use of plasma IL-10 concentration >208 ng/L correctly identified 23 of 28 (82%) infants with DIC. The sequential use of plasma IL-6 concentrations >168 ng/L and plasma RANTES concentrations <3110 ng/L further identified the remainder of the DIC patients and minimized misclassification of non-DIC cases (Fig. 1
). The sensitivity, specificity, and positive and negative predictive values (95% confidence intervals shown in parentheses) of this model were 100 (97.7100)%, 97 (93.299.0)%, 85 (68.194.9)%, and 100 (97.9100)%, respectively.
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| Discussion |
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The relatively large number of culture-confirmed sepsis and NEC cases in the current study enabled the analysis of important subgroups of infected patients. Plasma IL-6, IL-8, IL-10, MCP-1, and TNF-
concentrations were significantly increased in severely infected infants with DIC compared with less seriously infected infants without DIC, whereas plasma RANTES was significantly lower in the former subgroup. However, concentrations of 2 non-ELR chemokines, IP-10 and MIG, which act specifically on the CXCR-3 receptor, were not significantly different among the groups (Table 3
), suggesting that they were not strongly influenced by the severity of sepsis. In adult patients with sepsis-induced acute respiratory distress syndrome, mortality rates were higher in those with markedly increased concentrations of IL-8 in the bronchoalveolar lavage fluid (35). Similarly, high blood concentrations of IL-8(23)(24), MCP-1(25), IL-6(8), and IL-10 (33)(34) and a high IL-10/TNF-
ratio (36) were positively correlated with the severity of the infective process and the occurrence of septic shock and multiorgan failure and, in general, signified a poorer prognosis. Furthermore, in our study, the clinically infected culture-negative group (group 2) had intermediate increases in chemokine and cytokine concentrations compared with groups 1 and 3 (Table 2
; for detailed results see Table 2 of the online Data Supplement). These patients were probably less severely infected and had bacterial loads below the detection thresholds of laboratory tests. Plasma RANTES concentrations decreased significantly in preterm infants with severe sepsis and DIC. A similar phenomenon has also been observed in adult patients (8)(27) and might be related to the thrombocytopenic state associated with DIC, as platelets have been found to be a rich source of RANTES (8)(37). Platelet surfaces express CD40 costimulatory molecules (38)(39), which interact with the CD154 counter-receptor on activated T lymphocytes, thereby triggering the release of preformed RANTES (40). Although the immunologic profile in preterm infants indicated that most of the studied chemokines and pro- and antiinflammatory cytokines were up-regulated and involved in the sepsis-induced inflammatory cascade, the specific patterns and magnitudes of expression in different subgroups reflected their individual roles in modulating the progress of the inflammatory process in response to the severity of infection.
The most prominent feature observed in this study was the intense induction of IL-6 and IL-10 by infection signals such as endotoxins and bacteria or their products in the sickest infants. Median plasma IL-6 and IL-10 concentrations in patients with DIC at 0 h were at least 60- and 12-fold higher, respectively, than the corresponding concentrations in group 1 infants without DIC (Table 3
). These characteristics rendered the 2 inflammatory mediators particularly useful in differentiating severely ill infants from less seriously infected patients at an early stage (29)(31)(33)(34). Measurement of IL-10 (>208 ng/L) enabled identification of 82% (23 of 28) of infected infants who subsequently developed DIC. The concomitant use of IL-6 (>168 ng/L) enabled identification of all DIC infants but led to misclassification of 17 non-DIC cases. Addition of RANTES (<3110 ng/L) greatly improved the specificity and positive predictive value of the diagnostic model by decreasing the number of misclassified non-DIC cases to 5 (Fig. 1
). The overall sensitivity and specificity of this model were 100% and 97%, respectively. Comparing the analysis of the CART model with a model using CRP results, the most commonly used infection marker, we found that serum CRP concentrations >15.5 mg/L at 0 h had a sensitivity of 79% and specificity of 78% for identifying DIC cases. Thus, we have shown that the measurement of key cytokines/chemokines in as little as 0.10 mL of plasma could sensitively and accurately identify septic infants with DIC at the onset of clinical presentation (0 h). In contrast, with the use of conventional clinical and laboratory criteria, DIC was diagnosed in all 28 infants 3.7 days (88 h) after the onset of clinical presentation. The use of cytokine and chemokine measurements could greatly facilitate identification of severely infected DIC cases and targeting of specific treatment for the sickest infants at a very early stage of infection.
Four infected infants with DIC died during the acute septic process. Although in all cases the chemokine and cytokine concentrations were abnormal and could be identified by our CART model, their concentrations at 0 h varied widely among patients (ranges: IL-10, 311703 ng/L; IL-6, 187591 658 ng/L; RANTES, 365-2032 ng/L), thus rendering the prediction of fatal cases difficult. The large variation in plasma concentrations of chemokines and cytokines in the infants who died could have been related to the specific underlying pathologies or the different stages of infection at which blood samples were collected, because most of these mediators were only transiently increased in the early phase. This transient increase could be an intrinsic weakness of many of the chemokines and cytokines being used as diagnostic markers (6). Ideally, the inflammatory mediator or diagnostic marker should remain increased for an adequate time period, e.g., 24 h, to minimize the inaccuracy of the test attributable to timing of blood sampling (6). Thus, this study was specifically designed to monitor 2 time points (0 and 24 h) in an attempt to identify the most appropriate mediators at a clinically relevant timing for predicting DIC.
In summary, our findings suggest that all studied chemokines and cytokines except RANTES were markedly up-regulated in VLBW infants with septicemia and NEC, whereas RANTES was significantly down-regulated, indicating that preterm infants are capable of eliciting strong chemotactic and pro- and antiinflammatory responses to invading pathogens. Infants with sepsis episodes that eventually progressed to DIC had significantly greater changes in plasma inflammatory mediator concentrations compared with infants with milder infections without DIC. More importantly, IL-10, IL-6, and RANTES measurements could be used to sensitively and reliably predict the development of DIC in septic infants at the onset of clinical presentation. Thus, quantitative measurements of these inflammatory mediators could assist neonatologists in predicting the severity of infection and DIC, thereby identifying seriously ill infants who are most in need of urgent treatment and targeting those who are most at risk of adverse outcomes. Although assays for most chemokines and cytokines are not currently being used for identifying neonatal sepsis or for predicting the severity and outcome of infection, we believe that assays for these mediators will be used routinely once they become fully automated (6). The next step is to conduct a randomized controlled study to confirm the clinical usefulness of this CART model and to investigate whether accurate prediction of DIC at the onset of sepsis presentation could lead to improved parental counseling, clinical management, and treatment outcomes of severely infected infants.
| Acknowledgments |
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| Footnotes |
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-inducible protein-10; MIG, monokine induced by interferon-
; MCP-1, monocyte chemoattractant protein-1; RANTES, regulated upon activation normal T cell expressed and secreted; TNF-
, tumor necrosis factor-
; CRP, C-reactive protein; and ELR, glutamic acid-leucine-arginine. | References |
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B. Pediatr Res 2003;54:382-386.[CrossRef][Medline]
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