Despite advances in neonatal intensive care and significant gains in premature infant survival, necrotizing enterocolitis (NEC) remains one of the most significant complications of premature birth.1 As a greater number of preterm infants survive the early neonatal period, the preterm infant patient population at greatest risk of NEC increases.1-3 Infants who previously would have succumbed to other complications related to prematurity and low birth weight are surviving, yet often to develop gastrointestinal complications such as NEC. In short, NEC qualifies as one of the major unsolved problems of neonatal care.
Necrotizing enterocolitis is the most common gastrointestinal emergency in the neonatal intensive care unit, the most common cause of death in neonates undergoing surgery, and a major contributor to poor growth and neurodevelopmental outcome in children born preterm.2,4 Our knowledge of the disease pathogenesis, which includes an exaggerated inflammatory response,5 aberrant bacterial colonization,6,7 and an inability to repair damage to the intestinal mucosa,8 remains limited.1 Our limited understanding of NEC is made worse by the fact that the onset of the disease is often insidious yet progression rapid. Thus, neonatal clinicians need improved strategies to predict and ultimately prevent this gastrointestinal disease among preterm infants.
An improved ability to predict disease earlier in its pathogenesis and then tailor interventions to effectively prevent disease onset will revolutionize patient care and, in turn, improve human health. To predict disease, we need a detailed understanding of the combination of genetic and molecular events leading to disease pathogenesis, which will reveal candidate biomarkers of the specific disease. In addition, we need knowledge relevant to the clinical risk factors associated with disease onset. Thus, sensitive and specific biochemical predictors (ie, biomarkers such as inflammatory cytokines), as well as meaningful clinical risk factors, are important in developing effective disease prediction models for NEC. In this column, I have summarized some of the recent literature relevant to these disease prediction strategies for NEC.
BIOCHEMICAL PREDICTORS OF NEC IN PRETERM INFANTS
Several inflammatory cytokines have been implicated in the pathogenesis of NEC and have been studied as biomarkers of this disease.9,10 These lines of inquiry are important and have made a contribution to our understanding of the inflammatory response that is thought to play a role in NEC. For example, a prospective study has shown that infants who develop NEC requiring surgical intervention have a significantly higher serum concentration of the interleukin (IL)-6, IL-8, and IL-10 than their unaffected counterparts. When these inflammatory cytokines was analyzed together, infants who developed NEC were able to be clearly separated from controls. In contrast, IL-5, interferon [gamma], IL-4, and IL-2 showed slightly lower levels in the NEC cases than in controls.9
The NICHD Neonatal Research Network conducted a study that involved 104 extremely low-birth-weight infants with NEC and 893 unaffected controls cared for in 17 centers, with the goal of identifying inflammatory cytokines associated with NEC.10 Using a repeated-measures approach over the first 21 days following birth, lower blood TGF-[beta] and IL-2 levels and higher IL-8 levels were associated with NEC. In addition, this study found that infants who developed NEC had lower TGF-[beta] levels than controls, starting as soon as 1 day after birth and over the course of the first 3 postnatal weeks. The diagnosis of NEC was also associated with elevated IL-1[beta], IL-6, IL-8, IL-10, and C-reactive protein levels at the time of disease onset. In addition to these inflammatory cytokines, male sex and incidence of sepsis were associated with a diagnosis of NEC.10
These most recent studies add to a body of literature on inflammatory cytokines that may serve as systemic biomarkers of NEC. However, up- or downregulation of a specific cytokine or set of cytokines may not be fully attributed to NEC. An infant might exhibit these biologic events in response to any type of systemic inflammatory response (eg, sepsis). Thus, the ideal biomarker predicting NEC may be one that is specific to the gastrointestinal tract. In addition, the use of samples that may be collected via noninvasive means (ie, urine or stool samples) for biomarker assays has the advantage of a noninvasive approach that does not deplete the preterm infant of limited blood volume.
Recent work reporting on intestinal fatty acid-binding protein (i-FABP) as measured in urine11 may achieve the goal of identifying a biomarker specific to intestinal injury that is measurable in a non-serum-based sample. Intestinal fatty acid-binding protein is a protein found in the small intestinal enterocytes involved in the uptake and transport of polar lipids such as fatty acids from the small-bowel lumen.12,13 It has been associated with injury to the intestinal mucosa14 and injury common to inflammatory bowel diseases,15 including NEC.16-19 Intestinal fatty acid-binding protein has been successfully measured in serum17 and urine.16,19 In a prospective case-control study (n = 140), infants who developed NEC had significantly higher levels of i-FABP in their urine at both 3 and 7 days prior to disease onset. The difference between cases and controls was most pronounced in infants who developed the most mild and severe forms of the disease. Smaller differences were noted between infants with a moderate form of the disease and their matched controls, which may have been attributable to the finding that these infants were older when they received a diagnosis of the disease (ie, at a later time point following birth). This unexpected finding suggests that the maturity of the preterm infant bowel over time also plays a significant role in both the development of NEC and the measurement of inflammatory proteins among preterm infants.11
Calprotectin is a protein that has been shown to help prevent the growth of microorganisms, as well as induce programmed cell death via apoptosis. Because it is resistant to degradation and measurable in stool samples, it has been thought to be useful as a predictor of the inflammation common to gastrointestinal disease.20 Several investigators have explored the use of fecal calprotectin as a biochemical predictor of NEC in preterm infants. In recent case-control studies, infants with NEC have been shown to have significantly increased fecal calprotectin when compared with unaffected infants.20-22 In addition, fecal calprotectin has been shown to be useful in differentiating infants based on the severity of NEC diagnosis. Specifically, infants who develop more advanced stages of the disease have been shown to have the highest levels of fecal calprotectin at the time of disease onset.20
To date, the majority of studies that have evaluated both i-FABP and fecal calprotectin have relied on laboratory measurements that involve enzyme-linked immunosorbent assay (ELISA) kits, a technical approach that is time- and labor-intensive. It is exciting to see a recent report comparing rapid fecal calprotectin analysis via point-of-care testing with ELISA.23 In this report, like the findings from other studies, the level of fecal calprotectin was elevated in NEC cases when compared with controls. However, what was most interesting about this study was that the rapid measurement of fecal calprotectin via point-of-care testing was well correlated with the ELISA measurement of fecal calprotectin (r2 = 0.89).23 This study was the first to provide evidence that rapid measurement of a biomarker such as fecal calprotectin may be useful in the bedside diagnosis of NEC.
CLINICAL PREDICTORS OF NEC IN PRETERM INFANTS
Many epidemiologic based studies have explored clinical risk factors for NEC. However, one recent study has developed a novel clinical risk index for NEC that involved weighting individual risk factors to assess the composite odds of an individual infant developing NEC.24 This tool, GutCheckNEC, is designed to improve communication about an infant's risk of NEC and, in doing so, improve coordination of care throughout the neonatal intensive care unit stay.24
GutCheckNEC used an e-Delphi approach to identify risk factors for NEC. On the basis of this work, 9 independent risk factors were identified and then validated using logistic modeling and a large neonatal database for further derivation, validation, and calibration. These 9 risk factors included gestational age, history of packed red blood cell transfusion, unit NEC rate, late-onset sepsis, multiple infections, hypotension treated with inotropic medications, black or Hispanic race, outborn status, and metabolic acidosis. In addition, 2 protective factors were identified: human milk feeding on both days 7 and 14 of life, and administration of probiotics. Of all of these factors, unit NEC rate carried the most weight in the summed risk score, suggesting that a specific unit's overall practices were most relevant to the odds of an infant developing NEC. While further research and refinement of GutCheckNEC may be required, the recent study reported is an example of how large data sets comprising detailed clinical data can be used to develop disease prediction models that accurately predict disease onset in specific patient populations. This approach to better understanding risk for the purposes of early recognition, prediction, and prevention of disease is as important to identifying sensitive and specific biomarkers.
CONCLUSION: DISEASE PREDICTION RESULTS IN DISEASE PREVENTION
Why do we need to be so invested in developing and implementing more effective disease prediction strategies for NEC? Because with the implementation of disease prediction strategies such as the ones summarized here, we will be able to more effectively treat and prevent NEC. Nurses will be instrumental in developing specific patient-oriented interventions that are based on both biochemical and clinical predictors of NEC. These will likely include interventions that involve the adoption of a standardized feeding regimen that preferentially includes maternal breast milk, antimicrobial and histamine blocker stewardship, and ensuring acquisition of an optimal microbiome early in life, possibly via the administration of specific pre- or probiotics. Further research testing specific disease prediction strategies in the clinical setting is needed so that these may be implemented and the recognition of NEC may occur sooner in the course of the disease. In tandem with research on disease prediction, new treatment and prevention strategies for NEC may be identified and implemented, resulting in improved clinical outcomes for preterm infants and their families.
-Katherine E. Gregory, PhD, RN
Senior Nurse Scientist
Department of Pediatric Newborn Medicine
Department of Nursing
Brigham and Women's Hospital
Boston, Massachusetts
References