The data collected in this large pediatric population demonstrate that FLA levels correlate with disease activity (assessed prospectively) determined by previously validated disease activity indices. Our data also suggest that FLA levels may be elevated in patients who are clinically well but subsequently experience a flare in disease activity. The data are consistent with findings reported in previous adult series (10,13,16,21).
The acute and chronic active inflammation observed in patients with IBD is characterized by an influx of activated neutrophils into and across the mucosal lining, resulting in the formation of crypt abscesses in the intestinal lumen. Clinicians have used the identification of fecal leukocytes as a way to differentiate patients with inflammatory (ie, invasive bacterial infection, IBD) from those with noninflammatory (ie, viral, toxigenic) diarrheal illness. Fecal leukocyte analysis, however, is limited by its lack of sensitivity, its dependence on a fresh stool sample, and the skill of the laboratory technician (41–44). By contrast, measuring FLA, a product of activated neutrophils (43), is a simple and reliable method of detecting and quantifying inflammatory cells in the stool of patients whose conditions are being evaluated for IBD (10,13,16,21).
Several factors support the inclusion of FLA levels in the diagnosis and interval assessment of IBS. First, because lactoferrin can be measured in feces, it is likely to be a more direct measure of intestinal inflammation than are serum markers such as ESR (as demonstrated in the present study) that reflect systemic inflammation. Second, because FLA measurements are collected noninvasively, they are especially attractive for use in pediatric patients, in whom phlebotomy is both anxiety provoking and technically difficult. Third, the relative ease of sample collection and the prospect of monitoring FLA in samples collected and then sent through the mail (similarly to samples for ova and parasites examination) or collected at a patient's bedside, makes FLA measurements especially well suited for serial assay in the same patient over time. Finally, quantitative FLA levels are easily and reliably measured in the stool by use of a commercially available diagnostic test that has been cleared by the US Food and Drug Administration (10,17,42).
It should be noted that there are limitations to the use of FLA measurements and other stool-based assays that clinicians must keep in mind when applying surrogate markers in the diagnosis and treatment of their patients with IBD. It may be more difficult for parents to collect samples from less cooperative pediatric patients. In addition, elevated FLA levels indicate intestinal inflammation that may be caused by infections and by clinical flares in IBD activity. Therefore, clinicians need to consider obtaining stool cultures from patients presenting with rectal bleeding or symptoms of colitis.
Most fecal markers studied to date, including α-1-antitrypsin, elastase, lysozyme, esterase, and myeloperoxidase, have not been fully validated for clinical use, and it remains unclear how closely their levels reflect the presence or extent of intestinal inflammation (14,45). By contrast, fecal levels of calprotectin, another neutrophil-derived protein, seem to reflect active intestinal inflammation in patients with IBD (10,45,46). Both FLA and calprotectin show similar results for patient groups with intestinal inflammation. However, within the normal population, a significant number of people with baseline lactoferrin levels have elevated fecal calprotectin levels (47). Fecal calprotectin levels are significantly higher in patient populations with IBD than in patients with IBS, and they seem to be correlated with clinical and endoscopic disease activity in patients with UC and, to a lesser degree, with CD (40,46,48–53). However, the clinical application of fecal calprotectin as a screening tool in pediatric and adult populations has been hindered by an apparent lack of consensus with respect to normative values and units of measurement in published reports (49,54,55). Large-scale comparative trials in pediatric patients are needed to evaluate the relative utility of these biomarkers in clinical practice.
We further evaluated the potential utility of FLA measurements in predicting patients who are at risk for disease flares by comparing the short-term (2-month) clinical outcome in patients with inactive disease at the time of specimen collection. We found that FLA levels were significantly increased in patients who then experienced flares within 2 months of sample collection in comparison with patients who remained in remission. Although our sample size was relatively small, the results were significantly different, and they raise the possibility that elevations in FLA may presage clinical flares. This question is being addressed in a multicenter study evaluating the utility of serial lactoferrin measurements in pediatric and adult patients with active and inactive IBD. Our data further demonstrate that quantitative FLA measurements are highly correlated with commonly used biochemical metrics of inflammation, including ESR, hematocrit, Alb, and Plt count.
An inherent weakness of our study, and perhaps all studies evaluating the use of surrogate markers in the assessment of patients with IBD, is the lack of an accepted gold standard of disease activity against which to measure their validity. Although endoscopic and histological assessments are generally accepted as definitive benchmarks, their application is limited by their cost, invasive nature, and potential interrater reliability. As such, we were unable to correlate FLA levels with disease location and severity in this study. Similarly, we were not able to correlate FLA measurements, clinical activity, and disease location in subgroups of patients with primarily small or large bowel IBD. In our study population 5 of 62 (8%) patients with UC had disease limited to the left colon, and no patients had isolated proctitis, which was consistent with previous reports of disease distribution in pediatric patients (1). Patients with CD limited to the large or small intestine were similarly rare (4/79 and 13/79, respectively). Future studies using simultaneous FLA and endoscopic assessment will be necessary to fully define the degree to which FLA is influenced by the extent and localization of endoscopic inflammation.
The development of valid, noninvasive, and readily obtainable surrogate markers of intestinal disease activity will contribute significantly to patient care. In addition, the application of surrogate markers, such as FLA, could play an important role in pharmaceutical trials by reducing both the cost and the length of time necessary to determine the effects of novel anti-inflammatory therapies and by limiting the need for more invasive diagnostic studies. Further studies are needed to define how to optimize the inclusion of FLA measurements into the prospective management of IBD in children and adults.
The authors thank the Children's Hospital Clinical Research Program and General Clinical Research Center (MO1 RR-02172) for assistance with this study, Dr. Richard J. Grand for his time and effort in revising this manuscript, and the Children's Hospital Center for Inflammatory Bowel Disease, the Wolpow Family Fund, and the community of patients and providers for their support in completing this clinical study.
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