Fecal lactoferrin as a marker of fecal leukocytes.

We read with interest the report of Guerrant et al. (1). It was stated that the fecal lactoferrin assay may be a useful diagnostic tool in the evaluation of patients with acute diarrhea syndrome (ADS), offering some advantages over microscopic examination for fecal leukocytes. We would like to comment on this and report data from a study carried out in Chile in which fecal lactoferrin was measured as described elsewhere (1) by using anti-human lactoferrin antibody (L-232; Sigma). Titers above 1:60 were considered positive. In agreement with previous reports (1,2) showing that lactoferrin is present in human milk (1 g/liter), colostrum (7g/liter), and cow milk (0.1 g/liter), we found lactoferrinpositive reactions at dilutions of up to 1:105 in milk samples from humans and cows and pasteurized liquid and infant formula (NAN and NIDO; Nestle). The antibody was shown to cross-react with bovine lactoferrin, but only with human milk did it consistently show a more coarse pattern of agglutination. The fecal lactoferrin assay was evaluated with 63 pediatric patients with ADS and 25 healthy infants. Stool samples were collected for fecal lactoferrin, fecal leukocytes, and microbiological analysis (bacterial and parasitic enteric pathogens and rotavirus). The type of milk received 48 h prior to sample collection was also recorded. Among the 25 control infants, all were negative for fecal leukocytes, 8 breast-fed infants were positive for fecal lactoferrin (5 of them at titers over 1:540), and 17 infants fed other kinds of milk were negative for fecal lactoferrin. The presence of lactoferrin in the stools appeared to correlate strictly with breast-feeding. Since 10 of 63 patients with ADS had been breast-fed, they were excluded from further analysis. Of 53 patients with ADS, 28 patients were positive for fecal lactoferrin, 15 of them were also positive for fecal leukocytes, and 22 produced samples that had identifiable enteric pathogens (enteropathogenic Escherichia coli [EPEC], 11; rotavirus, 5; Cryptosporidium spp., 3; Campylobacter jejuni, 1; Entamoeba histolytica, 1; and Shigella flexneri, 1). Twenty-five patients with ADS were negative for fecal lactoferrin, 23 of them were negative for fecal leukocytes and only 6 had an identifiable pathogen (EPEC, 2; rotavirus, 3; and Shigella sonnei, 1). These results suggest that fecal lactoferrin could be a more sensitive test than fecal leukocytes for the evaluation of patients with ADS, but one should keep in mind the possibility of false positives with breast-fed infants, even when high titers of fecal lactoferrin are detected.