Background. Nasal lavage is a common method for obtaining samples of nasopharyngeal (NP) secretions. The major disadvantage of this method is that the degree of dilution in the collected specimens is unknown and varies between subjects, which may severely distort the results. Several proteins have been used to correct for this varying dilution, but there are no reports comparing the suitability of different proteins for this purpose. An optimal standardization protein should show a minimal variation between different individuals and remain stable in the course of time. We compared the suitability of total protein, albumin, and secretory IgA (sIgA) for standardization by determining the variation in the levels of these proteins in NP secretions from children with upper respiratory infection (URI).

Methods. NP aspirate specimens from 52 children with URI and acute otitis media were studied. Specimens were obtained at the time of diagnosis of otitis and 2-3 days later. Total protein content in the samples was measured by the bicinchoninic acid protein assay, and albumin and sIgA levels were determined by enzyme immunoassay. To avoid the impact of extreme values, comparisons were based on the 10th and 90th percentile values for each protein.

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