Objectives: Immunoglobulin A dominates mucosal surfaces and is a biomarker of interest in populations with a high disease burden. The objectives of this work are to describe an ELISA for IgA and test the stability of storage on filter paper for human milk and saliva collection to be used in remote field locations. Methods: A two‐site sandwich ELISA for IgA was developed. To test filter paper storage capabilities under field conditions, 248 matched whole and dried human milk filter paper samples and 251 matched whole and dried saliva samples were collected from northern Kenyan women. Whole samples were frozen in liquid nitrogen while dried samples were stored at ambient temperature for up to 8 weeks. Recovered dried IgA levels were compared to whole IgA levels and adjusted for time stored at ambient temperature. Results: The lower limit of quantification for this assay is 10.1 ng/ml. Linearity of dilution for human milk and saliva samples was excellent. High and low‐control coefficient of variation values across plates were 9.1 (341.8 ng/ml) and 9.4% (132.5 ng/ml). IgA was detected in all whole and dried samples. There is a moderate concordance between dried and whole samples ( R 2 = 0.62). There is a small but significant effect of time stored, with a loss of ∼1 μg/ml per day ( P = 0.0052). Conclusions: This IgA assay is a cost‐effective alternative to commercial secretory IgA kits. Human milk and saliva can be stored on filter paper for up to 8 weeks. Am. J. Hum. Biol., 2011. © 2011 Wiley‐Liss, Inc
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