Measurement of immunoglobulin A in saliva by particle-enhanced nephelometric immunoassay: sample collection, limits of quantitation, precision, stability and reference range

This version was published on 1 September 2009

Ann Clin Biochem 2009;46:401-406
© 2009 Association for Clinical Biochemistry


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Original Articles

Christine K Booth1,
Dan B Dwyer2,
Paul F Pacque2 and
Madeleine J Ball2

1 Human Protection & Performance Division, DSTO-Scottsdale, Tasmania;
2 School of Human Life Sciences, University of Tasmania, Launceston, Tasmania, Australia

Corresponding author: Christine Booth PhD, P.O. Box 147, Scottsdale 7260 Tasmania, Australia. Email: christine.booth{at}

Background: Total immunoglobulin A in saliva (s-IgA) is normally assayedusing an enzyme-linked immunosorbent assay. We have investigatedmethodological issues relating to the use of particle-enhancednephelometric immunoassay (PENIA) to measure s-IgA in wholeunstimulated saliva and determine its reference range.

Methods: Whole unstimulated resting saliva was collected to determinesample stability (temperature, time, effect of a protease inhibitor),limit of quantitation (LOQ), assay precision and analyticalvariation. The reference range for 134 healthy adults was determined.

Results: Linearity was excellent (4–10.3 mg L–1, P < 0.001; R2 = 0.997) and without significant bias (mean of –0.7%). The lowest intra- and inter-analytical coefficients of variation were 1.8% and 7.5% and LOQ was 1.4 mg L–1. The concentration of s-IgA is stable at room temperature for up to 6 h, at 4°C for 48 h, at –4°C for two weeks and at –80°C for up to 1.3 yr. There is no evidence that a protease inhibitor increases the stability or that repeated freeze–thawing cycles degrade sample quality. The reference ranges for s-IgA concentration, s-IgA secretion, s-IgA:albumin and s-IgA:osmolality were 15.9–414.5 mg L–1, 7.2–234.9 µg min–1, 0.4–19 and 0.6–8.9, respectively.

Conclusion: Automated PENIA assay of s-IgA is precise and accurate. Highstability of collected saliva samples and the ease and speedof the assay make this an ideal method for use in athletic andmilitary training situations. The convenience of measuring albuminand IgA on the same analytical platform adds to the practicabilityof the test.

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