Western blotting is useful in the salivary diagnosis of Helicobacter pylori infection

L D Ballam¹, M A Mendall¹, M Asante¹, J Morris¹, D P Strachan², P H Whincup³ and D G Cook²

¹ GEMS Division, St George's Hospital Medical School, London SW17 0RE, UK
² Department of Public Health Sciences, St George's Hospital Medical School
³ Cardiovascular Research Group, Department of Primary Care and Population Sciences, University College and Royal Free Medical School, London NW3 2QG, UK

Correspondence to:
Dr Mendall, Mayday University Hospital, Mayday Road, Thornton Heath, Surrey CR7 7YE, UK email: mmendall{at}sghms.ac.uk

Background—The salivary diagnosis of Helicobacter pylori infection offers attractive possibilities for the epidemiological study of infection in children. Salivary enzyme linked immunosorbent assay (ELISA) is less reliable then serum ELISA, owing to variable transudation of immunoglobulin. In addition, children are more difficult to study because of lower specific serum antibody concentrations to H pylori. The performance of salivary western blotting in comparison with serum western blotting and serum ELISA was investigated in school children.

Subjects and methods—Paired serum and saliva specimens were obtained from 665 school children aged 9–11 in 10 British towns. All saliva and serum specimens were first analysed by ELISA; subsequently, western blotting of both specimens was performed on 31 and 34 specimens, respectively, to establish the criteria for positivity for western blotting. The remaining 121 specimens were then tested blindly and saliva was compared with the serum.

Results—The sensitivity and specificity of salivary ELISA in the 665 specimens was 32 of 50 (64%) and 530 of 691 (87%), respectively, when compared with serum ELISA. The western blotting validation was performed on 28 subjects with positive serum and positive salivary ELISA, 28 saliva positives with negative serum, 16 saliva negatives with positive serum, and 50 doubly negative subjects. Compared with serum western blots, the sensitivity and specificity of salivary western blots was 38 of 47 (81%) and 68 of 75 (91%), respectively. Using serum ELISA as the gold standard, the sensitivity and specificity were 32 of 44 (73%) and 72 of 78 (92%), respectively, the specificity being significantly higher than salivary ELISA (p < 0.001).

Conclusion—Salivary western blotting for IgG is useful in the diagnosis of H pylori infection and is superior to ELISA. It also permits the identification of pathogenic strains.

Key Words: Helicobacter pylori • western blotting • enzyme linked immunosorbent assay • salivary specimens

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