Contamination of human gingival crevicular fluid by plaque and saliva.

Dental plaque and saliva are both possible contaminants of gingival crevicular fluid (GCF). Plaque samples from 12 sites in four subjects who had allowed plaque to accumulate for 24-48 h were quantified using the Plaque Index and then transferred to filter paper strips for fluid volume determination using the Periotron 6000. The mean volume of fluid for plaque scores of 0 was 0.02 (+/- 0.01) microliter, whereas for plaque scores of 3 the mean volume was 0.15 (+/- 0.07) microliters. In a clinical study, GCF samples, from 19/184 subjects (10.4%) were assessed as contaminated or suspected to be contaminated with saliva, but only 28/1740 strips (1.6%) were placed in these categories of contamination. An assay to confirm salivary contamination was established, using an immunochemical, double-antibody method with sheep anti-human salivary alpha-amylase followed by peroxidase-conjugated rabbit anti-sheep immunoglobulin. The detection threshold of the assay was 7.5 ng of alpha-amylase, which represents approx. 15-25 nl of saliva. The assay was evaluated on 90 GCF samples categorized as 'known' (n = 16), 'suspected' (n = 16), or 'not' contaminated (n = 58) with saliva; 81.25, 50-61.5 and 5.2-8.6%, respectively, were positive for salivary alpha-amylase. In some GCF samples salivary contamination was in excess of 50%. It was concluded that GCF samples seen to be contaminated with saliva should be discarded, whereas samples considered free from contamination may be used with confidence. Samples suspected of contamination may require an alpha-amylase assay before further analysis.