Abstract
Background: Despite the use of saliva with enzyme immunoassay (EIA) methods validated for use with blood to measure interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-[alpha]), there has been limited validation of saliva as a matrix for EIA of IL-6 and TNF-[alpha].
Objectives: The study aims were to (a) validate one vendor's commercially available EIAs for detecting IL-6 and TNF-[alpha] in saliva as an alternative matrix to blood and (b) test the long-term stability of EIA detection of IL-6 and TNF-[alpha] after 12-month storage of saliva and plasma.
Methods: Spike and recovery and linearity experiments were performed. Concentrations of IL-6 and TNF-[alpha] in saliva and plasma from 20 healthy adult volunteers (6 men and 14 women) were correlated; the assays were repeated 12 months later.
Results: Spike and recovery and linearity performance was adequate for salivary IL-6: intra-assay percentage coefficient of variation, less than or equal to 8.4%; sensitivity, 0.11 pg/ml; mean recoveries, 81% in spiked saliva and 110% in spiked controls; and linearity, r = .995. The association between IL-6 in saliva and plasma was moderate and significant (p = .04). Spike and recovery and linearity performance was inadequate for TNF-[alpha]: intra-assay coefficient of variation, 10.8%; sensitivity, 2.3 pg/ml; mean recoveries, 44% in spiked saliva and 92% in spiked controls; and linearity, r = .950. The association between TNF-[alpha] in saliva and plasma was low and insignificant. Plasma and saliva IL-6 levels were significantly higher (p < .0001), and plasma and saliva TNF-[alpha] levels were significantly lower (p < .0001) after 12-month storage of specimens.
Discussion: We concluded that (a) saliva can be used to assess IL-6, but not TNF-[alpha], with an EIA validated for use with blood and (b) 12-month storage of plasma and saliva significantly changes the assay results. Validation of other EIAs would expand assay options for investigators.