Reliability of Potential Pain Biomarkers in the Saliva of Healthy Subjects: Inter-Individual Differences and Intersession Variability

Abstract

AimSalivary cortisol, α-amylase (sAA), secretory IgA (sIgA), testosterone, and soluble fraction of receptor II of TNFα (sTNFαRII) could serve as objective pain measures, but the normal variability of these potential biomarkers is unknown.Patients & MethodsSaliva was collected with the passive secretion method from 34, pain-free subjects in two single samples at least 24 hours apart. Biomarker variation and intersession reliability were assessed with the intraclass correlation coefficient (ICC). Also, we calculated the within-subject standard deviation (Sw) and the reproducibility (2.77 × Sw) of intersession measures.ResultsSalivary cortisol, sAA, sIgA, testosterone, and sTNFαRII yielded the following ICCs: 0.53, 0.003, 0.88, 0.42 and 0.83, respectively. We found no statistically significant systematic differences between sessions in any biomarker except for testosterone, which showed a decrease on the second day (p<0.001). The reproducibility for salivary cortisol, sAA, sIgA, testosterone, and sTNFαRII were 0.46 ng/ml, 12.88 U/ml, 11.7 μg/ml, 14.54 pg/ml and 18.29 pg/ml, respectively. Cortisol, testosterone and TNFαRII measurement variability showed a positive correlation with the magnitude (p<0.002), but no relationship was found for sAA and sIgA.ConclusionsSalivary sIgA and sTNFαRII show a remarkable good reproducibility and, therefore, could be useful as pain biomarkers. When using the passive secretion method, intersession variations in salivary sIgA of more than 11.7 μg/ml may reflect true biomarker change. In the case of sTNFαRII this will depend of the magnitude. The estimates herein provided should help investigators and clinicians differentiate actual biomarker modification from measurement variability.

<p>Evaluation of Potential Pain Biomarkers in Saliva and Pain Perception After Corneal Advanced Surface Ablation Surgery</p>

“…5,32 Our group had analyzed the inter-individual differences and intersession variability in the saliva of healthy subjects for the current selected biomarkers. 15 We found significant variance in male and female testosterone, indicating that this hormone seems to be a poor salivary biomarker for pain. However, due to recent findings by Choi on the importance of considering the effects of testosterone on pain, we considered it necessary to include testosterone in this study.…”

“…The basal salivary concentrations of cortisol, sAA, sIgA, testosterone, and sTNFαRII were previously assessed by our group in a prospective study involving 34 pain-free healthy subjects in two single samples at least 24 hrs apart. 15 This research showed differences in potential biomarker concentrations between collections. Figure 1 shows biomarker concentration at four visits: V0, baseline; V1, pre-surgery; V2, 1 hr post-surgery, and V3, 72 hrs post-surgery.…”

“…That study did not find acceptable levels of reproducibility between two measurements. 15 Cortisol response to pain does not appear to be purely a function of the pain experience, because cortisol at V0 was significantly lower than at V1 and V2. It may be that other stress-related features, such as sympathetic activation, may be involved in the cortisol elevation detected.…”

“…The protocol on sample collection and analysis has been previously described in previous publications. 15,21 In brief, 32 subjects were instructed on how to carry out the saliva collection using the passive secretion method 21 over a 5-min period into a collection tube. The minimum amount of sample collected was at least 1 mL.…”

“…The findings suggested that salivary sIgA and sTNFαRII show remarkable reproducibility. 15 Owing to the controversy that exists regarding these substances as biomarkers of pain, and despite our previous findings, we decided to analyze all of them in patients with acute eye pain following Advanced Surface Ablation (ASA) surgery.…”