Saliva collection method affects predictability of serum cortisol

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Abstract

Background

Measurement of cortisol is of particular importance for early diagnosis of adrenocorticotropic dysfunction and therapeutic monitoring. Saliva samples clearly present an easily manageable, non-invasive and anytime practicable assessment method of glucocorticoid production. The aims of the present study were to compare salivary cortisol collection method “Salivette” versus “passive drool”, salivary cortisol concentrations with calculated free serum cortisol (FSC) and total serum cortisol (TSC) and the prediction of serum cortisol by salivary cortisol.

Methods

Saliva samples were collected by Sarstedt-Salivette® and by passive drooling into plastic tubes. Salivary cortisol, TSC measurements and calculation of FSC concentrations as well were carried out simultaneously in 10 healthy volunteers on two consecutive days at six definite points of time (08.00–23.00).

Results

Significant differences of salivary cortisol concentrations dependent on the saliva collection method (F-test 6.45; p = 0.0317) and points of times were found (F-test 41.19; p < 0.0001). Stronger overall correlation was observed in Salivette-salivary cortisol vs. TSC (r = 0.813) and FSC (r = 0.836) as compared to passive drooling. Specifically, more significant correlations were established in Salivettes vs. TSC (8/12 points of time, 66.7%) and FSC (8/12 points of time, 66.7%) than in passive drooling (TSC: 1/12 points of time, 8.3% and FSC: 2/12 points of time, 16.7%). Importantly, cortisol in Salivettes was a better predictor for FSC and TSC than passive drooling.

Conclusions

Our data indicate that salivary cortisol measurement with Salivettes is a reliable prediction method of total and calculated free serum cortisol levels. Moreover, it is a convenient method for saliva collection, handling and laboratory processing.

Introduction

Cortisol is an important adrenal biomarker which can be measured in serum, urine or saliva. In addition to the assessment of adrenocorticotropic function and therapeutic monitoring it is an important analyte in stress research. In clinical routine, total serum cortisol (TSC) is the standard measurement when evaluating basal or diurnal cortisol levels.

Because it represents the amount of free and thus biologically active cortisol [1], [2], salivary cortisol measurement has become increasingly important. Additionally this technique is a non-invasive method that is not painful like drawing blood and, therefore, does not provide an additional stressor. The most common methods for saliva collection are via cotton swab (Salivette®, Sarstedt, Nümbrecht, Germany) and via passive drooling into a plastic tube.

Several studies indicate that the sampling method has an impact on the amount of measured cortisol in saliva [3], [4], [5], [6], [7]. All the same no parallel comparison of these salivary cortisol measurements with total serum cortisol and calculated free serum cortisol (FSC) values has been performed. Before this background it was our aim to compare both saliva collection methods concerning the amount of measured cortisol and to set them into relation to FSC and TSC as reference values.

Section snippets

Study participants and design

Ten healthy volunteers (5 males, 5 females, mean age 31.7 years, range 22–46 years) participated in the study. None of the volunteers received oral medication (e.g. glucocorticoids, thyreoid hormones, and insulin) sensitizing the adrenocorticotropic function or had a history of taking these medications. Furthermore, none of the participants had an acute concurrent inflammation/infection (e.g. oral or pharyngeal) as determined by measurement of C-reactive Protein (CrP) as biomarker for

Comparison of salivary cortisol collection method “Salivette” versus “passive drool”

Continuously lower mean salivary cortisol concentrations in Salivettes than in plastic tubes were found independent of point of time or different day (data not shown).

The three-way repeated measures ANOVA showed statistically significant differences of salivary cortisol concentrations between the two saliva collection methods (F = 6.45; p = 0.032 and strong significant differences at six different points of time (F = 41.19; p < 0.0001) (Table 1), respectively. There was no significant difference

Discussion

Our study is the first to compare different saliva collection methods and to explore the relationship between salivary cortisol and total as well as calculated free serum cortisol concentrations with respect to the two collection devices used. The main finding of our study is that despite a lower cortisol concentration in Salivettes, salivary cortisol in Salivettes was the better predictor for TSC and FSC than salivary cortisol in plastic tubes. Salivettes were also the preferred method of

Acknowledgements

We thank Leo Heuts (Central Laboratory, RWTH–University Hospital Aachen) for the expert technical assistance and Diagnostic Systems Laboratories (Sinsheim, Germany) for providing us with reagents for the study.

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