A re-investigation of saliva collection procedures that highlights the risk of potential positive interference in cortisol immunoassay.
BACKGROUND
The use of saliva for measurement of cortisol permits non-invasive study of adrenal function, but collection can be technically difficult, particularly in small infants. Saliva collection can be assisted by citric acid to increase saliva flow, or by the use of cotton or polyester swabs in the mouth.


OBJECTIVE
To determine whether different methods of saliva collection affect cortisol radioimmunoassay (RIA) performance.


METHODS
Cortisol was measured in saliva collected from 16 adults using intra-oral cotton swabs or polyester swabs, compared with saliva dribbled directly into a pot either alone (plain saliva) or after citric acid had been placed on the tongue. An in-house RIA, without prior extraction, was used to measure cortisol with an encapsulated sheep antibody.


RESULTS
Mean (median) salivary cortisol was 10.9 (10.5) nmol L(-1) in plain saliva, 10.4 (8.4) nmol L(-1) in citric acid stimulated saliva; 25.3 (25.1) nmol L(-1) in saliva collected on cotton swabs, and 27.9 (27.3) nmol L(-1) collected on polyester swabs. Cortisol in saliva collected using citric acid was not significantly different from plain saliva (p=0.997), but cortisol in saliva collected using cotton and polyester swabs was significantly higher than that of plain saliva (p<0.01).


CONCLUSIONS
The use of cotton or polyester swabs for collection of saliva can result in spuriously high levels of cortisol when measured by RIA.
Kidd
Susan
S
Department of Child Life and Health, University of Edinburgh, 20 Sylvan Place, Edinburgh EH9, UK.
Midgley
Paula
P
Lone
Nazir
N
Wallace
A Michael
AM
Nicol
Mary
M
Smith
John
J
McIntosh
Neil
N
D000328:Adult; D016477:Artifacts; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000032:analysis*; D007118:Immunoassay; D008297:Male; D012306:Risk; D012463:Saliva / Q000737:chemistry; D013048:Specimen Handling / Q000379:methods* / Q000592:standards
D006854:Hydrocortisone