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. AIM: To determine whether different methods of saliva collection affect cortisol radioimmunoassay (RIA) performance. EXPERIMENTAL: 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). CONCLUSION: The use of cotton or polyester swabs for collection of saliva can result in spuriously high levels of cortisol when measured by RIA.

Lack of adult-type salivary cortisol circadian rhythm in hospitalized preterm infants.

BACKGROUND/AIMS: Knowledge of the presence or absence of cortisol (F) circadian rhythm in preterm infants is important for the interpretation of F measurements made in samples taken for both clinical and research purposes. Little is known about its emergence in very preterm infants. This study examines circadian rhythm in F secretion in hospitalized infants born before 30 weeks' gestation. DESIGN: Prospective longitudinal observational study. SUBJECTS: 11 infants admitted consecutively and born before 30 completed weeks of gestation. MEASUREMENTS: F was measured by highly specific radioimmunoassay on morning and evening saliva samples gathered at weekly intervals until discharged home. Circadian rhythm was defined as > or =40% reduction from morning to evening level. RESULTS: For all data, the median salivary F was 10.3 nmol/l (range <0.5-372.8). F levels were highest in the first 3 weeks of life. No infants displayed classical circadian rhythm for 4 weeks or more prior to being discharged from hospital. The other infants showed randomly distributed morning and evening F values with a trend in 4 infants towards periods of consistently higher evening than morning values. CONCLUSION: Adult-type F circadian rhythm is rarely evident in hospitalized preterm infants born before 30 weeks' gestation.