Endocrine Abstracts

Background

There is a need to develop a highly sensitive and reliable immunoassay method for the determination of testosterone concentrations both in children and adults. Testosterone in blood is largely bound to proteins (sex hormone binding globulin and albumin). The unbound fraction of testosterone is considered to be the biologically active hormone which correlates more closely with the physiologically effective level of this hormone. It is postulated that the free fraction or unbound fraction interacts with specific receptors in the target cells to exert their hormonal effects.

As saliva is a natural ultrafiltrate of blood, only the free fraction of the hormone freely diffuse into the saliva. Saliva sampling offers a non-invasive , stress-free and painless method for the long-term or repeated sequential sampling schedules (such as monitoring steroid replacement in children with congenital adrenal hyperplasia) and enable collection time to be more controlled which is central for baseline testing due to its circadian rhythm.

Method

The salivary testosterone assay has been developed from a currently used in-house method at the Department of Clinical Biochemistry at Glasgow Royal Infirmary. The key to the success of this assay is the inclusion of an antibody raised against testoterone-3-carboxymethyloxime in sheep which binds to testosterone with high affinity. The antibody is very specific with the only major cross-reactant being dihyrotestosterone (12%). The sensitivity of this assay is 25pmol/L and the interassay and intraassay coefficient variation are 15% and 9% respectively.

Reference Ranges

Salivary testosterone concentration for adult men (n=99) ranged from 216-1370pmol/L (mean 404 pmol/L) and for adult women (n=73) ranged from <25 to 149pmol/L (mean 88pmol/L). For children, in girls aged 10-16 years, concentration ranged from <25-134pmol/L and in boys aged <10 years old, concentration ranged from <25-44pmol/L and for boys aged between of 10-16 years, concentration ranged from <25 -1340pmol/L.