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Testosterone Free Blood Test, Mass Spectrometry/Equilibrium Dialysis (Endocrine Sciences)

A Testosterone Free Blood Test, Mass Spectrometry/Equilibrium Dialysis is helpful in assessing testicular function in prepubescent hypogonadal males and in managing hirsutism, virilization in females.

Sample Report

Test Code: 500726

Also Known As:

Methodology: Testosterone: high-pressure liquid chromatography (HPLC)/tandem mass spectrometry; free testosterone: equilibrium dialysis

Preparation: No special preparation required.

Test Results: 7-8 days. May take longer based on weather, holiday or lab delays.


Free testosterone is the fraction of total testosterone that is not bound to circulating proteins. The free fraction is available to diffuse into target cells to interact with receptors or enzymes. The concentration of free testosterone is low relative to total testosterone, typically <3% of the total testosterone concentration. Total circulating testosterone is bound to sex hormone-binding globulin (SHBG) or albumin. Measurement of total and free testosterone is key in diagnosis of androgen excess or deficiency. Free testosterone is best measured by equilibrium dialysis, while total testosterone is measured by HPLC with tandem mass spectrometry.

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