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

Clinical Use

Use

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.1-3 Free testosterone is estimated in this profile using these recommended techniques.

Special Instructions

Not provided.

Limitations

The method is specifically recommended for women, children, and hypogonadal men, and it may not be suitable for other populations. It is crucial that the samples are handled as advised to prevent deterioration, affecting the accuracy of the results due to degradation or changes in the specimen during handling or storage.

Test Details

Methodology

Mass Spectrometry

Biomarkers

Free Testosterone

Analyte

Total Testosterone

Concentration / Level • Quantitative (Continuous) (e.g., copies/mL, % expression)

% Free Testosterone (Dialysis)

Concentration / Level • Quantitative (Continuous) (e.g., copies/mL, % expression)

Free Testosterone, Serum

Concentration / Level • Quantitative (Continuous) (e.g., copies/mL, % expression)

LOINC Codes

Order Codes

2991-8 - Testost Free SerPl-mCnc

Result Codes

2986-8 - Testost SerPl-mCnc
15432-8 - Testost Free MFr SerPl
2991-8 - Testost Free SerPl-mCnc

Result Turnaround Time

6-10 days

Specimen

Serum

Volume

2 mL

Minimum Volume

1 mL

Container

Gel-barrier tube or red-top tube

Collection Instructions

Serum must be separated from cells within 45 minutes of venipuncture. Send serum in a plastic transport tube. Submit separate frozen specimens for each test requested to avoid delays.