Bioavailable + Free Testost.

Test ID: 

704108

CPT code:

84403, 84402 (x2)

Synonyms:

Free Testosterone, Direct

Testosterone, Free, Direct

Clinical Use:

Evaluate hirsutism and masculinization in women; evaluate testicular function in clinical states where the testosterone binding proteins may be altered (obesity, cirrhosis, thyroid disorders). See individual test descriptions for more information. A pediatric reference interval has not been established for the direct free testosterone test.

Test Information:

The concentration of free testosterone is very low, typically <2% of the total testosterone concentration. In most men and women, >50% of total circulating testosterone is bound to sex hormone-binding globulin, SHBG, and most of the rest is bound to albumin. Routinely available assay methods used to measure total testosterone are not sensitive enough to accurately quantitate the free testosterone fraction directly. Free testosterone is estimated in this test by a direct, analogue immunoassay method. This assay uses a labeled testosterone analogue that has a low binding affinity for both SHBG and albumin but is bound by antitestosterone antibody used in the assay. Since the analogue is unbound in the plasma, it competes with free testosterone for binding sites on an antitestosterone antibody that is immobilized on the surface of the microtiter plate well.

Specimen Type:

Serum

Requested Volume: 

0.5 mL

Minimum Volume: 

0.3 mL

Container Type: 

Red-top tube or gel-barrier tube

Collection:

If a red-top tube is used, transfer separated serum to a plastic transport tube.

Storage Instructions:

Room temperature

Stability Requirements:

Rejection Criteria

Plasma specimen; gross lipemia (may yield erroneously high free testosterone results)