Test Catalog

Test ID: TTFB    
Testosterone, Total, Bioavailable, and Free, Serum

Method Description Describes how the test is performed and provides a method-specific reference

Total Testosterone:

Deuterated stable isotope (d3-testosterone) is added to a 0.2-mL serum sample as an internal standard. Protein is precipitated from the mixture by the addition of acetonitrile. The testosterone and internal standard are extracted from the resulting supernatant by an online extraction utilizing high-throughput liquid chromatography (HTLC). This is followed by conventional liquid chromatography and analysis on a tandem mass spectrometer equipped with a heated nebulizer ion source.(Wang C, Catlin DH, Demers LM, et al: Measurement of total testosterone in adult men: comparison of current laboratory methods versus liquid chromatography-tandem mass spectrometry. J Clin Endocrinol Metab. 2004;89:534-543; Taieb J, Mathian B, Millot F, et al: Testosterone measured by 10 immunoassays and by isotope-dilution gas chromatography-mass spectrometry in sera from 116 men, women, and children. Clin Chem. 2003;49:1381-1395)


Free Testosterone:

This method is based on equilibrium dialysis in which free-labeled testosterone is allowed to pass through a semipermeable membrane, whereas testosterone bound to the sex hormone-binding globulin (SHBG) remains inside the dialysis tubing. After dialysis, radioactivity is measured both inside and outside the tubing; the free testosterone results are expressed as a percentage of total testosterone. The resulting percentage is multiplied by the total testosterone concentration obtained by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and an absolute free testosterone value is obtained.(Vermeulen A, Stoica T, Verdonck L: The apparent free testosterone concentration, an index of androgenicity. J Clin Endocrinol Metab. 1971;33:759-767; Bammann BL, Coulam C, Jiang NS: Total and free testosterone during pregnancy. Am J Obstet Gynecol. 1980;137:293-298)


Bioavailable Testosterone:

The method is based on the differential precipitation of SHBG by ammonium sulfate following equilibration of the serum specimen and tracer amounts of tritium-labeled testosterone. The results are expressed as the percent of testosterone free or albumin bound (not precipitated with SHBG) compared to an albumin standard. The product of this percentage and the total testosterone measurement is the total bioavailable testosterone.(Wheeler MJ: The determination of bioavailable testosterone. Ann Clin Biochem. 1995;32:345-357)

PDF Report Indicates whether the report includes an additional document with charts, images or other enriched information


Day(s) Performed Outlines the days the test is performed. This field reflects the day that the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time before the test is performed. Some tests are listed as continuously performed, which means that assays are performed multiple times during the day.

Monday through Saturday

Report Available The interval of time (receipt of sample at Mayo Clinic Laboratories to results available) taking into account standard setup days and weekends. The first day is the time that it typically takes for a result to be available. The last day is the time it might take, accounting for any necessary repeated testing.

3 to 5 days

Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded

2 weeks

Performing Laboratory Location Indicates the location of the laboratory that performs the test