Testosterone (Free), Serum (Equilibrium Ultrafiltration) With Total Testosterone
| Testosterone (Free), Serum (Equilibrium Ultrafiltration) With Total Testosterone | | | |
| Number | | 081786 |
| CPT | | 84402; 84403 |
| Related Information | | Follicle-Stimulating Hormone (FSH), Serum Luteinizing Hormone (LH), Serum |
| Synonyms | | Testosterone, Free/Total, Serum |
| Test Includes | | Total, free, and percent free testosterone |
| Special Instructions | | State patient's age and sex on the request form. |
| Specimen | | Serum |
| Volume | | 1.8 mL |
| Minimum Volume | | 1 mL (Note: This volume does not allow for repeat testing.) |
| Container | | Red-top tube or gel-barrier tube |
| Collection | | Separate serum from cells. If a red-top tube is used, transfer separated serum to a plastic transport tube. |
| Storage Instructions | | Refrigerate |
| Causes for Rejection | | Gross lipemia; recently administered isotopes; plasma specimen |
| Reference Interval | | See table.1
| Age | Male
(ng/dL) | Female
(ng/dL) | | Free Testosterone | | Cord blood | 0.50-2.20 | 0.40-1.60 | | 1-15 d | 0.15-3.10 | 0.05-0.25 | | 1-2 mo | 0.33-0.80 | 0.01-0.13 | | 3-5 mo | 0.07-1.40 | 0.03-0.11 | | 6-7 mo | 0.04-0.48 | 0.02-0.06 | | 6-9 y | 0.01-0.32 | 0.01-0.09 | | 10-11 y | 0.06-0.57 | 0.10-0.52 | | 12-14 y | 0.14-15.60 | 0.10-0.52 | | 15-17 y | 8.00-15.90 | 0.10-0.52 | | Adults | 5.00-21.00 | 0.10-0.85 | | Percentage of Total Testosterone | | Cord blood | 2.00-4.40 | 2.00-3.90 | | 1-15 d | 0.90-1.70 | 0.80-1.50 | | 1-2 mo | 0.40-0.80 | 0.40-1.10 | | 3-5 mo | 0.40-1.10 | 0.50-1.00 | | 6-7 mo | 0.40-1.00 | 0.50-0.80 | | 6-9 y | 0.90-1.70 | 0.90-1.40 | | 10-11 y | 1.00-1.90 | 1.00-1.90 | | 12-14 y | 1.30-3.00 | 1.00-1.90 | | 15-17 y | 1.80-2.70 | 1.00-1.90 | | Adults | 1.50-4.20 | 0.50-2.80 |
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| 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) |
| Methodology | | Free: equilibrium ultrafiltration; total: immunochemiluminometric assay (ICMA) |
| Additional 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.2 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 profile by an indirect method, equilibrium ultrafiltration. Tritiated testosterone is added to the sample and allowed to come to equilibrium with testosterone in the serum at physiological temperature.3,4 The amount of the added radiolabeled testosterone must be low enough to ensure that the addition will not significantly increase the total testosterone concentration. Once equilibrium is achieved, the free testosterone is separated from the bound by filtration through a membrane by centrifugal ultrafiltration.5 The radioactivity of the protein-free ultrafiltrate is measured and used to calculate the percent free testosterone. The concentration of free testosterone is then calculated by multiplying the percent free testosterone by the total testosterone concentration. |
| Footnotes | | - Tietz NW, ed, Clinical Guide to Laboratory Tests, 3rd ed, Philadelphia, PA: WB Saunders Co, 1995, 578.
- Wheeler MJ, “The Determination of Bioavailable Testosterone,” Ann Clin Biochem, 1995, 32(Pt 4):345-57 (review).
- Klee GG and Heser DW, “Techniques to Measure Testosterone in the Elderly,” Mayo Clin Proc, 2000, 75(Suppl):S19-S25.
- Gronowski AM and Landau-Levine M, “Reproductive Endocrine Function,” Burtis CA and Ashwood ER, eds, Tietz Textbook of Clinical Chemistry, 3rd ed, Philadelphia, PA: WB Saunders Co, 1999, 1601-41.
- Vlahos I, MacMahon W, and Sgoutas D, “An Improved Ultrafiltration Method for Determining Free Testosterone in Serum,” Clin Chem, 1982, 28(11):2286-91
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