Test Details
Methodology
Free: equilibrium ultrafiltration; total: liquid chromatography/tandem mass spectrometry (LC/MS-MS)
Result Turnaround Time
4 - 6 days
Use
Evaluate hirsutism and masculinization in women; evaluate testicular function in clinical states in which the testosterone-binding proteins may be altered (obesity, cirrhosis, thyroid disorders)
Special Instructions
State patient's age and sex on the test request form.
Specimen Requirements
Limitations
This test was developed and its performance characteristics determined by Labcorp. It has not been cleared or approved by the Food and Drug Administration.
Custom 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.1 Routinely available assay methods used to measure total testosterone are not sensitive enough to quantitate accurately 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.2,3 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 testosterone by filtration through a membrane by centrifugal ultrafiltration.4 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.
Specimen
Serum
Volume
2.2 mL
Minimum Volume
1.8 mL (Note: This volume does not allow for repeat testing.)
Container
Red-top tube or gel-barrier tube
Storage Instructions
Room temperature
Causes for Rejection
Hemolyzed sample; icteric sample; gross lipemia; recently administered isotopes; plasma specimen
Collection Instructions
Serum should be transferred from cells within one hour of collection and transferred to a plastic transport tube.
Stability Requirements
Temperature | Period |
|---|---|
Room temperature | 7 days |
Refrigerated | 7 days |
Frozen | 5.58 years |
Freeze/thaw cycles | Stable x9 |
Reference Range
See table.1
Free Testosterone | ||
|---|---|---|
Age | Male (ng/dL) | Female (ng/dL) |
Cord blood | 0.50−2.20 | 0.40−1.60 |
1 to 15 d | 0.15−3.10 | 0.05−0.25 |
1 to 2 m | 0.33−0.80 | 0.01−0.13 |
3 to 5 m | 0.07−1.40 | 0.03−0.11 |
6 to 7 m | 0.04−0.48 | 0.02−0.06 |
6 to 9 y | 0.01−0.32 | 0.01−0.09 |
10 to 11 y | 0.06−0.57 | 0.10−0.52 |
12 to 14 y | 0.14−15.60 | 0.10−0.52 |
15 to 17 y | 8.00−15.90 | 0.10−0.52 |
Adults | 5.00−21.00 | 0.10−0.85 |
Percentage of Total Testosterone | ||
Age | Male (%) | Female (%) |
Cord blood | 2.00−4.40 | 2.00−3.90 |
1 to 15 d | 0.90−1.70 | 0.80−1.50 |
1 to 2 m | 0.40−0.80 | 0.40−1.10 |
3 to 5 m | 0.40−1.10 | 0.50−1.00 |
6 to 7 m | 0.40−1.00 | 0.50−0.80 |
6 to 9 y | 0.90−1.70 | 0.90−1.40 |
10 to 11 y | 1.00−1.90 | 1.00−1.90 |
12 to 14 y | 1.30−3.00 | 1.00−1.90 |
15 to 17 y | 1.80−2.70 | 1.00−1.90 |
Adults | 1.50−4.20 | 0.50−2.80 |
Footnotes
LOINC® Map
| Order Code | Order Code Name | Order Loinc | Result Code | Result Code Name | UofM | Result LOINC |
|---|---|---|---|---|---|---|
| 070038 | Testosterone, F Eqlib+T LC/MS | 58952-3 | 070036 | Testosterone, Total, LC/MS | ng/dL | 2986-8 |
| 070038 | Testosterone, F Eqlib+T LC/MS | 58952-3 | 070039 | Testosterone, Free | ng/dL | 2991-8 |
| 070038 | Testosterone, F Eqlib+T LC/MS | 58952-3 | 080770 | % Free Testosterone | % | 15432-8 |
| Order Code | 070038 | |||||
| Order Code Name | Testosterone, F Eqlib+T LC/MS | |||||
| Order Loinc | 58952-3 | |||||
| Result Code | 070036 | |||||
| Result Code Name | Testosterone, Total, LC/MS | |||||
| UofM | ng/dL | |||||
| Result LOINC | 2986-8 | |||||
| Order Code | 070038 | |||||
| Order Code Name | Testosterone, F Eqlib+T LC/MS | |||||
| Order Loinc | 58952-3 | |||||
| Result Code | 070039 | |||||
| Result Code Name | Testosterone, Free | |||||
| UofM | ng/dL | |||||
| Result LOINC | 2991-8 | |||||
| Order Code | 070038 | |||||
| Order Code Name | Testosterone, F Eqlib+T LC/MS | |||||
| Order Loinc | 58952-3 | |||||
| Result Code | 080770 | |||||
| Result Code Name | % Free Testosterone | |||||
| UofM | % | |||||
| Result LOINC | 15432-8 |