Search

Browse by Name

Accreditation Certificates

2026 CAP Certificate

Critical Value Information

Critical Values Policy

General Information

Clinical Requisition Form

Microbiology Requisition Form

Cytology Requisition Form

Pathology Requisition Form

Specimen Transport Pictoral

Marshfield Labs Website

Direct Access Links

Direct Access Information

Mayo Clinic Laboratories

Test Code FT Testosterone, Free (Includes Total and SHBG)

Useful For

Free testosterone testing is a second-level test used for suspected increases or decreases in physiologically active testosterone. Specifically, this test is used to evaluate hirsutism, masculinization in women, to rule out ovarian neoplasms and to evaluate testicular function in clinical states where the testosterone binding proteins may be altered (obesity, cirrhosis, thyroid disorders). This test is also useful in assessment of functional circulating testosterone in early pubertal boys and in older men, as well as for monitoring testosterone therapy or anti-androgen therapy in older men and females.

Synonyms/Keywords

Free Testosterone, Testosterone Panel, Tot & Free

Specimen Requirements

Fasting Required	Specimen Type	Preferred Container/Tube	Acceptable Container/Tube	Specimen Volume	Specimen Minimum Volume (allows for 1 repeat)	Pediatric Minimum Volume (no repeat)
No	Serum	Red Top Tube (RTT)		1.5 mL	1.0 mL	1.0 mL

Collection/Processing Instructions

Separate serum from the blood within 2 hours of venipuncture. Specimen must be free of particulate matter including fibrin. Specimens may be thawed and frozen up to two times.

For Marshfield Clinic and all other facilities, two tubes are required containing 0.5 mL for total testosterone and 0.5 mL for Sex Hormone Binding Globulin (SHBG).

Testosterone secretion is episodic. Serum testosterone levels in adult males peak in the early morning (7am), decreasing about 25% to the evening (minimum at about 8pm). Levels increase after exercise and decrease after immobilization and after glucose load.

Specimen Stability Information

Specimen Type	Temperature	Time
Serum	Refrigerated	7 days
Serum	Frozen	1 month

Rejection Criteria

Serum Separator Tube (SST)

Test Components

Testosterone, Sex Hormone Binding Globulin

Test Information

Most circulating testosterone is bound to sex hormone-binding globulin (SHBG), which in males also is called testosterone-binding globulin. A lesser fraction is albumin bound and a small proportion exists as free hormone. The concentration of free testosterone is very low, typically <2% of the total testosterone concentration. It was initially understood that only the free testosterone was thought to be the biologically active component. However, testosterone weakly bound to serum albumin which dissociates freely in the capillary bed, becomes readily available for tissue uptake. Therefore, all non-SHBG-bound testosterone is considered bioavailable.

Interferences

Heterophilic antibodies in human serum can react with the immunoglobulins included in the assay components causing interference with immunoassay.

Interpretations

Testosterone results should be interpreted in light of the total clinical presentation of the patient, including: symptoms, clinical history, data from additional tests and other appropriate information.

Measurement of total testosterone is often sufficient for diagnosis, particularly if it is combined with measurements of LH (Luteinizing Hormone) and FSH (Follicle Stimulating Hormone). However, these tests may be insufficient for diagnosis of mild abnormalities of testosterone homeostasis, particularly if the abnormalities in SHGB (Sex Hormone Binding Globulin) function or levels are present. Additional measurements of bioavailable testosterone or/and free testosterone are recommended in this situation.

Usually, bioavailable and free testosterone levels parallel the total testosterone levels. However, a number of conditions and medications are known to increase or decrease the sex hormone-binding globulin (SHBG) concentration, which may cause total testosterone concentration to change without necessarily influencing the bioavailable of free testosterone concentration, or vice versa:

Treatment with corticosteroids and sex steroids (particularly oral conjugated estrogen) can result in changes in SHBG levels and availability of sex-steroid binding sites on SHBG. This may make diagnosis of subtle testosterone abnormalities difficult.
Inherited abnormalities in SHBG binding
Liver disease and severe systemic illness
In pubertal boys and adult men, mild decreases of total testosterone without LH abnormalities can be associated with delayed puberty or mild hypogonadism. In this case, either bioavailable or free testosterone measurements are better indicators of mild hypogonadism than determination of total testosterone levels.
In polycystic ovarian syndrome and related conditions, there is often significant insulin resistance, which is associated with low SHBG levels. Consequently, bioavailable or free testosterone levels may be more significantly elevated. While free testosterone can be used for the same indications as bioavailable testosterone, determination of testosterone levels may be superior to free testosterone measurement in most situations.

Reference Range Information

Performing Location	Reference Range
Marshfield	Males All ages: 4.4 - 16.5 ng/dL Females All ages: <0.2 - 1.0 ng/dL Reference intervals are not established for population <18 yrs. Free Testosterone is estimated by calculations based on Vermuelen method which involves a calculation based on mass action equations measuring total testosterone, sex hormone binding globulin and constant albumin value and from the association constants for binding of testosterone to the two binding proteins (J Endocrinol Metab 1999; 84:3666). Free testosterone estimated by mathematical modeling show good correlation with equilibrium dialysis measurements and are considered a reliable indicator of free testosterone. Conditions resulting in abnormal plasma protein concentrations such as nephrotic syndrome, cirrhosis and pregnancy require adjustment in the assumption for albumin concentration. Serum and plasma values for testosterone should not be used interchangeably. Values obtained by different Immunoassays may differ and cannot be used interchangeably. Results obtained by LC/Tandem mass spectrometry cannot be compared with calculated results.

Performing Location

Reference Range

Marshfield

Males All ages: 4.4 - 16.5 ng/dL

Females All ages: <0.2 - 1.0 ng/dL

Reference intervals are not established for population <18 yrs.

Free Testosterone is estimated by calculations based on Vermuelen method which involves a calculation based on mass action equations measuring total testosterone, sex hormone binding globulin and constant albumin value and from the association constants for binding of testosterone to the two binding proteins (J Endocrinol Metab 1999; 84:3666). Free testosterone estimated by mathematical modeling show good correlation with equilibrium dialysis measurements and are considered a reliable indicator of free testosterone.

Conditions resulting in abnormal plasma protein concentrations such as nephrotic syndrome, cirrhosis and pregnancy require adjustment in the assumption for albumin concentration.

Serum and plasma values for testosterone should not be used interchangeably. Values obtained by different Immunoassays may differ and cannot be used interchangeably. Results obtained by LC/Tandem mass spectrometry cannot be compared with calculated results.

Marshfield Labs Performing Department

Marshfield Labs Special Chemistry

Performing Information

Performing Location	Day(s) Test Performed	Analytical Time	Methodology/Instrumentation
Marshfield (Special Chemistry; Immunodiagnostics)	Monday through Friday 0700; test is batched and performed once/day	1 day	Calculation by mathematical modeling

Performing Location

Day(s) Test Performed

Analytical Time

Methodology/Instrumentation