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23077 Testosterone, Free (Includes Total and SHBG)

Testosterone, Free (Includes Total and SHBG)
Test Code: FT
Synonyms/Keywords
Free Testosterone, Testosterone Panel, Tot & Free​
Test Components
Testosterone, Sex Hormone Binding Globulin
Useful For

​Free testosterone testing is a second level test for suspected increases or decreases in physiologically active testosterone. 

To evaluate hirsutism and masculinization in women, testicular function in clinical states where the testosterone binding proteins may be altered (obesity, cirrhosis, thyroid disorders).

Assessment of functional circulating testosterone in early pubertal boys and older men.

Monitoring of testosterone therapy or anti-androgen therapy in older men and in females. 

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 60 minutes of venipuncture.  Specimen must be free of particulate matter including fibrin.  Specimens should be thawed and frozen up to two times.

For Marshfield Clinic and all other facilities, two tubes are required containing 1 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 Testosterone Total​ ​ ​ ​ Ambient 1 week
Refrigerated​ 2 weeks
Frozen 1 month
​For SHBG, consult Test Reference Manual ​ ​
Rejection Criteria

​Serum Separator Tube (SST)

Interference
​Heterophilic antibodies in human serum can react with the immunoglobulins included in the assay components causing interference with immunoassay.
Performing Laboratory Information
Performing Location Day(s) Test Performed Analytical Time Methodology/Instrumentation
Marshfield​ Monday through Friday 0700; test is batched and performed once/day​ 1 day Calculation by mathematical modeling
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.
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. 

Interpretation

​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.
Outreach CPTs
CPT Modifier
(if needed)
Quantity Description Comments

​84402

Synonyms/Keywords
Free Testosterone, Testosterone Panel, Tot & Free​
Test Components
Testosterone, Sex Hormone Binding Globulin
Ordering Applications
Ordering Application Description
​Centricity ​Testosterone, Free
​Cerner ​Testosterone Level Free
If the ordering application you are looking for is not listed, contact your local laboratory for assistance.
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

Separate serum from the blood within 60 minutes of venipuncture.  Specimen must be free of particulate matter including fibrin.  Specimens should be thawed and frozen up to two times.

For Marshfield Clinic and all other facilities, two tubes are required containing 1 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 Testosterone Total​ ​ ​ ​ Ambient 1 week
Refrigerated​ 2 weeks
Frozen 1 month
​For SHBG, consult Test Reference Manual ​ ​
Rejection Criteria

​Serum Separator Tube (SST)

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

​Free testosterone testing is a second level test for suspected increases or decreases in physiologically active testosterone. 

To evaluate hirsutism and masculinization in women, testicular function in clinical states where the testosterone binding proteins may be altered (obesity, cirrhosis, thyroid disorders).

Assessment of functional circulating testosterone in early pubertal boys and older men.

Monitoring of testosterone therapy or anti-androgen therapy in older men and in females. 

Test Components
Testosterone, Sex Hormone Binding Globulin
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. 

Interpretation

​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.
For more information visit:
Performing Laboratory Information
Performing Location Day(s) Test Performed Analytical Time Methodology/Instrumentation
Marshfield​ Monday through Friday 0700; test is batched and performed once/day​ 1 day Calculation by mathematical modeling
For billing questions, see Contacts
Outreach CPTs
CPT Modifier
(if needed)
Quantity Description Comments

​84402

For most current information refer to the Marshfield Laboratory online reference manual.