Testosterone, Free

Test Code
18944


CPT Codes
84402

Preferred Specimen
2.8 mL serum collected in a red-top tube (no gel)


Minimum Volume
1.3 mL


Instructions
Specify age and sex on test request form


Transport Container
Plastic screw-cap vial


Transport Temperature
Room temperature


Specimen Stability
Room temperature: 7 days
Refrigerated: 7 days
Frozen: 2 years


Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Gross hemolysis • Grossly lipemic • Serum Separator Tube (SST®)


Methodology
Chromatography/Mass Spectrometry • Calculation (CALC) • Immunochemiluminescence Assay (ICMA)

FDA Status
This test was developed and its analytical performance characteristics have been determined by Quest Diagnostics. It has not been cleared or approved by the U.S. Food and Drug Administration. This assay has been validated pursuant to the CLIA regulations and is used for clinical purposes.

Setup Schedule
Set up: Mon-Fri; Report available: 2 days


Reference Range
  Male (pg/mL) Female (pg/mL)
<1 Year Not established Not established
1-11 Years ≤1.3 ≤1.5
12-13 Years ≤64.0 ≤1.5
14-17 Years 4.0-100.0 ≤3.6
18-69 Years 46.0-224.0 0.2-5.0
70-89 Years 6.0-73.0 0.3-5.0
>89 Years Not established Not established


Clinical Significance

This test may aid in the diagnosis of hypogonadism in men, especially when total testosterone level is near the lower limit of the normal range or when sex hormone-binding globulin (SHBG) concentrations are affected by certain conditions. This test may also aid in the diagnosis of hyperandrogenemia in women [1-3].

Testosterone circulates in 3 major forms: unbound (free), weakly bound to albumin, and tightly bound to SHBG. Free testosterone comprises 2% to 4% of total testosterone and is biologically active. In this panel, free testosterone concentration is calculated based on measurements of total testosterone, SHBG, and albumin.

In men, fasting total testosterone concentrations measured in the morning are recommended for screening for hypogonadism [2]. Free testosterone level generally correlates well with total testosterone level except in individuals with conditions affecting SHBG concentrations, such as obesity, diabetes mellitus, nephrotic syndrome, aging, acromegaly, HIV disease, liver diseases, thyroid diseases, use of steroids and anticonvulsants, and polymorphisms in the SHBG gene. In these individuals and individuals whose total testosterone levels are at the lower limit, free testosterone levels are more sensitive than total testosterone levels for assessing androgen status. When the total testosterone level is low or total testosterone is normal but free testosterone is low, the fasting total testosterone level should be confirmed on another morning [2].

In women with normal total testosterone levels but strong clinical suspicion of hyperandrogenemia or moderate to severe
sexual hair growth, morning total and free testosterone may be measured [3]. Free testosterone levels correlate well with clinical presentations of hyperandrogenism and may serve as a more sensitive marker than total testosterone levels for diagnosing and monitoring the progress of hyperandrogenism [1].

This test uses a calculation based on measurements of total testosterone, SHBG, and albumin to derive the free testosterone level. Equilibrium dialysis is considered more accurate for measuring free T [1].

The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.

References
1. Rosner W, et al. J Clin Endocrinol Metab. 2007;92(2):405-413.
2. Bhasin S, et al. J Clin Endocrinol Metab. 2018;103(5):1715-1744.
3. Martin KA, et al. J Clin Endocrinol Metab. 2018;103(4):1233-1257.



Performing Laboratory
Quest Diagnostics Nichols Institute
14225 Newbrook Drive
Chantilly, VA 20153



The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.