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Testosterone, Free and Bioavailable, Male

Includes SHBG

Test Codes

EPIC: LAB7038, SOFT: TESTM

Department

Toxicology

Instructions

This test should be ordered on males 18 and older and includes:

• Measured total with calculated free and bioavailable testosterone.
• Sex hormone binding globulin (SHBG).

Specimen Collection Criteria

Collect (preferred specimen): One Gold-top SST tubes. (Minimum Whole Blood: 4.0 mL)
Also acceptable: One plain Red-top tube.

• Contact the Laboratory for acceptability of other tube types.
• Due to diurnal variation, it is recommended that the specimen be collected between 6:00 am – 10:00 am, however, it is not required and specimens collected at other times will not be rejected.

Physician Office/Draw Specimen Preparation

Let specimens clot 30-60 minutes then centrifuge within 2 hours of collection to separate serum from cells. Transfer serum to a plastic transport tube and refrigerate (2-8°C or 36-46°F).

Preparation for Courier Transport

Transport: 2.0 mL serum, refrigerated (2-8 °C or 36-46 °F). (Minimum Serum: 1.0 mL)

Rejection Criteria

Specimens collected with EDTA.

Specimens not collected and processed as indicated.

In-Lab Processing

Let specimens clot 30-60 minutes then centrifuge within 2 hours of collection to separate serum from cells. Transfer serum to a plastic transport tube and refrigerate (2-8°C or 36-46°F).

Storage

Specimen Stability for Testing:

Room Temperature (20-26°C or 68-78.8°F): 48 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): 2 months

Specimen Storage in Department Prior to Disposal:

Specimen retention time is determined by the policy of the reference laboratory. Contact the Send Outs Laboratory with any questions.

Laboratory

Royal Oak Toxicology Laboratory

Performed

Sunday – Saturday.
Results available in 2-6 days.

Reference Range

By report.....

Test Methodology

Quantitative Electrochemiluminescent Immunoassay.

Clinical Utility

• Testosterone is present in both protein bound (presumably inactive) and unbound (theoretically active) forms.  Accurate measurements of testosterone and its bound and unbound sub-fractions are important in the assessment of hypogonadism in men.  Testosterone measurement using LC-MS/MS is designed to measure low total testosterone concentrations observed in some males with hypogonadism, due to decreased precision and specificity of available immunoassays at low hormone concentrations.
• Free testosterone concentrations are frequently about 2% of the total concentration, but may vary due to changes in concentrations of hormone binding proteins, the concentration of endogenous competitors for binding sites, renal status and hepatic disease. Sex hormone binding globulin (SHBG) is a low capacity, high affinity protein that accounts for about 40-50% of the bound testosterone in men and 60-80% in women (3). Albumin is a high capacity, low affinity protein that binds the remainder of the testosterone with the exception of a small fraction that remains unbound or free. When SHBG concentrations are high, more of the testosterone is in the bound state and less testosterone is available for biological activity and the % free testosterone is decreased. When SHBG concentrations are low, more testosterone is in the free state and the % free is elevated. Changes in binding protein concentrations in theoretical models typically do not change the concentration of free testosterone but may cause a fluctuation in total concentrations in that metabolism of testosterone is considered to be controlled by the % of the total that is free. In such a circumstance, the use of total testosterone measurements as an assessment of hormonal status may be misleading and a more appropriate measure may be the free testosterone concentration. Reporting the total testosterone, the concentrations of binding proteins, and an estimate of the free testosterone concentration is likely to permit a rational evaluation of a patient's hormonal status.
• Testosterone that is not bound to sex hormone binding globulin is referred to as bioavailable testosterone. It consists of the sum of the albumin-bound and unbound testosterone concentrations. This typically represents about 50-60 % of the total circulating testosterone in men and 20-30% in women. Bioavailable testosterone is not easily measured, and the reported result in this test combination is based on a calculation derived from the measurement of total testosterone by LC-MS/MS, SHBG, and albumin concentrations in serum (4).

Reference

1. Rosner W, Auchus RJ, Azziz, R, Sluss PM, Raff H. Position Statement: Utility, Limitations, and Pitfalls in Measuring Testosterone: An Endocrine Society Position Statement. JCEM 92:405-413, 2007.
2. Taieb J, Mathian B. Millot F, Patricot M-C, Mathieu E, Queyrel N, Lacroix I, Somma Delpero C, Boudou P. Testosterone Measured by 10 Immunoassays and by Isotope-Dilution Gas Chromatography Mass-Spectrometry in Sera from 116 Men, Women, and Children. Clin Chem 49:1381-1395, 2003.
3. LePage R. Review: Measurement of Testosterone and its Sub-fractions in Canada. Clin Biochem 39:97-108, 2006.
4. Emadi-Konjin P, Bain J, Bromberg IL. Evaluation of an Algorithm for Calculation of Serum “Bioavailable" Testosterone (BAT). Clin Biochem 36:591-596, 2003.

CPT Codes

84402, 84270, 84403 
LOINC: 2986-8, 2991-8, 2990-0, 13967-5, 15432-8

Contacts

Last Updated

1/26/2023