Testosterone, Free, Equilibrium Ultrafiltration With Total Testosterone, LC/MS-MS

CPT: 84402; 84403
Updated on 12/2/2018
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Test Details

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)

Methodology

Free: equilibrium ultrafiltration; total: liquid chromatography/tandem mass spectrometry (LC/MS-MS)

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 Requirements

Specimen

Serum

Volume

2.5 mL

Minimum Volume

1 mL (Note: This volume does not allow for repeat testing.)

Container

Red-top tube or gel-barrier tube

Collection

Serum should be transferred from cells within one hour of collection and transferred to a plastic transport tube.

If a red-top tube is used, transfer separated serum to a plastic transport tube.

Serum should be transferred from cells within one hour of collection and transferred to a plastic transport tube.

Storage Instructions

Refrigerate

Stability Requirements

Temperature

Period

Room temperature

7 days

Refrigerated

7 days

Frozen

5.58 years

Freeze/thaw cycles

Stable x9

Temperature

Period

Room temperature

7 days

Refrigerated

7 days

Frozen

5.58 years

Freeze/thaw cycles

Stable x9

Causes for Rejection

Gross lipemia; recently administered isotopes; plasma specimen; improper labeling; specimen drawn in citrate or ACD tube

Gross lipemia; recently administered isotopes; plasma specimen

Gross lipemia; recently administered isotopes; plasma specimen; improper labeling; specimen drawn in citrate or ACD tube

Clinical Information

Special Instructions

State patient's age and sex on the test request form.

Footnotes

1. Wheeler MJ. The determination of bioavailable testosterone. Ann Clin Biochem. 1995; 32(Pt 4):345-357 (review). 7486793
2. Klee GG, Heser DW. Techniques to measure testosterone in the elderly. Mayo Clin Proc. 2000; 75(Suppl):S19-S25. 10959211
3. Gronowski AM, Landau-Levine M. Reproductive endocrine function. In: Burtis CA, Ashwood ER, eds. Tietz Textbook of Clinical Chemistry. 3rd ed. Philadelphia, Pa: WB Saunders Co; 1999:1601-1641.
4. Vlahos I, MacMahon W, Sgoutas D. An improved ultrafiltration method for determining free testosterone in serum. Clin Chem. 1982; 28(11):2286-2291. 7127776

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
070038 Testosterone, F Eqlib+T LC/MS 070036 Testosterone, Total, LC/MS ng/dL 2986-8
070038 Testosterone, F Eqlib+T LC/MS 070039 Testosterone, Free ng/dL 2991-8
070038 Testosterone, F Eqlib+T LC/MS 080770 % Free Testosterone % 15432-8

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The LOINC® codes are copyright © 1994-2018, Regenstrief Institute, Inc. and the Logical Observation Identifiers Names and Codes (LOINC) Committee. Permission is granted in perpetuity, without payment of license fees or royalties, to use, copy, or distribute the LOINC® codes for any commercial or non-commercial purpose, subject to the terms under the license agreement found at https://loinc.org/license/. Additional information regarding LOINC® codes can be found at LOINC.org, including the LOINC Manual, which can be downloaded at LOINC.org/downloads/files/LOINCManual.pdf