Testosterone, Free (Equilibrium Ultrafiltration) with Total Testosterone » Pathology Laboratories » College of Medicine

Additional Information:

UFHPL Epic order code: LAB5752

The concentration of free testosterone is very low, typically 50% of total circulating testosterone is bound to sex hormone-binding globulin (SHBG) and most of the rest is bound to albumin.² Routinely available assay methods used to measure total testosterone are not sensitive enough to accurately quantitate 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.^3,4 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 by filtration through a membrane by centrifugal ultrafiltration.⁵ 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.

Footnotes

Tietz NW, ed. Clinical Guide to Laboratory Tests. 3rd ed. Philadelphia, Pa: WB Saunders Co; 1995:578.
Wheeler MJ. The determination of bioavailable testosterone. Ann Clin Biochem. 1995; 32(Pt 4):345-357 (review). PubMed 7486793
Klee GG, Heser DW. Techniques to measure testosterone in the elderly. Mayo Clin Proc. 2000; 75(Suppl):S19-S25. PubMed 10959211
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.
Vlahos I, MacMahon W, Sgoutas D. An improved ultrafiltration method for determining free testosterone in serum. Clin Chem. 1982; 28(11):2286-2291.PubMed 7127776

CPT Code(s):

84402, 84403

Specimen Requirements:

Important: Indicate the patient’s age and gender when ordering this test.

Type: Serum

Container/Tube: Red-top tube or gel-barrier tube

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

Sample Volume: 0.8 mL

Minimum Volume: 0.3 mL (Repeat testing is not possible with this specimen volume.)

Storage: Refrigerate specimens after collection.

Stability (collection to time of analysis/testing):

Ambient: 14 days
Refrigerated: 14 days
Frozen: 14 days
Freeze/Thaw cycles: Stable (x3)

Rejection Criteria:

Gross lipemia
Recently administered isotopes
Plasma specimen

Use:

This test is used to evaluate hirsutism and masculinization in women; evaluate testicular function in clinical states where the testosterone binding proteins may be altered (obesity, cirrhosis, thyroid disorders)

This test includes total, free, and percent free testosterone.

Methodology:

Free: equilibrium ultrafiltration; total: electrochemiluminescence immunoassay (ECLIA)

Reported:

2 – 4 days

Reference Values:

Age	Male (ng/dL)	Female (ng/dL)
Free Testosterone
Cord blood	0.50 − 2.20	0.40 − 1.60
1−15 days old	0.15 − 3.10	0.05 − 0.25
1 − 2 months old	0.33 − 0.80	0.01 − 0.13
3 − 5 months old	0.07 − 1.40	0.03 − 0.11
6 − 7 months old	0.04 − 0.48	0.02 − 0.06
6 − 9 years old	0.01 − 0.32	0.01 − 0.09
10 − 11 years old	0.06 − 0.57	0.10 − 0.52
12 − 14 years old	0.14 − 15.60	0.10 − 0.52
15 − 17 years old	8.00 − 15.90	0.10 − 0.52
Adults	5.00 − 21.00	0.10 − 0.85
Percentage of Total Testosterone
Cord blood	2.00 − 4.40	2.00 − 3.90
1 − 15 days old	0.90 − 1.70	0.80 − 1.50
1 − 2 months old	0.40 − 0.80	0.40 − 1.10
3 − 5 months old	0.40 − 1.10	0.50 − 1.00
6 − 7 months old	0.40 − 1.00	0.50 − 0.80
6 − 9 years old	0.90 − 1.70	0.90 − 1.40
10 − 11 years old	1.00 − 1.90	1.00 − 1.90
12 − 14 years old	1.30 − 3.00	1.00 − 1.90
15 −17 years old	1.80 − 2.70	1.00 − 1.90
Adults	1.50 − 4.20	0.50 − 2.80