The procedure for calculating free testosterone

To calculate free testosterone is used:

  1. An indicator of the level of albumin concentration (in the absence of laboratory data, a constant albumin concentration of 4.3 g / dl is used).
  2. An indicator of the level of total testosterone.
  3. An indicator of the level of globulin that binds sex steroids (SHGS, SSSG - SHBG).

Enter the available indicators of albumin, testosterone level and SHBG in the appropriate fields, choosing the appropriate units. After filling in all the fields, click on the “Calculate” button, after which the values ​​of free and bioavailable testosterone will be obtained in the “Results” field.

The results of the calculator should not be used by the patient on their own without first consulting a specialist.

A warning! Estimated free and bioavailable testosterone data are reliable in most clinical situations, but you should not use a calculator for physiological and pharmacological increase in androgens (for example, in girls during menstruation, and in men during treatment with testosterone ).

The calculator was developed at the Department of Hormonology, University Hospital of Ghent, Belgium.

Forms (fractions) of testosterone

Three forms of testosterone are distinguished:

  • ; Associated with SHSS - inactive form (about 57%) ;
  • ; Associated with albumin - active (bioavailable) form (about 40%) ;
  • . Free testosterone - has a maximum bioavailability (1-3%) .
Total Testosterone =   T linked to SHGP + T bound to albumin + T free.

Thus, the level of total testosterone indicates a quantitative indicator of all forms of T in the blood, and in some cases cannot be used as a determining indicator of the degree of androgen deficiency, because the level of total testosterone may remain normal, while the T inactive form will prevail over its bioavailable fraction.

Bioavailable testosterone = T bound to albumin + T free.

It is bioavailable forms of T that affect the body, because able to penetrate into androgen-sensitive cells, which can not T associated with GPSS, because of their strong connection.

Methods for determining the level of free testosterone

Table 1 - Methods for determining the level of free testosterone (Dedov I.I., Kalinchenko S.Yu., 2006)

Double (equilibrium) dialysis + +++ +
Radioimmunological analysis (RIA) ++ + ++
Ultracentrifugation + +++ +
Determination of Estimated Free Testosterone +++ +++ +++
Determination of the concentration of free testosterone in saliva ++ +++ ++

Since modern methods for determining free testosterone are laborious and inaccessible (Table 1), the determination of calculated free testosterone is the method of choice because of its availability and reliability.

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