S-testosterone, bioactive

Free testosterone

Free testosterone is a form of testosterone that circulates in the blood and is not bound to any proteins, making it available for the body's tissues to use.

What is free testosterone?

Testosterone is a male sex hormone that is also present in women in smaller amounts.

The total testosterone in the blood includes both bound and free testosterone. Most of the testosterone in the blood is bound to proteins called globulins, mainly sex hormone-binding globulin (SHBG). Only a small amount of testosterone is freely and immediately available for the body's cells to use.

Why analyze free testosterone?

Free testosterone may be important to calculate in certain medical conditions, such as erectile dysfunction or male infertility. It can also be calculated as part of hormonal evaluations in case of suspected hormonal imbalance in both men and women.

Calculate free testosterone

Free testosterone can be measured in different ways, but a common way is to use a mathematical model that takes into account the total testosterone value and the level of SHBGin the blood. This model is called "estimated free testosterone".

Model takes into account the total testosterone value and the amount of SHBG protein to which the testosterone is bound. The higher the level of SHBG in the blood, the less free testosterone is available. This may be relevant in hormonal evaluations, where both total testosterone and SHBG levels are measured together with calculated free testosterone to provide a more complete picture of hormone balance.

Formula for free testosterone

The formula for calculating bioactive testosterone also takes into account the biomarker albumin, another protein that can bind to testosterone but to a lesser extent than SHBG. The formula may vary slightly depending on which laboratory is used, but a commonly used formula is:
Free Testosterone = Total Testosterone x (0.67 x Albumin/(SHBG x 100))
In this formula, albumin and SHBG are used to adjust binding proteins and obtain an estimate of the free proportion of testosterone in the blood.

Reference range - free testosterone


  • 0.15 - 1.4 nmol/L


  • 17 - 40 years: 2.8 - 21 nmol/L
  • 41 - 60 years: 2.0 - 15 nmol/L
  • > 60 years: 1.4 - 14 nmol/L

High levels of free testosterone

High levels of free testosterone can also cause symptoms such as acne, increased body hair, mood changes and reduced sleep quality.

Low levels of free testosterone

Low levels of free testosterone can also cause symptoms such as decreased sex drive, fatigue, muscle weakness, depression and decreased bone mass.

Low levels of free testosterone can affect fertility, but this is not always the case. Testosterone is an important hormone for sexual function and reproduction, and a lack of testosterone can lead to reduced sperm production and reduced fertility in men.

Tests containing the marker Free testosterone

Hormone tests

Hormone tests

Free testosterone
Testosterone test incl. SHBG

Free testosterone

  • Calculates your level of free testosterone in the blood.
  • Also analyzes SHBG and total testosterone.
  • Provides increased insight into your testosterone levels.

395 kr

Bioactive testosterone (free)

Testosterone bioactive

  • Measures your level of free testosterone, unbound
  • Health test to identify testosterone deficiency
  • Get insight into the availability of free testosterone

189 kr

Health checks

Health checks

Health check man plus
Comprehensive health check

Health check man plus

  • Comprehensive health check for men.
  • Includes 65 different health tests.
  • Provides insight into your health data.
  • 10 different health areas.

4 595 kr3 895 kr

Testosterone Plus
Health check Testosterone plus

Testosterone Plus

  • Health check that gives an insight into your testosterone production
  • Analysis of markers that affect reduced muscle mass, feelings of pleasure and fatigue.
  • Gives you better conditions to optimize your health.

1 095 kr