Free Testosterone: The Active Hormone Your Cells Use

Free testosterone refers to the portion of testosterone in the bloodstream that is not bound to proteins, such as sex hormone-binding globulin (SHBG) or albumin. This form of testosterone is considered the active form because it can easily enter cells and exert its biological effects. Free testosterone is a crucial factor in various bodily functions, including libido, muscle mass maintenance, bone density, and mood regulation. While total testosterone levels are essential, free testosterone levels provide a more accurate representation of the hormone's availability for cellular uptake, utilization and better correlates with signs and symptoms.

NiaHealth’s lab uses a calculated formula to derive free testosterone. While concerns about the accuracy of estimated free testosterone (eFT) are understandable, current clinical practice does not support direct measurement as the preferred approach. The gold standard for measuring free testosterone is equilibrium dialysis, but this test is not easily accessed in Canada and is rarely used due to cost and logistical constraints. Instead, Vermeulen’s algorithm is a widely accepted method for estimating free testosterone from total T, SHBG, and albumin levels​.

Testosterone plays a key role in the development and maintenance of male secondary sexual characteristics, including muscle mass, body hair, and a deep voice. It also influences libido and sexual function in both men and women. Additionally, testosterone supports bone health, contributing to bone density and strength.

Testosterone is essential for energy, mood, and cognitive function. It has a significant impact on muscle and overall body composition. Low testosterone levels can lead to symptoms like fatigue, reduced muscle mass, mood changes, and sexual dysfunction, while excessively high levels can result in adverse health effects, such as cardiovascular issues.

Low testosterone levels in men, known as hypogonadism, can lead to a range of symptoms and may require treatment.

As of March 13, 2025, NiaHealth has removed separate optimal and normal ranges for free testosterone based on additional research our clinical experience. Instead greater emphasis will be placed on total testosterone levels. The reason for this change are as follows.

- Binding Proteins & Bioavailability: Unlike total testosterone, which measures all circulating testosterone (both bound and unbound), free testosterone accounts for only the fraction that is not tightly bound to SHBG and is available for biological activity. Since SHBG levels fluctuate due to age, metabolic health, and hormonal balance, free testosterone levels can vary significantly even when total testosterone remains within a normal range.

- Assay Variability: Measuring free testosterone accurately is more complex than total testosterone. Direct assays often lack precision, and calculated free testosterone depends on assumptions about SHBG and albumin binding, leading to inconsistencies between different measurement methods.

- Lack of Standardized Reference Ranges: While total testosterone reference ranges are well-established based on large population studies, free testosterone ranges are less standardized due to differences in measurement techniques and population variability. This makes it harder to determine a universal "optimal" range.

Because of these complexities, clinicians often interpret free testosterone in conjunction with total testosterone and SHBG levels rather than relying on a single threshold for optimization.