Testosterone, Free (Direct)

The unbound, biologically active fraction of testosterone.

Last reviewedJune 16, 2026

Serum

sample type

~5 mL

blood needed

~7 days

results in app

Morning, 7 to 10am

best timing

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Why test Reference ranges What you'll learn What affects it How testing works Sources FAQ

In short

Free testosterone is the small fraction of testosterone that circulates unbound to any protein, so it is fully available to your tissues. This test measures it directly rather than calculating it.

Only a few percent of total testosterone is free, so the direct measurement is sensitive to method. It is taken from a morning serum sample because testosterone is highest early in the day.

Sex Hormones & Fertility

Reviewed against DGKL reference practice.

Why test this?

Free testosterone reflects the active hormone better than total testosterone when binding proteins are unusual. It helps explain symptoms of low or high androgen activity that the total level alone does not.

Low free testosterone can contribute to low energy, low libido, and reduced muscle and bone strength. High levels in women can point to androgen excess such as PCOS.

What is a normal result?

Aniva reads your result against research-backed ranges, not just the lab's wide normal. The reference shown below is specific to this biomarker.

Typical adult male guidance, assay dependent:

Result	Range
Free testosterone (men)	0.2 to 0.62 nmol/L

Roughly 5.5 to 18 ng/L. Values are much lower in women and depend heavily on the method. Read against your lab's reference interval.

Ranges are guidance and vary by lab and assay, aligned with DGKL practice. Always read your result against your own lab's reference interval.

What insights will this test give you?

The amount of testosterone directly available to your tissues.
A clearer read on androgen activity when SHBG is high or low.
A result best interpreted with total testosterone and SHBG.

What can affect this result?

What can skew the result

Free testosterone varies through the day and peaks in the morning. Direct immunoassays can be less accurate than equilibrium methods. Illness, obesity, and medicines that change SHBG affect interpretation. Biotin can interfere with some assays.

Best interpreted with

Read alongside total testosterone, SHBG, and the free testosterone index.

How is this tested?

Sample

Serum

Blood needed

~5 mL

Method

Immunoassay

Best timing

Morning, 7 to 10am

Sources. The evidence behind this

LOINC 2991-8: Testosterone Free [Mass/volume] in Serum or Plasma

Mayo Clinic Laboratories: Testosterone, Free, Serum

Endocrine Society: Clinical Practice Guidelines

Common questions

Which Aniva panels include this marker?

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