Free testosterone levels: published ranges and why labs differ

You have a free testosterone result, or you are thinking about getting one, and you want to know what range it should sit in. The honest answer is that there is no single range. It depends on the method the lab used and on the units on your report.

Free and total testosterone

Free and total testosterone on one order, so you get both numbers from one draw.

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What free testosterone is

Most testosterone in your blood is attached to proteins, mainly SHBG and albumin. MedlinePlus describes free testosterone as the unattached form, which is more available for your body to use. One large lab’s direct-assay page says free testosterone is typically less than 2% of total testosterone, and its dialysis page says less than 3%. The direct-assay page adds that in most men more than half of total testosterone is bound to SHBG.

So a free testosterone number is small, and it is reported in different units from total testosterone. For the full comparison, see free vs total testosterone and what is free testosterone.

A published range by age band: direct immunoassay

This age-banded table comes from one large lab’s published test page. It covers a direct analog enzyme immunoassay. The table is copied exactly. The source gives no range for ages 0 to 19 (“not established”), and its last row is labelled “over 59”.

The same page notes that gross lipemia (a very fatty sample) may give falsely high free testosterone results, and that the lab asks for the patient’s age and sex on the request form.

Published ranges for equilibrium dialysis

Equilibrium dialysis separates the free portion from the rest before it is measured. Two labs publish adult male ranges for it. Neither splits them by age band in the pages we read.

Method	Who	Range	Notes
Equilibrium dialysis, with mass spectrometry for total testosterone	Adult males	52 to 280 pg/mL	Also lists 1.5 to 3.2% free. Test page
Equilibrium dialysis with HPLC-tandem mass spectrometry	Males 18 years and older	47 to 244 pg/mL	The page says to collect between 6 and 10 a.m. Test page

Look at how far these sit from the direct immunoassay table above. The two methods do not report on the same scale. The direct-assay page itself says some researchers found its results to be about one-fourth as high as equilibrium dialysis. It also says others found the two comparable.

Why the method matters

The direct-assay test page describes a design in which a labelled testosterone analog competes for antibody binding sites. The Endocrine Society guideline’s full text recommends against direct analog immunoassays for free testosterone. So the age-band table above gives that lab’s range for that test, and applies to results from the same kind of test.

Look for these on your result:

• The method (equilibrium dialysis, direct or analog immunoassay, or calculated).
• The units (pg/mL here; some reports use ng/dL, and 1 ng/dL equals 10 pg/mL).
• The reference range printed next to your number.

A calculated value is a third route. The Endocrine Society guideline recommends obtaining a free testosterone concentration, either by equilibrium dialysis or by estimating it with an accurate formula, in men whose total testosterone is near the lower limit of normal or who have a condition that alters SHBG. If you want a free testosterone figure, the free and total test gives both numbers on one order. If you already have total and SHBG results, our free testosterone calculator estimates free testosterone from them. It is an estimate, not a lab result.

• Free and total testosteroneBoth numbers on one order $99 See this test at HealthLabs
• Free testosteroneFree testosterone only $59 See this test at HealthLabs
• Total testosteroneTotal testosterone only $49 See this test at HealthLabs

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When free testosterone is worth measuring

Most men who want to check their testosterone start with a total testosterone test. Free testosterone adds information in specific cases. The guideline abstract names two: a total result near the lower limit of normal, and a condition that changes SHBG. One lab’s page lists use “where the testosterone binding proteins may be altered,” with obesity, cirrhosis and thyroid disorders as examples.

If neither applies, a total test may be all you need. See the testosterone test guide or the test finder to pick.

What a free testosterone number cannot tell you

• It does not diagnose. MedlinePlus says a testosterone test alone cannot diagnose any condition. The Endocrine Society guideline recommends diagnosing low testosterone only in men with symptoms and signs of deficiency and unequivocally, consistently low results.
• It varies. Testosterone is typically highest in the morning, and one draw is one moment. See retesting.
• Ranges are not targets. A published range describes the lab’s reference group. It does not say what level you should have.

Take your result and its printed range to a clinician if you have symptoms such as low sex drive or erectile dysfunction, or if the result falls outside the range. Total testosterone ranges by age band are on the testosterone levels by age page.