Total Testosterone
The Screening Number - Assay Methods, the 264/300 ng/dL Cutoffs, and Two-Sample Confirmation
Evidence grade 5 of 5, Settled. Read how the Atlas grades evidence.
The written rationale for this grade is still being prepared.
- FDA
- A laboratory measurement, not an FDA product; run in CLIA labs. LC-MS/MS is the reference method; CDC HoSt certifies accuracy.
Reference only. Not medical advice.
What can go wrong
Acting on a single, mistimed, or immunoassay-derived total-T value both misses true hypogonadism and manufactures false positives that funnel healthy men onto lifelong therapy. Total T also misleads whenever SHBG is abnormal: a high-SHBG man may look normal on total T while his bioavailable fraction is low, and a low-SHBG (obese, diabetic) man may look low on total T while his free testosterone is adequate.
This is something to take to a clinician. The Atlas can tell you what is known about total testosterone in general. It cannot tell you what is happening in your body, and the difference matters most for exactly the symptoms that bring people to this page.
Total testosterone is the sum of all testosterone in serum: the ~44-65% bound tightly to SHBG, the ~30-40% bound loosely to albumin, and the 1-3% that is free. It is the first-line screening measurement for hypogonadism. The Endocrine Society (2018) uses a harmonized lower limit of 264 ng/dL (from Travison 2017, CDC-standardized); the AUA (2018) uses a rounder 300 ng/dL cutoff. Both guidelines require an early-morning draw and confirmation on a second separate morning sample before any diagnosis is made - a discipline the direct-to-consumer market routinely skips.
The single number the whole TRT funnel is built on - and the one most abused by timing and method.
What people take it for
What it is taken for. Approval, where it exists, covers only some of these.
How it works
Testosterone circulates almost entirely protein-bound. Total testosterone captures every fraction regardless of bioavailability, which is why it can mislead when the binding proteins are abnormal (high or low SHBG). Levels follow a diurnal rhythm, peaking in the morning and falling through the day - by afternoon a man can drop below a cutoff he cleared at 8 AM. Food, acute illness, and even a bad night's sleep transiently lower the number.
The catch: one number, three ways to be wrong
A total-T value can be wrong for method (a non-standardized immunoassay biased near the low threshold), timing (an afternoon or non-fasting draw), or biology (regression to the mean - a low value on a single day often rises on repeat). The guideline machinery - morning draw, fasting, two samples, CDC-certified assay - exists precisely because a single random number is unreliable. A checkout that sells therapy off one at-home finger-prick has removed every one of those safeguards.
What people get wrong
Often saidMy testosterone is 'low' because one test said so
ActuallyA single value near the threshold frequently regresses upward on repeat. Both major guidelines require two separate morning measurements before the label applies.
Often saidAny lab draw at any time of day is fine
ActuallyTestosterone peaks in the morning and can fall 20-25% by afternoon. An afternoon draw can push a normal man below a cutoff he would clear at 8 AM.
Often said264 and 300 are the same rule with rounding
ActuallyThey come from different bodies and datasets. 264 ng/dL is the CDC-harmonized 2.5th percentile of young healthy men (Travison); 300 ng/dL is the AUA's pragmatic clinical cutoff. Neither is a target to 'optimize' toward.
Who profits, and who pushes back
Shalender Bhasin, MD
The diagnosis requires symptoms plus unequivocally and consistently low morning testosterone - not a single convenient number.
What we do not know
- How many DTC 'low T' diagnoses would fail to confirm on a proper second morning, fasting, CDC-certified draw?
- Should regulators require at-home panels to disclose assay method and draw-timing caveats at point of sale?
At a glance
- Reference method
- Isotope-dilution LC-MS/MS (CDC HoSt-certified)
- Endocrine Society lower limit
- 264 ng/dL (harmonized, Travison 2017)
- AUA cutoff
- <300 ng/dL on two morning draws
- Draw requirement
- Early morning (before ~10 AM), fasting preferred
- Confirmation
- Two separate morning samples
What this entry does not yet cover
What follows is unfinished work on our side, not a finding about Total Testosterone. A short entry is not a safe entry.
- Timeline. We have not built the dated record of research and regulatory events.
- Cost and market. We have not documented what it sells for or who sells it.
- Supply chain. We have not mapped where it is made.
- Who uses it. We have not documented the user groups.
- What could change. No forward-looking summary yet.
- How it compares. We have not set it against the alternatives.
- Children and teenagers. We have not checked what is known about younger people.
Sources
The studies below are named and described, but not linked. You cannot open them from here and check our reading against them, which means this page is our summary of the literature rather than a document you can verify. Weigh it accordingly until the links exist.
The studies that matter
Travison et al., harmonized reference ranges, JCEM2017
Pooled 9,054 men across Framingham, EMAS, MrOS, and a Swedish sibling cohort; healthy nonobese men 19-39 had 2.5th-97.5th percentile of 264-916 ng/dL (median 531)
Bhasin et al., Endocrine Society Clinical Practice Guideline2018
Recommends diagnosing hypogonadism only with consistent symptoms plus unequivocally low morning total T measured by an accurate, ideally CDC-certified assay, confirmed on a repeat sample
Mulhall et al., AUA Testosterone Deficiency Guideline2018
Defines low testosterone as <300 ng/dL on at least two early-morning measurements, preferably same lab and method