Getting tested properly

A large share of 'low testosterone' diagnoses fall apart on a correct retest. The rules for getting an honest number are simple, and skipping them is how men end up on lifelong therapy they never needed — or missing a real problem.

The rules

How to draw it: Testosterone peaks in the morning and dips through the day, so it must be drawn before ~10–11am, ideally fasting. Diagnosis requires two low total-T readings on separate mornings plus symptoms — not one value, and not an afternoon draw. Roughly 30% of initially low readings are normal on repeat, because acute illness, poor sleep, or timing suppress a single measurement. Evidence ●●●●●
The thresholds: Guideline cutoffs sit around a total testosterone of 264 ng/dL (Endocrine Society harmonised lower limit) to 300 ng/dL (AUA) — but a number just under a line, with no symptoms, is not a diagnosis. When total T is borderline or SHBG is skewed, add free testosterone before deciding anything.

The rest of the panel

What else to check: A proper work-up adds LH and FSH (to locate the problem — see the next section), and, when those are low or normal despite low T, prolactin and iron studies (haemochromatosis is a treatable cause). If treatment is on the table, baseline safety markers matter too: haematocrit and, in men over ~40, PSA.

One morning draw is not a diagnosis

If a single, possibly mistimed test is the only basis for a testosterone prescription, ask for a repeat morning fasting measurement and LH/FSH first. The retest alone reclassifies a large minority of men as normal.

The Testosterone Guide