The panel / Androgens
Total testosterone
Total testosterone is the number almost everyone means when they say they got their testosterone checked. It is also the number most often misread, because it measures the whole circulating supply rather than the part your body can use, and because it moves enough hour to hour that a single reading is not a diagnosis.
What it measures
Testosterone travels through the blood in three states. A small share circulates unbound and biologically active. Most of the rest is loosely attached to albumin and comes off easily enough to be usable. The remainder is locked tightly to sex hormone binding globulin and is not available to tissue. A total testosterone assay adds all three together and reports one figure.
This is why a total can look reassuring while a man is symptomatic. If SHBG is high, the total is propped up by hormone that is bound and unusable. Total testosterone alone cannot distinguish that situation, which is why SHBG and free testosterone are drawn alongside it rather than after it.
Testosterone follows a daily rhythm. It peaks in the early morning and falls across the day, and in younger men the difference between the morning peak and the afternoon trough can be large enough on its own to move a man across a diagnostic threshold. Drawing before 10am is what makes one result comparable to another. Mass spectrometry is preferred over older immunoassays, which lose accuracy at the low end of the range, which is exactly the range that decides whether a man is diagnosed.
Why it is on the panel
It is the entry point for the entire androgen question and the measurement every treatment guideline is written around. Diagnostic thresholds, the decision to treat, and the targets treatment aims at are all expressed in total testosterone. Nothing else on the panel replaces it. It is simply not sufficient on its own.
Interpretation
Reading the result
Reference ranges vary between laboratories and the range printed on your report is the one that applies to your sample. The bands below are the ones used in practice for adult men.
A number is not a diagnosis, and a single number is not even a measurement you can act on. Low testosterone is a clinical diagnosis requiring both a confirmed low measurement and symptoms consistent with it. Men with numbers in the 200s and no symptoms exist, and men in the 400s who feel dreadful for a reason the rest of the panel finds also exist.
What moves the number without any disease being present
Several of these are common enough that repeating a draw under better conditions resolves the question entirely, with no treatment involved.
What happens next
A single low result is repeated on a second morning before anything is called a diagnosis.
If both are low, LH and FSH separate a testicular cause from a pituitary or hypothalamic one. That distinction changes the treatment entirely.
If the pattern points upstream, prolactin and a review of medication follow, because a pituitary cause and an opioid cause look identical on a testosterone result alone.
If the result is normal, the rest of the panel is where the answer usually is. Thyroid, iron, glucose, vitamin D, sleep and mood account for most of the symptoms that bring men in.