Testing testosterone properly: timing, free vs total

Most testosterone results are drawn wrong

The test is cheap, widely sold and routinely mishandled. Before the number means anything, three things have to be true about how it was taken — and a clinic offering treatment off a single afternoon draw has skipped all of them.

The three conditions

• Morning. Testosterone follows a daily rhythm, highest in the early morning and falling through the day, with the swing largest in younger men. Guidelines consistently specify a morning sample, generally before 10am.
• Fasting. Eating — particularly a carbohydrate‑heavy meal — lowers measured testosterone for some hours.
• Twice. A diagnosis of hypogonadism needs two low readings on separate mornings. Day‑to‑day variation is large enough that a single low result is not a finding.

Any acute illness, poor sleep or significant stress in the preceding days also pushes the number down. Testing a man in the week after a chest infection tells you about the infection.

Total, free, and the protein in between

Most testosterone in blood is not available to tissues. It is bound — tightly to sex hormone binding globulin (SHBG), loosely to albumin.

• Total testosterone is everything, bound and free. The standard first test.
• Free testosterone is the small unbound fraction.
• Bioavailable testosterone is free plus the loosely albumin‑bound portion.

This matters because SHBG moves with the very conditions a metabolic clinic treats. Obesity and insulin resistance lower it; ageing, thyroid overactivity and liver disease raise it. A man with low SHBG can have a total testosterone that looks low while his free testosterone is adequate — and the reverse happens too.

So where the total is borderline, or where obesity or thyroid disease is in the picture, total alone is not enough.

How free testosterone should be worked out

There are three routes and they are not equivalent:

• Equilibrium dialysis — the reference method, rarely available outside specialist laboratories.
• Calculated free testosterone, from total testosterone, SHBG and albumin. Inexpensive, reproducible, and what most good practice uses.
• Direct free testosterone immunoassay — the analogue kind is widely criticised as unreliable, and several professional bodies advise against relying on it.

If a clinic quotes you a free testosterone, it is worth asking which of the three it was.

What goes with it, before anything is prescribed

Testosterone is never assessed alone. A proper work‑up also looks at:

• LH and FSH — to separate a testicular problem from a pituitary one, which changes the diagnosis entirely
• Haematocrit, from the full blood count — treatment thickens the blood, and a raised baseline is a reason for caution
• PSA, in older men
• Oestradiol, since testosterone converts to it
• Prolactin, where the picture suggests a pituitary cause

In our costing, the men's hormone additions come to roughly ₡80,000 on top of the baseline. That is not padding; it is the difference between a number and a diagnosis.

The symptom problem

The symptoms attributed to low testosterone — tiredness, low mood, reduced libido, loss of muscle, poor sleep — are also the symptoms of thyroid disease, depression, sleep apnoea, anaemia, and simply being middle‑aged and under‑slept. The overlap is almost total.

That is why the panel around it matters more than the testosterone itself, and why a clinic that tests only testosterone will find testosterone to be the answer.

The boundary

Nothing here says whether you should be tested or treated. Two correctly drawn low results, read alongside the rest of the panel and your symptoms, are where that conversation starts — with a physician, not with a number.