Best time of day to test testosterone

Testosterone changes over the day, so a result depends partly on when the blood was drawn. Morning draws are the standard, and the sources below say why.

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What the sources say

MedlinePlus says a provider takes the blood sample in the morning, between 7 and 10, because testosterone levels are typically highest then (MedlinePlus).

The Endocrine Society guideline recommends “fasting morning total T” as the first test for diagnosing low testosterone, and a repeat of the same measurement to confirm (Bhasin et al., 2018).

How large the time-of-day gap is

A study of 66 men aged 30 to 80 drew blood at three morning and three afternoon visits. In men aged 30 to 40, testosterone was 20 to 25% lower at 4 pm than at 8 am. The gap shrank with age, to about 10% at age 70 (Brambilla et al., 2009).

Among men with at least one result under the study’s low cut-off of 300 ng/dL after noon, five of eight aged 30 to 47 and four of nine aged 66 to 80 had normal results at all three morning visits. The authors concluded that testosterone measurements should be limited to morning hours in both younger and older men. The 300 ng/dL figure is that study’s cut-off. It is not a rule for diagnosing you.

Other hormones

In the same study, DHT, SHBG, LH, FSH and estradiol varied much less across the day, and the authors said sampling through the day is appropriate for them. If you order a panel, your order may still carry its own timing and fasting instructions. Follow those.

What this means when you book

• Choose the earliest slot that suits you. Draw sites keep their own hours, so check the hours listed on your order before you go.
• If a draw has to happen later in the day, note the time. In the study above, afternoon results ran lower than morning ones, so the two may not match.
• Eating can also lower a result. One study found a 25% average fall after a sugar drink (Caronia et al., 2013). See fasting before a testosterone test.
• The guideline describes the confirming test as a repeat of the same measurement: morning and fasting. See retesting.

What timing can’t fix

A well-timed draw gives a cleaner number. It does not diagnose anything. MedlinePlus says a testosterone level test alone can’t diagnose a condition, and that results can mean different things depending on the test, your age and your symptoms. Talk to a clinician about your results and any symptoms.