How Is Low Testosterone Diagnosed? Tests and What They Mean

Medically reviewed by Meg LaFerriere, APRN · Regulate Rx, Lee’s Summit, MO

A single testosterone result on a patient portal can be confusing, or misleading. Guidelines set a higher bar for a reason.

What do guidelines require to diagnose low T?

The American Urological Association (AUA) 2018 guideline and the Endocrine Society agree on the core rule. You need both symptoms or signs of testosterone deficiency and consistently low blood levels.

That means at least two total testosterone tests, drawn on different days, in the early morning. Testosterone peaks in the morning and dips later in the day. Illness, poor sleep and even a recent heavy meal can lower a reading, so a single low result isn’t a diagnosis.

The AUA uses a total testosterone below 300 ng/dL as a reasonable cutoff for low levels, while recognizing that each lab’s reference range is a little different.

Which blood tests are part of a testosterone workup?

Total testosterone is the starting point. Depending on your results and history, your practitioner may add other tests.

Lab	Why it may be checked
Total testosterone (x2, morning)	Confirms whether levels are low
Free testosterone and SHBG	Helpful when total T is borderline or SHBG may be high or low
LH and FSH	Shows whether the problem starts in the testes or the pituitary
Prolactin	Screens for a pituitary cause when LH is low or normal
Estradiol	Checked if you have breast tenderness or enlargement
CBC / hematocrit	Baseline before treatment, since testosterone can raise red blood cells
PSA	Prostate baseline, typically for men over 40 before starting therapy

Why does it matter if LH is high or low?

LH (luteinizing hormone) is the pituitary’s signal telling the testes to make testosterone. It helps sort low T into two broad types:

• Primary: the testes aren’t responding. Testosterone is low and LH is usually high.
• Secondary: the brain’s signal is low. Testosterone is low and LH is low or inappropriately normal. Obesity, opioids, high prolactin and pituitary conditions are possible causes.

This difference changes the next steps. Some men need imaging or a referral to endocrinology, and the type of low T can affect fertility options.

How should you prepare for a testosterone blood test?

A few simple habits make your results more reliable:

• Schedule the draw in the early morning, ideally before 10 am.
• Avoid testing while you’re sick or right after a night of very poor sleep.
• Tell your practitioner about all medications and supplements, including any testosterone or “boosters.”
• Repeat the test on a second morning if the first is low.

If you already use testosterone, the timing of your draw relative to your last dose matters. Your practitioner will tell you when to test.

What happens after your labs come back?

Results are reviewed together with your symptoms, exam and medical history. If two morning tests confirm low testosterone and the cause is clear, you can talk through whether treatment makes sense for you, including fertility goals, prostate history and sleep apnea risk.

If levels are normal, that’s useful too. It points the search toward sleep, thyroid, mood, metabolic health or medications instead. At Regulate Rx in Lee’s Summit, testing is the first part of our men’s hormone program, and pricing for labs is listed on our pricing page.

Frequently asked questions

Can I be diagnosed with low T from one blood test?

Not according to guidelines. Testosterone varies from day to day, so the AUA and Endocrine Society call for two separate early-morning tests along with symptoms before confirming a diagnosis.

Is free testosterone more accurate than total testosterone?

Total testosterone is the standard first test. Free testosterone is most helpful when total levels are borderline or when SHBG is likely abnormal, such as with obesity, aging, thyroid issues or certain medications.

Do I need a PSA test before testosterone therapy?

Guidelines recommend checking PSA in men over 40 before starting testosterone, and monitoring it during treatment. Your practitioner may also ask about urinary symptoms and family history of prostate cancer.

Sources: American Urological Association 2018 Testosterone Deficiency Guideline; Endocrine Society Clinical Practice Guideline on Testosterone Therapy in Men with Hypogonadism (2018); Cleveland Clinic; NIH/MedlinePlus

This article is for general education and isn’t medical advice. Treatments aren’t right for everyone, and results vary. Our practitioner reviews your health history before any treatment.