Testosterone Blood Test: What Gets Tested & Why

If you're considering TRT, your GP will order a comprehensive blood panel — not just a single testosterone reading. Each marker tells a different part of the story, and together they determine whether TRT is appropriate, safe, and likely to help.

Here's what gets tested and why it matters.

Before starting TRT: the diagnostic panel

Total testosterone

The headline number. Measured in nmol/L in Australia. The normal reference range is typically 8–30 nmol/L for healthy adult men, though "normal" varies by age and lab. At least two fasting morning readings are needed — testosterone fluctuates throughout the day and is highest before 10am.

Free testosterone

Only 1–3% of your testosterone circulates freely (unbound). The rest is bound to SHBG and albumin. Free testosterone is the biologically active fraction — the portion that actually enters your cells and produces effects. Some men have "normal" total testosterone but low free testosterone, which can still cause symptoms.

Sex hormone-binding globulin (SHBG)

A protein that binds to testosterone, making it unavailable for use. High SHBG means more testosterone is bound up, even if total levels look fine. SHBG can be elevated by ageing, liver disease, hyperthyroidism, and certain medications.

LH and FSH

Luteinising hormone (LH) and follicle-stimulating hormone (FSH) are produced by the pituitary gland and signal the testes to produce testosterone and sperm. These markers help distinguish primary hypogonadism (testes not responding) from secondary hypogonadism (pituitary not sending the signal). This distinction matters because it affects treatment approach.

Prolactin

Elevated prolactin can suppress testosterone production and may indicate a pituitary issue. It's included in the initial workup to rule out underlying causes before starting TRT.

Oestradiol (E2)

Men produce oestrogen too — primarily through conversion of testosterone via the aromatase enzyme. High oestradiol can contribute to symptoms like fatigue, breast tissue growth, and water retention. It also becomes relevant during TRT monitoring, as testosterone supplementation can increase oestrogen conversion.

Safety markers

Full blood count (haematocrit)

TRT can increase red blood cell production (erythrocytosis). Elevated haematocrit thickens the blood and increases the risk of cardiovascular events. This is one of the most important safety markers during TRT — if haematocrit rises above the acceptable range, your GP will adjust or pause treatment.

PSA (prostate-specific antigen)

A baseline PSA is taken before starting TRT. While TRT does not cause prostate cancer, it can stimulate growth of existing prostate tissue. Regular PSA monitoring ensures any changes are detected early.

Liver function tests (LFTs)

To ensure the liver is functioning normally and can safely process treatment. Some forms of testosterone (particularly oral, which are rarely used in Australia) can affect liver function.

Kidney function

Baseline kidney function (eGFR, creatinine) is included to assess overall health and rule out conditions that may mimic or contribute to low testosterone symptoms.

Lipid profile

Cholesterol and triglycerides are checked because TRT can affect lipid levels. A baseline ensures your GP can monitor for any changes during treatment.

During TRT: monitoring panels

Once on TRT, regular blood work is essential:

• Every 8–12 weeks initially: Testosterone levels, haematocrit, PSA, liver function
• Every 6 months once stable: Comprehensive panel including all initial markers
• Ad hoc: If symptoms change, dose adjustments are made, or side effects appear

How to prepare for a testosterone blood test

• Fasting: 10–12 hours. Water is fine.
• Timing: Before 10am. Testosterone peaks in early morning.
• Repeat: Two separate tests on different days are required for diagnosis.
• Avoid: Heavy exercise the day before, as this can temporarily affect levels.