Blood Tests for Low Testosterone in Australia: What to Ask For and How to Read the Results
Key Takeaways
Which markers to request, when to collect your blood, how to interpret your results, and why afternoon testosterone tests are unreliable. The complete Australian guide.
Why Timing Is Everything
Testosterone follows a diurnal (circadian) rhythm. Levels peak between 7–10am and fall by 20–40% over the day. Healthdirect Australia explicitly states: "It's best to have the blood test early in the morning while you are fasting."
An afternoon sample can produce a result 30% lower than the same man's true morning level. The Endocrine Society's 2018 guidelines require at least two separate morning samples before any diagnosis is made.
Rule: Collect before 10am. Fasting preferred. Always.
The Complete Pre-TRT Blood Panel
Hormonal Markers
Total Testosterone — primary screening measure, reported in nmol/L in Australia. Reference range typically 8–30 nmol/L for adult men. See our testosterone levels by age guide.
Free Testosterone — only ~1–3% of testosterone is biologically active (unbound to SHBG or albumin). Critical when total testosterone is borderline. The Vermeulen formula (JCEM, 1999) is the validated calculation method.
LH and FSH — the pituitary hormones that signal the testes to produce testosterone:
- High LH + Low T = Primary hypogonadism (testicular problem)
- Low/normal LH + Low T = Secondary hypogonadism (pituitary/hypothalamic problem)
SHBG (Sex Hormone-Binding Globulin) — determines how much testosterone is biologically available. High SHBG is common in older men and reduces free testosterone despite normal total testosterone.
Oestradiol — testosterone converts to oestradiol via aromatase. Elevated oestradiol suppresses the HPG axis and causes symptoms including gynaecomastia and mood changes.
Prolactin — a pituitary adenoma (prolactinoma) is a reversible cause of secondary hypogonadism.
Safety Markers
Full Blood Count (FBC) — baseline haematocrit before commencing TRT is essential. Healthdirect Australia lists haematocrit >50% as a contraindication to TRT.
Liver Function Tests — baseline safety; testosterone is metabolised hepatically.
Fasting Lipid Profile and Glucose/HbA1c — baseline metabolic markers, also relevant because testosterone deficiency is associated with insulin resistance.
PSA (Prostate-Specific Antigen) — required for all men over 40 before TRT. Healthy Male confirms PSA testing as standard pre-treatment practice.
The PBS Threshold vs the Clinical Threshold
PBS subsidy (≤5 nmol/L): Qualifies for subsidised Reandron at the standard co-payment via the Pharmaceutical Benefits Scheme.
Clinical treatment threshold (8–12 nmol/L): Men in this range may be symptomatic and appropriate for TRT, but require private scripts. This gap is addressed in the Endocrine Society of Australia's MJA position statement.
Practical Interpretation Table
| Total T (nmol/L) | Interpretation |
|---|---|
| < 5 | Definite deficiency — PBS eligible |
| 5–8 | Probable deficiency — assess free T and symptoms |
| 8–12 | Borderline — free T and clinical context critical |
| 12–20 | Low-normal — investigate other causes |
| > 20 | Normal — low T unlikely the cause |
References
- Bhasin S, et al. Testosterone Therapy in Men with Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2018.
- Vermeulen A, et al. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab. 1999.
- Healthdirect Australia — Testosterone.
- Hormones Australia — Hypogonadism.
- Endocrine Society of Australia — MJA position statement.
- Cleveland Clinic — Low Testosterone.
- Healthy Male — What is TRT?
Ready to speak with an Australian GP about TRT?
Request an appointment with TRT GP Australia — bulk billed through Medicare. No referral required.
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