Key Points
- Testosterone tests should be done in the morning (before 11am)
- Total testosterone is the main test — free testosterone helps interpret borderline results
- SHBG affects how much testosterone is available to your body
- One low result needs confirming with a repeat test
- Results must be interpreted alongside symptoms
The Testosterone Panel
A full testosterone assessment usually includes three tests:
How They Relate
Total Testosterone
All testosterone in your blood — the main measurement
Bound (to SHBG)
~60-70% — Not available for use
Free Testosterone
~2-3% — Active and available
Reference Ranges
These are typical UK laboratory reference ranges. Your lab may use slightly different values.
Total Testosterone
Measured in nmol/L (nanomoles per litre)
| Level | Range (nmol/L) | Interpretation |
|---|---|---|
| Low | Below 8 | Likely deficient |
| Borderline | 8–12 | May need further tests |
| Normal | 12–31 | Within normal range |
Free Testosterone
Measured in pmol/L (picomoles per litre)
| Level | Range (pmol/L) | Interpretation |
|---|---|---|
| Low | Below 180 | May indicate deficiency |
| Normal | 180–740 | Within normal range |
Free testosterone is often calculated rather than directly measured.
SHBG (Sex Hormone Binding Globulin)
Measured in nmol/L (nanomoles per litre)
| Level | Range (nmol/L) | What it means |
|---|---|---|
| Low | Below 18 | More free testosterone available |
| Normal | 18–54 | Within normal range |
| High | Above 54 | Less free testosterone available |
Interpreting Your Results
Low Total Testosterone
- Below 8 nmol/L suggests deficiency
- Needs confirming with repeat test
- Further hormones checked (LH, FSH, prolactin)
- May warrant treatment if symptomatic
Normal Results
- Total T above 12 nmol/L is reassuring
- Symptoms unlikely due to testosterone
- Consider other causes for symptoms
- No treatment usually needed
Borderline (8–12 nmol/L)
- Grey zone — check free testosterone
- Consider SHBG levels
- Symptoms are important
- May need specialist input
Why SHBG Matters
SHBG is a protein that carries testosterone in your blood. It affects how much testosterone is actually available to your body.
High SHBG
- More testosterone is bound and unavailable
- Total testosterone may look normal but free testosterone is low
- Causes: ageing, liver disease, hyperthyroidism, some medications
Low SHBG
- More testosterone is free and available
- Total testosterone may look borderline but free testosterone is adequate
- Causes: obesity, type 2 diabetes, hypothyroidism
The Key Insight
If your total testosterone is borderline (8-12 nmol/L), your SHBG level helps explain whether you truly have deficiency:
- Borderline total + High SHBG → Free testosterone may be low → may need treatment
- Borderline total + Low SHBG → Free testosterone may be adequate → less likely to need treatment
Getting an Accurate Test
To ensure reliable results:
- Test in the morning — before 11am (testosterone peaks early)
- Fasting may be required — check with your GP
- Avoid alcohol — for 24-48 hours before
- Don't test when unwell — illness lowers testosterone temporarily
- Mention all medications — some affect results
Other Hormones Often Checked
If testosterone is low, your GP will usually check these to find the cause:
| Test | Purpose | What it shows |
|---|---|---|
| LH (Luteinising Hormone) | Brain signal to testicles | High = testicle problem, Low = brain/pituitary problem |
| FSH (Follicle Stimulating Hormone) | Sperm production signal | Helps identify the cause |
| Prolactin | Pituitary check | High levels can suppress testosterone |
| Oestradiol | Oestrogen level | Sometimes elevated in obesity |
What Next?
Based on your results:
If Normal
Your symptoms are unlikely due to low testosterone. Consider other causes like depression, poor sleep, or other medical conditions.
If Low or Borderline with Symptoms
- Repeat the test to confirm
- Check for reversible causes (obesity, medications, sleep apnoea)
- May be referred to endocrinology
- Testosterone replacement may be considered
Read our full guide on testosterone and treatment options.