Total Testosterone vs Free Testosterone
Total testosterone is usually the first blood test used to assess possible testosterone deficiency. It measures testosterone that is both protein-bound and unbound in the bloodstream. Free testosterone is the small fraction not bound to proteins and may be useful when total testosterone is borderline or when sex hormone-binding globulin (SHBG) is abnormal. Neither test should be interpreted from a single random blood sample or without symptoms.
What is total testosterone?
Most testosterone in blood is attached to proteins, mainly SHBG and albumin. Total testosterone measures all circulating testosterone together. Because guideline thresholds and most clinical evidence are based on total testosterone, it is generally the starting test.
What is free testosterone?
Free testosterone is the small unbound fraction that can enter tissues readily. It can be measured by specialised methods or calculated from total testosterone, SHBG and albumin. The method matters: calculated free testosterone is commonly used when SHBG is abnormal, while poorly validated direct ‘free testosterone’ immunoassays can be misleading and should not be interpreted as interchangeable with reliable methods.
Total testosterone vs free testosterone
| Feature | Total testosterone | Free testosterone |
|---|---|---|
| What it measures | Bound plus unbound circulating testosterone | The small unbound fraction |
| Usual role | First-line test for suspected hypogonadism | Second-line aid when total T is borderline or SHBG is abnormal |
| Affected by SHBG | Yes | Less directly, but calculation depends on SHBG |
| Guideline thresholds | Commonly defined | Assay and calculation methods vary more |
| Best interpreted with | Symptoms, morning timing and repeat testing | Total T, SHBG, symptoms and assay method |
What is SHBG and why does it matter?
Sex hormone-binding globulin is a protein that carries testosterone in blood. When SHBG is unusually low or high, total testosterone can give an incomplete picture of biologically available androgen.
- SHBG is often lower in obesity and insulin resistance.
- SHBG may be higher with ageing, some liver conditions, hyperthyroidism and certain medicines.
- Because SHBG varies, a borderline total testosterone may need free testosterone assessment rather than an automatic diagnosis.
When is free testosterone especially useful?
- Total testosterone is near the laboratory or guideline threshold.
- Obesity or metabolic disease may have lowered SHBG.
- A condition or medicine is likely to raise SHBG.
- Symptoms strongly suggest hypogonadism but total testosterone is not clearly low.
- Total testosterone appears low but the clinical picture does not fit.
Which number is “more important”?
There is no universal answer. Total testosterone remains the standard first-line test because it is better standardised and most guideline thresholds are based on it. Free testosterone becomes most useful when SHBG is likely to distort the total value or the symptoms and total testosterone do not fit neatly together; it is a problem-solving test, not automatically the ‘better’ number.
What testosterone level is considered low?
Thresholds differ between guidelines. The AUA considers total testosterone below 300 ng/dL a reasonable cut-off when compatible symptoms are present. EAU guidance commonly uses 12 nmol/L, approximately 346 ng/dL, as a diagnostic threshold for further assessment. Laboratory methods and clinical context matter, so a single borderline result should not be labelled as disease.
How should the blood test be done?
EAU guidance recommends fasting morning total testosterone, generally between 7:00 and 10:00 AM, with confirmation of a low result on another day. Acute illness, poor sleep, food intake and some medicines can affect the result.
What happens after a low result?
- Repeat the morning total testosterone.
- Review symptoms and examination findings.
- Check LH and FSH to identify primary versus secondary hypogonadism.
- Consider prolactin when appropriate.
- Measure SHBG and calculate free testosterone if the total result is borderline or SHBG may be abnormal.
- Look for reversible causes such as obesity, poor sleep, illness or medication effects.
When should you see a urologist or andrologist?
Seek assessment if you have repeated low or borderline testosterone, low libido, reduced morning erections, infertility or uncertainty about conflicting total and free testosterone reports. Bring the original laboratory reports because assay method, units and timing matter.
Emergency warning signs
An abnormal testosterone report is rarely an emergency. Seek urgent care for sudden severe headache with visual symptoms, acute testicular pain or swelling, chest pain or other severe acute illness.
What to bring for consultation
- Total and free testosterone reports with units and collection times.
- SHBG and albumin if tested.
- LH, FSH, prolactin and thyroid reports if available.
- Medication and supplement list.
- Information about libido, erections, fertility and sleep.
FAQs
Should I test free testosterone instead of total testosterone?
Usually no. Total testosterone is normally the first test. Free testosterone is added when the total result or SHBG makes interpretation uncertain.
Is a direct free testosterone test always accurate?
No. Free-testosterone assays vary in quality. Guidelines favour accurate methods and often use calculated free testosterone based on total testosterone and SHBG when appropriate.
Can total testosterone be low while free testosterone is normal?
Yes, particularly when SHBG is low, as can occur in obesity. This is one reason borderline results require clinical interpretation.
Can total testosterone be normal while free testosterone is low?
It can occur when SHBG is high. If symptoms are convincing, SHBG and calculated free testosterone may clarify the result.
Related reading
- Morning Testosterone Test: Why Timing Matters
- Low Testosterone in Men: Symptoms and Treatment
- Belly Fat and Low Testosterone
- Diabetes and Low Testosterone
- Low Libido in Men: Causes and Treatment
- Urologist in Latur
References
- European Association of Urology. EAU Guidelines on Sexual and Reproductive Health, 2026 – Male Hypogonadism https://uroweb.org/guidelines/sexual-and-reproductive-health/chapter/male-hypogonadism
- American Urological Association. Evaluation and Management of Testosterone Deficiency: AUA Guideline https://www.auanet.org/Documents/Guidelines/PDF/Testosterone%20Website%20Final%280%29.pdf
- Bhasin S, Brito JP, Cunningham GR, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2018 https://www.endocrine.org/clinical-practice-guidelines/testosterone-therapy