"Your testosterone level is 11 nmol/L" — now what? For many men, the real confusion begins after the lab result. Reference ranges are wide, interpretation is complex, and different doctors give different recommendations. In this article, we explain the most important laboratory parameters related to testosterone, when therapy is medically indicated, and why diagnosis always consists of two parts: laboratory values and clinical symptoms.
Total testosterone: The first indicator
The most commonly measured value is total testosterone. It encompasses three fractions:
- SHBG-bound testosterone (~60–70%): Bound to sex hormone-binding globulin (SHBG) and biologically inactive
- Albumin-bound testosterone (~25–35%): Loosely bound, easily released, and considered bioavailable
- Free testosterone (~1–3%): Unbound and immediately biologically active
Reference ranges
Exact reference values vary by laboratory and measurement method. The most common guidelines use the following thresholds:
| Classification | nmol/L | ng/dL |
|---|---|---|
| Clear deficiency | < 8 | < 230 |
| Gray zone | 8–12 | 230–350 |
| Normal range | 12–35 | 350–1000 |
| Upper normal range | > 25 | > 720 |
Note: These values serve as guidelines. What is "normal" also depends on age, physical condition, and individual well-being. A 30-year-old with a value at the lower end of the reference range may be significantly more symptomatic than a 65-year-old with the same value.
Conversion factor
Many labs report testosterone in different units. The conversion: 1 nmol/L = 28.84 ng/dL. If your lab result is in ng/dL, divide by 28.84 to get nmol/L. Always use the same unit when comparing results over time.
Why total testosterone alone isn't enough
Total testosterone is an important first indicator but has significant limitations. The reason: SHBG levels vary widely and influence how much of the measured testosterone is actually biologically active.
What increases SHBG (higher total T, but less free T)
- Age — SHBG rises by an average of 1–2% per decade of life
- Liver diseases (hepatitis, cirrhosis)
- Hyperthyroidism (overactive thyroid)
- Medications: Antiepileptics, certain antibiotics
- Extreme underweight
What lowers SHBG (lower total T, but potentially normal free T)
- Overweight/obesity
- Insulin resistance/type 2 diabetes
- Hypothyroidism (underactive thyroid)
- Androgens/anabolic steroids
- Nephrotic syndrome
What this means in practice
An overweight patient may have a total testosterone of 10 nmol/L — which would suggest a deficiency. However, his SHBG is also low due to the excess weight, so his free testosterone may be completely normal. Without measuring free testosterone or SHBG, he could incorrectly receive a TRT diagnosis.
Conversely, a slim, older patient may have a total testosterone of 14 nmol/L — nominally "normal." However, his SHBG is elevated due to age, and his free testosterone falls below the critical threshold. Despite "normal" total T, he has a clinically relevant deficiency.
Free testosterone: The more precise measure
Free testosterone is the biologically active fraction and the more meaningful measurement. Unfortunately, direct measurement is methodologically challenging and error-prone (many commercially available assays are inaccurate) [1].
Gold standard: Equilibrium dialysis
The most accurate method is equilibrium dialysis, but it is complex and expensive. In practice, free testosterone is therefore usually calculated — based on total testosterone, SHBG, and albumin. The Vermeulen formulas or ISSAM online calculators provide reliable results [1]. So-called bioavailable testosterone (free + albumin-bound) is another useful parameter that some laboratories report as an alternative to free testosterone.
Free testosterone reference ranges
| Classification | pmol/L | pg/mL |
|---|---|---|
| Deficiency | < 220 | < 6.5 |
| Gray zone | 220–300 | 6.5–9.0 |
| Normal range | > 300 | > 9.0 |
Which other lab values should be measured
Testosterone is not evaluated in isolation. A complete hormone panel additionally includes:
LH and FSH — The signaling hormones
How are your testosterone levels?
Our doctor-developed self-test shows you in 4 minutes whether an evaluation could be useful — free and anonymous.
- Low + low testosterone → Secondary hypogonadism (problem in the brain: hypothalamus or pituitary gland)
- High + low testosterone → Primary hypogonadism (problem in the testes)
- This distinction is clinically crucial, as it identifies the cause of the deficiency and influences treatment approach
Estradiol (estrogen)
The most important estrogen in men. Formed from testosterone via the enzyme aromatase. Values that are too high can cause symptoms (gynecomastia, water retention), while values that are too low are also problematic (bone density, libido). Important as a baseline and for therapy monitoring.
Prolactin
Elevated prolactin can suppress testosterone and indicates a possible pituitary tumor (prolactinoma). Must always be measured in secondary hypogonadism.
Thyroid values (TSH, fT3, fT4)
Thyroid disorders can mimic numerous symptoms of testosterone deficiency and should be excluded as a differential diagnosis.
Blood count, liver values, lipid profile
Essential as a baseline before possible therapy and for monitoring during TRT. Details can be found in our blood work guide.
The "gray zone": Values between 8 and 12 nmol/L
Most discussions and uncertainties arise in the gray zone — values that are neither clearly pathological nor clearly normal. Here, clinical symptoms become the decisive factor [3].
When therapy in the gray zone makes sense
- Several typical symptoms are present (exhaustion, loss of libido, cognitive impairment)
- Lifestyle factors have already been optimized (sleep, nutrition, exercise, weight)
- Free testosterone is also in the lower range or below normal
- No contraindications (untreated sleep apnea, active prostate cancer, uncontrolled polycythemia)
When a wait-and-see approach is appropriate
- Symptoms are mild or nonspecific
- Lifestyle factors have not yet been addressed (obesity, sleep deprivation, stress)
- Free testosterone is normal
- Patient has no significant impairment
Correct blood collection: Practical tips
Testosterone measurement is susceptible to errors. Improperly performed blood draws can lead to distorted results — both falsely high and falsely low values.
Checklist for accurate measurement
- Morning between 7:00 and 10:00 AM — Testosterone follows a circadian rhythm and peaks in the morning
- Fasting — Food can affect SHBG levels and thereby the result
- No exercise the previous day — Intense training can temporarily elevate levels
- No alcohol in the 48 hours before measurement
- Normal night's sleep — Poor sleep can lower values by up to 15%
- Document medications — Opioids, corticosteroids, and certain antidepressants significantly lower testosterone levels
- At least 2 measurements on different days — A single value is never sufficient for a diagnosis [2]
FAQ
At what testosterone level should you consider therapy? With total testosterone below 8 nmol/L (230 ng/dL), a clear deficiency exists. In the gray zone (8–12 nmol/L), clinical symptoms determine the decision: if several typical symptoms are present and lifestyle factors have already been optimized, TRT is medically indicated [2].
What is the difference between total testosterone and free testosterone? Total testosterone encompasses all three fractions in the blood — only 1–3% is biologically active as free testosterone. SHBG binds the majority and renders it inactive. This means total T can be normal while free T is too low — especially in older or lean men with high SHBG [1].
Why must testosterone be measured in the morning while fasting? Testosterone follows a natural daily rhythm: levels are highest in the early morning and drop by 20–30% over the course of the day. An afternoon test could falsely suggest a deficiency that doesn't exist in the morning. Fasting prevents distortions from food-related SHBG changes.
Does a single low testosterone value warrant a diagnosis? No. International guidelines require at least two measurements on different days, as testosterone levels can temporarily drop by up to 50% due to stress, sleep deprivation, illness, or medications. Only repeatedly low values combined with clinical symptoms establish a diagnosis [2].
Conclusion
The question "At what level do I need therapy?" cannot be answered with a simple number. Testosterone diagnostics is an interplay of laboratory values (total T, free T, SHBG, LH, FSH), clinical symptoms, and individual factors such as age, weight, and lifestyle.
A responsible doctor will never recommend TRT based on a single lab value alone — nor refuse treatment when the clinical picture is clear. The best diagnostics combine modern laboratory medicine with a thorough medical history and take the complete clinical context of the individual patient into account. Understanding your own values empowers you to ask the right questions and make a well-informed treatment decision together with your physician.
Further Reading
Specialist in General Internal Medicine · Medical Director
This article was medically reviewed by Dr. Ramadan for accuracy. It is based on current research and international guidelines.
Your Next Step
You've informed yourself — now you can find out in 4 minutes whether a medical evaluation makes sense for you.
Sources
- [1]Vermeulen A, Verdonck L, Kaufman JM (1999). A critical evaluation of simple methods for the estimation of free testosterone in serum. *J Clin Endocrinol Metab*, 84(10), 3666–3672
- [2]Bhasin S et al. (2018). Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. *J Clin Endocrinol Metab*, 103(5), 1715–1744
- [3]Wu FC, Tajar A et al. (2010). Identification of Late-Onset Hypogonadism in Middle-Aged and Elderly Men. *N Engl J Med*, 363(2), 123–135