You may have heard that testosterone therapy requires regular monitoring. But which values are actually measured? What do the numbers mean? And when is a value "too high" or "too low"?
This blood work guide explains all relevant lab values — before starting therapy and throughout treatment. No medical degree required.
Before therapy: The comprehensive baseline panel
Before TRT can even begin, comprehensive blood work must be performed. This serves two purposes: first, to confirm the diagnosis, and second, to ensure no contraindications exist [1].
Core values: Testosterone and related hormones
| Value | What it shows | Normal range | Why important |
|---|---|---|---|
| Total testosterone | All testosterone in the blood | 10–35 nmol/L | Foundation of diagnosis |
| Free testosterone | The actually available fraction | 225–725 pmol/L | More meaningful than total T |
| SHBG | Binding protein that "holds" testosterone | 10–70 nmol/L | Explains discrepancies between total T and free T |
| LH | Signaling hormone from the brain | 1.5–9 IU/L | Shows whether the problem is in the testes or the brain |
| FSH | Signaling hormone for sperm production | 1.5–12 IU/L | Important for fertility assessment |
| Estradiol (E2) | Estrogen in men | 40–160 pmol/L | Too much can cause breast tenderness |
Why measure in the morning? Testosterone follows a natural circadian rhythm: levels are highest in the morning and lowest in the evening. A blood test at 4 PM can read 20–30% lower than one at 8 AM — without anything having actually changed. That's why the rule is: blood draw always before 11 AM, fasting [1].
Why two measurements? A single low reading is not enough for a diagnosis. Guidelines require at least two measurements on different days to rule out fluctuations from stress, sleep, or illness [1]. Acute stress, sleep deprivation, or infection can temporarily lower testosterone by up to 50% — making a single low value unreliable.
Safety values: What must be ruled out
| Value | What it shows | Normal range | Why before TRT? |
|---|---|---|---|
| Hematocrit | Red blood cell proportion | 40–52% | TRT can increase it — baseline is crucial |
| Hemoglobin | Oxygen carrier in blood | 13–17 g/dL | Assessed together with hematocrit |
| PSA | Prostate marker | < 4 ng/mL | Rule out prostate cancer before TRT |
| Liver values (ALT, AST) | Liver function | < 50 U/L | Safety check |
| Creatinine | Kidney function | 60–120 µmol/L | Safety check |
| Lipid profile | Cholesterol, triglycerides | Individual | TRT affects blood lipids |
| HbA1c / Fasting glucose | Diabetes risk | < 5.7% / < 5.6 mmol/L | Diabetes and testosterone are interconnected |
Why are these safety values so important? Some serve not only as safety checks but provide crucial clues about the cause of testosterone deficiency. An elevated HbA1c, for example, indicates insulin resistance — one of the most common comorbidities in men with low testosterone. In many cases, treating the underlying condition (e.g., weight loss for metabolic syndrome) also improves testosterone levels, potentially making TRT unnecessary [1].
Additional investigations when indicated
In certain cases, the doctor will order further tests:
- Prolactin: Elevated levels may indicate a pituitary adenoma (benign brain tumor) causing secondary hypogonadism
- Thyroid values (TSH, fT3, fT4): Thyroid disorders can mimic testosterone deficiency symptoms
- Ferritin/Iron: Iron overload (hemochromatosis) can damage the testes and is a treatable cause of hypogonadism
- Cortisol: Adrenal disorders can present similarly to testosterone deficiency
During therapy: What gets monitored and when
Once TRT is started, monitoring begins — regular blood checks to ensure the therapy is working and no problems arise [2].
The monitoring schedule
| Period | Interval | What is measured |
|---|---|---|
| Years 1–2 | Every 3 months | Testosterone (trough level), hematocrit, estradiol, PSA |
| From year 3 | Every 6 months | Testosterone, hematocrit, estradiol, PSA, lipid profile |
| Annually | Additionally | Complete blood count, lipid profile, liver values, fasting glucose |
📋 Practical reference: The complete list of all required lab values — to show your family doctor or walk-in lab — can be found on our lab values page.
What does the doctor watch most closely?
1. Hematocrit — the most important safety value
How are your testosterone levels?
Our doctor-developed self-test shows you in 4 minutes whether an evaluation could be useful — free and anonymous.
Testosterone stimulates red blood cell production (erythropoiesis). This is fundamentally positive — but too much of a good thing makes the blood "thicker" and increases thrombosis risk. When hematocrit exceeds 52%, the dose is adjusted. Above 54%, action is required — through dose reduction, switching to gel, or therapeutic phlebotomy (blood donation) [2]. Patients who smoke or live at high altitude already have elevated baseline values and should be monitored more closely.
2. Estradiol — maintaining balance
When too much testosterone is converted to estrogen (via the enzyme aromatase), it can cause breast tenderness, water retention, or mood swings. Values above 160 pmol/L should raise attention. Often a dose adjustment helps; in rare cases, the doctor prescribes an aromatase inhibitor. Men with higher body fat have more aromatase activity and are therefore more prone to elevated estradiol levels.
3. PSA — keeping an eye on the prostate
PSA is monitored before and throughout TRT. A slight increase under TRT is normal and expected. Concerning is a rise of more than 1.4 ng/mL within one year or an absolute value above 4 ng/mL — this triggers urological evaluation [1]. Current meta-analyses confirm that TRT does not increase prostate cancer risk, but existing tumors may grow faster.
4. Trough levels — testosterone at its lowest
With injection therapy, testosterone levels fluctuate between injections. The measurement is taken at the trough level — just before the next injection. This should be in the lower normal range (at least 12–15 nmol/L), not below. If the trough level is significantly below 12 nmol/L, either the dose is too low or the injection interval is too long.
Typical findings and what they mean
| Finding | Possible cause | What to do? |
|---|---|---|
| Testosterone too low despite TRT | Dose too low or poor absorption | Increase dose or switch delivery method |
| Hematocrit > 52% | Normal TRT response, but excessive | Reduce dose, switch to gel |
| Estradiol > 160 pmol/L | Excessive conversion (aromatase) | Adjust dose, consider aromatase inhibitor |
| LH/FSH very low on TRT | Expected! TRT suppresses own production | Normal, no action needed |
| PSA increase > 1.4 ng/mL/year | Prostate evaluation needed | Urology referral |
Practical tips for your blood draw
- Morning, fasting, before 11 AM — always at the same time
- With injections: draw blood the day before the next injection (trough level)
- With gel: at least 2 hours after application — or ideally before applying
- Bring your lab report to the doctor consultation — not just the summary, but the individual values with reference ranges
- Track your trends: create a simple spreadsheet with date, testosterone, hematocrit, and estradiol — this reveals patterns
- Consistent conditions: try to always have blood drawn at the same lab at the same time of day — this makes values comparable
FAQ
Which blood values must be tested before starting TRT? Before starting therapy, you need at minimum: total testosterone, free testosterone, SHBG, LH, FSH, estradiol, hematocrit, hemoglobin, PSA, liver values, and lipid profile. All values must be measured fasting before 11 AM on two separate days [1].
How often do I need blood work during TRT? In the first 1–2 years, every 3 months. From the third year with stable values, every 6 months. Once yearly a complete blood count with lipid profile and liver values. If your doctor checks less frequently, you should ask why.
What happens if my hematocrit gets too high on TRT? A hematocrit above 52% requires dose adjustment. Above 54%, active intervention is needed — through dose reduction, switching from injections to gel, or therapeutic phlebotomy (blood donation). An excessively high hematocrit increases the risk of blood clots and stroke [2].
Can my general practitioner perform TRT blood work? Yes. Blood draws can be done by any GP or walk-in lab. Costs are typically covered by basic health insurance (OKP) in Switzerland. Important: provide your GP with a clear list of the required values.
Conclusion
Blood work monitoring is the foundation of safe TRT. Without regular monitoring, you're flying blind. The good news: only a few values truly matter — testosterone, hematocrit, estradiol, and PSA. An experienced doctor knows exactly what to watch for.
If a doctor prescribes TRT but offers no structured monitoring — find a different doctor.
Further Reading
- TRT Side Effects Honestly Explained
- At What Testosterone Level Is Therapy Worthwhile?
- Is TRT Safe? What Science Really Says
Blood Tests in Your Canton
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]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
- [2]Lincoff AM et al. (2023). Cardiovascular Safety of Testosterone-Replacement Therapy. *N Engl J Med*, 389(2), 107–117
- [3]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