Blood Work for TRT: Which Values Really Matter

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

How is free testosterone obtained? Most Swiss labs do not measure it directly. They calculate it from total testosterone, SHBG and albumin using the method Vermeulen validated in 1999 [3]. So the calculated value is only as reliable as the SHBG behind it: if your report shows free testosterone but no SHBG, ask for it. Details in free vs. total testosterone.

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

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

📋 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

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. The numbers behind it: across 15 randomised trials with 739 treated men and 385 controls, the mean PSA difference versus control was 0.154 ng/mL, and 0.271 ng/mL with intramuscular preparations [7]. The share of men with an elevated PSA afterwards did not differ between the groups. Those trials ran only 3 to 12 months and say nothing about a decade of prostate safety, but they do show that the therapy explains just a small part of the 1.4 ng/mL rise that triggers referral. More in Is TRT safe?.

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.

Hematocrit under testosterone: how much does it actually rise?

Every testosterone preparation raises the mean hematocrit compared with placebo, by roughly 1.4 to 4.3 percentage points depending on the route. The figure comes from a network meta-analysis of 29 randomised placebo-controlled trials with 3,393 men [4].

| Oral testosterone undecanoate | +4.3% | 0.7–8.0 | | Intramuscular enanthate/cypionate | +4.0% | 2.9–5.1 | | Gel | +3.0% | 1.8–4.3 | | Intramuscular undecanoate (depot) | +1.6% | 0.3–3.0 | | Patch | +1.4% | 0.2–2.6 |

Only the gap between intramuscular enanthate/cypionate and the patch reached statistical significance; between the other preparations no difference was demonstrated. The routes were compared through a statistical network rather than head to head, because head-to-head trials do not exist, and the authors call the clinical relevance of the rise an open question [4].

The honest version: a few percentage points are expected on any preparation, the injection sits at the upper end numerically, and "gel is gentler on the blood" is a reasonable assumption rather than a proven fact. Your baseline value matters more than the route. Smokers, men at altitude and men with untreated sleep apnoea start higher and reach 52% sooner. More in TRT side effects and gel vs. injection.

Typical findings and what they mean

Complete blood count or testosterone blood value: what is the difference?

A complete blood count contains no testosterone. It counts red cells, hemoglobin, hematocrit, white cells and platelets, and says nothing about hormones. Asking for a "complete blood count with testosterone" therefore means two separate orders on the request form.

Both belong on the form: the complete blood count delivers the hematocrit that decides whether the dose stays, and the testosterone blood value with SHBG, LH, FSH and estradiol whether the therapy works.

Practical tips for your blood draw

1. Morning, fasting, before 11 AM — always at the same time
2. With injections: draw blood the day before the next injection (trough level)
3. With gel: at least 2 hours after application — or ideally before applying
4. Bring your lab report to the doctor consultation — not just the summary, but the individual values with reference ranges
5. Track your trends: create a simple spreadsheet with date, testosterone, hematocrit, and estradiol — this reveals patterns
6. Consistent conditions: try to always have blood drawn at the same lab at the same time of day — this makes values comparable

Fasting: why breakfast distorts your testosterone blood value

Glucose in the blood pushes testosterone down within minutes. In 74 men aged 19 to 74, a standardised 75 g glucose load lowered mean testosterone by 25% (−4.2 ± 0.3 nmol/L, p < 0.0001), and after two hours the level had still not recovered (13.7 versus 16.5 nmol/L) [5]. Of 66 men with a normal starting value, 10 fell below the hypogonadal threshold of 9.7 nmol/L at least once. SHBG, LH and cortisol stayed unchanged, so the drop is real, not an artefact.

The study used a glucose solution, not a croissant with coffee, so nobody can price your breakfast in nmol/L. It does justify the instruction: come fasting, and have a low non-fasting result repeated fasting before anyone draws conclusions.

Time of day: why the draw belongs before 11 AM

In a survey of men with a mean age of 61, total testosterone averaged 411.7 ng/dL between 8 and 11 AM against 368.3 ng/dL outside that window (p = 0.0003), and the gap held after adjustment for age and BMI [6]. Between 2 and 5 PM the mean was 344.3 ng/dL, between 5 and 8 PM 334.4 ng/dL, both significantly lower.

Two caveats: each man was measured once, so different men were compared at different times, and at 61 the circadian rhythm is already flattened. The 20 to 30% spread quoted earlier applies to younger men with a pronounced rhythm; older men show the smaller gap measured here. Neither argues for stretching the window. Book before 11 AM, always the same slot.

Testosterone blood test at your family doctor: what to ask for

Yes, your family doctor can order every one of these values, and that is usually the fastest route. What decides the quality of the result is not who holds the needle but which values are on the request form.

Hand over a written list: total testosterone, SHBG, LH, FSH, estradiol, complete blood count with hematocrit, PSA from age 40, liver values, creatinine, lipids and HbA1c. Put the timing on the slip too, because a form without "before 11 AM, fasting" tends to come back as an afternoon appointment. Our lab values page prints out for exactly this.

With a documented indication, basic insurance (OKP) covers the tests, deductible and co-payment as usual (health insurance and TRT). Prefer the whole panel ordered and interpreted in one place? Start with our self-test.

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.

Does a complete blood count include testosterone? No. It covers red cells, hemoglobin, hematocrit, white cells and platelets, and contains no hormone values. Testosterone must be ordered as a separate assay, ideally with SHBG, LH, FSH and estradiol [1].

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

• Blood Test for TRT in Zürich — Labs & Walk-in
• Blood Test for TRT in Bern — Labs & Walk-in