What Blood Test Do You Need For TRT And Why Each Matters

Testosterone replacement therapy (TRT) requires specific blood tests before a prescription is written and at regular intervals after treatment begins. Without the right labs, a provider can't confirm a diagnosis, set a safe dose, or catch problems like rising hematocrit before they become dangerous. Marek Diagnostics offers hormone testing panels built around the markers that the AUA and Endocrine Society recommend at each stage. Men looking to understand their lab results should know that the American Urological Association (AUA) recommends two separate early-morning total testosterone measurements below 300 ng/dL, combined with clinical symptoms, before a diagnosis of testosterone deficiency is made (Mulhall et al., 2018). A single blood draw is not enough.

What blood test do you need for TRT? A standard diagnostic workup commonly includes total testosterone, free testosterone, sex hormone-binding globulin (SHBG), luteinizing hormone (LH), follicle-stimulating hormone (FSH), a complete blood count (CBC) with hematocrit, a metabolic panel, a lipid panel, and prostate-specific antigen (PSA), though providers may tailor testing to the individual client. Each marker plays a different role in confirming the diagnosis, classifying the type of hypogonadism, establishing a safety baseline, and guiding formulation choice. A pre-TRT panel groups these markers into a single order.

Why Are Two Morning Testosterone Draws Required?

Testosterone follows a circadian rhythm, peaking between roughly 7:00 and 10:00 AM and dropping throughout the day. The Endocrine Society's 2018 clinical practice guideline specifies that diagnosis should rest on two separate fasting morning total testosterone values drawn on separate mornings, using the same laboratory assay (Bhasin et al., 2018). This matters because testosterone fluctuates day to day. A single low reading could reflect poor sleep, acute illness, or recent alcohol intake rather than a true deficiency.

The AUA sets the diagnostic threshold at 300 ng/dL (Mulhall et al., 2018). Other guidelines use slightly different cut-offs, and assay variability across laboratories can shift results depending on the platform used, which is why the Endocrine Society recommends a consistent, accurate assay method for both draws.

Eating before the blood draw can lower testosterone readings. Fasting is standard protocol.

What Is the Difference Between Total and Free Testosterone?

Total testosterone measures all circulating testosterone, both protein-bound and unbound. Most circulating testosterone binds to SHBG (with high affinity) or albumin (with lower affinity). Only about 2-4% circulates as free testosterone, the fraction available to act on tissues (Goldman et al., 2017).

In most men, total testosterone alone is enough to confirm or rule out deficiency. Free testosterone becomes important when SHBG is unusually high or low, which distorts the picture. Aging, liver disease, and hyperthyroidism raise SHBG, making total testosterone appear adequate while the biologically available fraction is low. Obesity and insulin resistance lower SHBG, producing a low total testosterone reading even though free testosterone may be within range (Bhasin et al., 2018). Checking both total and free testosterone together, along with SHBG, gives a more complete picture.

Equilibrium dialysis is the gold-standard method for measuring free testosterone. The Endocrine Society considers direct immunoassay methods for free testosterone less reliable, and these assays may misclassify men near the diagnostic threshold.

How Do LH and FSH Help Classify Hypogonadism?

LH and FSH are pituitary hormones that tell the testes to produce testosterone and sperm. When testosterone is low and LH/FSH are elevated, the problem is in the testes (primary hypogonadism). When testosterone is low and LH/FSH are low or inappropriately normal, the signal from the pituitary or hypothalamus is the problem (secondary hypogonadism) (Bhasin et al., 2018).

This distinction matters for treatment. Secondary hypogonadism has reversible causes, including medications (opioids, glucocorticoids), pituitary tumors, hyperprolactinemia, and severe obesity. Identifying a reversible cause before starting TRT may change the treatment approach entirely. Both the AUA and the Endocrine Society recommend checking LH and FSH alongside testosterone testing during the diagnostic evaluation.

A prolactin level is also worth ordering and is available through specialty panels. Markedly elevated prolactin, combined with low LH and FSH, can point to a pituitary adenoma requiring imaging.

Why Is Hematocrit the Most Important Safety Marker on TRT?

Testosterone stimulates erythropoiesis, the production of red blood cells, through its action on the kidneys and bone marrow. Hematocrit, the percentage of blood volume occupied by red blood cells, can rise on TRT, often in a dose-related pattern, though individual responses vary. The Endocrine Society recommends checking hematocrit at baseline, at 3-6 months, and at least annually thereafter (Bhasin et al., 2018). When hematocrit rises above the threshold the Endocrine Society identifies (54%), guideline-based management includes withholding therapy, evaluating for contributing causes such as hypoxia and sleep apnea, and reassessing dosing in consultation with the client.

Intramuscular injections of cypionate or enanthate carry a higher observed rate of erythrocytosis than transdermal gels. A 2018 review found that short-acting injectable formulations carried the highest reported erythrocytosis rates among common TRT delivery methods (Ohlander et al., 2018). Guideline-concordant monitoring includes a complete blood count at baseline and at recommended intervals for all TRT formulations.

Men with a baseline hematocrit already above 50% may be at higher risk and are often candidates for closer monitoring.

What Does Estradiol Reveal During TRT?

A portion of exogenous testosterone converts to estradiol (E2) through the aromatase enzyme. Monitoring estradiol on TRT helps a provider identify excess conversion, which can produce symptoms like fluid retention, breast tissue sensitivity, and mood changes. Providers generally observe higher aromatase activity in men with greater adiposity. This leads to more conversion of testosterone to estradiol.

The sensitive LC/MS-MS assay is preferred for men because the standard immunoassay can overestimate estradiol levels due to cross-reactivity. Neither the AUA nor the Endocrine Society sets a specific estradiol target for men on TRT. Providers generally assess E2 in context, using the ratio of testosterone to estradiol alongside symptoms, rather than treating a lab number in isolation.

What Role Does PSA Play in TRT Monitoring?

Prostate-specific antigen is a screening marker for prostate health. The AUA recommends evaluating PSA before starting TRT, at 3-6 months, and then following standard age-based screening practices (Mulhall et al., 2018). Current evidence does not show that testosterone causes prostate cancer, but because prostate cancer is androgen-responsive, an undiagnosed cancer may grow faster in the presence of exogenous testosterone. The Endocrine Society lists breast or prostate cancer, a palpable prostate nodule or induration, a PSA above 4 ng/mL (or above 3 ng/mL in men at increased risk of prostate cancer) without urological evaluation as contraindications to starting TRT (Bhasin et al., 2018).

A sharp PSA rise (greater than 1.4 ng/mL within 12 months) on TRT warrants referral for urological evaluation.

Which Metabolic and Organ-Function Labs Are Part of a TRT Panel?

A baseline TRT workup extends beyond hormones. Recommended labs include a lipid panel, fasting glucose or HbA1c, and a metabolic panel covering liver and kidney function. The Endocrine Society notes that exogenous testosterone may lower HDL cholesterol and that metabolic parameters should be followed on treatment (Bhasin et al., 2018). A total health panel groups these markers alongside hormone testing in a single order.

Liver function matters in this context because liver disease affects SHBG production and testosterone metabolism. Kidney function is relevant because renal impairment can alter drug clearance. And fasting glucose or HbA1c establishes metabolic baseline, since testosterone deficiency and insulin resistance frequently coexist. Thyroid function (TSH) is also worth checking at baseline. Hypothyroidism can raise SHBG and suppress the hypothalamic-pituitary axis. The result can be a reversible secondary hypogonadism. Tracking these metabolic biomarkers at baseline and on treatment gives the provider a full clinical picture.

The table below summarizes when each test is typically ordered.

How Should Blood Be Drawn When Already on TRT?

Timing the blood draw correctly is just as important as running the right panel. For men on intramuscular cypionate or enanthate, the Endocrine Society recommends measuring testosterone at the midpoint between injections, targeting the mid-normal range (commonly interpreted in clinical practice as approximately 400-700 ng/dL) at that interval (Bhasin et al., 2018). Drawing too close to the injection inflates the result. Drawing right before the next dose shows only the trough. For gels, a blood draw any time after at least 1 week on a stable dose is appropriate. For oral testosterone undecanoate capsules, levels should be drawn 3-5 hours after the morning dose with food, per product labeling. Marek Diagnostics structures follow-up lab panels around each formulation's monitoring schedule.

Men who don't time their draw correctly may end up on the wrong dose. A "low" trough drawn the day before an injection in a man who feels well doesn't mean the dose needs to go up.

What About Cardiovascular Monitoring After the TRAVERSE Trial?

The TRAVERSE trial (5,246 men, ages 45-80, with hypogonadism and preexisting cardiovascular disease or high CV risk) found that transdermal testosterone gel was noninferior to placebo for major adverse cardiovascular events (MACE): 7.0% versus 7.3%, HR 0.96 (Lincoff et al., 2023). The primary cardiac endpoint was neutral. But the testosterone group showed higher rates of atrial fibrillation (3.5% vs 2.4%), pulmonary embolism (0.9% vs 0.5%), and acute kidney injury (2.3% vs 1.5%). TRAVERSE enrolled an older, cardiovascular-risk-enriched population. Whether these findings apply equally to younger or lower-risk men starting TRT is not established.

In February 2025, the FDA issued class-wide labeling changes for all testosterone products: the boxed cardiovascular warning was removed, and a new blood pressure increase warning was added based on ambulatory blood pressure monitoring data (FDA, 2025). Based on these labeling changes, providers are advised to monitor blood pressure during TRT follow-up.

Providers who order pre-built lab panels should confirm that heart health biomarkers, including hematocrit, lipids, and metabolic function, are included.

Understanding which blood tests are part of a TRT workup helps clients engage in a safe, evidence-based treatment process. Every man's panel should be guided by clinical guidelines, timed correctly to the formulation, and repeated at the intervals that the Endocrine Society and AUA recommend. Lab results, alongside symptom assessment, are how a provider evaluates treatment response, catches problems early, and adjusts the plan. The decision to start, adjust, or stop TRT should be made collaboratively between client and provider, guided by lab results, symptoms, risk factors, and individual treatment goals. Marek Diagnostics offers individual biomarker testing and testosterone panels for men at every stage of evaluation and monitoring.

Disclaimer: This blog post is intended for informational purposes only and should not be considered medical advice. Always consult a healthcare professional before making changes to your health routine.

FAQs

What blood test do you need for TRT before starting treatment?

A diagnostic panel for TRT typically includes two separate fasting morning total testosterone measurements, free testosterone, SHBG, LH, FSH, a complete blood count with hematocrit, PSA (age-appropriate), a lipid panel, a metabolic panel covering liver and kidney function, and fasting glucose or HbA1c. The AUA recommends two total testosterone values below 300 ng/dL, combined with symptoms, to confirm a diagnosis of testosterone deficiency (Mulhall et al., 2018).

How often should blood be tested while on TRT?

The Endocrine Society recommends reassessing testosterone, hematocrit, and symptoms at 3-6 months after starting treatment, then at least annually (Bhasin et al., 2018). PSA follows age-based screening guidelines. Lipids and metabolic markers are typically rechecked at 6-12 months and annually thereafter. Many providers add an earlier check at 6-8 weeks after starting or changing a dose.

Why does hematocrit matter during testosterone therapy?

Testosterone stimulates red blood cell production. If hematocrit rises above 54%, the Endocrine Society recommends stopping treatment until the value falls, then restarting at a lower dose (Bhasin et al., 2018). A 2018 review found that short-acting injectable testosterone carried the highest observed erythrocytosis rates among common TRT formulations (Ohlander et al., 2018). Elevated hematocrit is associated with a higher risk of blood clots, though the direct relationship in men on TRT is not fully established.

Can total testosterone be normal while free testosterone is low?

Yes. When SHBG is elevated, more testosterone binds to the protein and less remains available to act on tissues. Conditions that raise SHBG include aging, liver disease, and hyperthyroidism. In these cases, total testosterone may fall within the reference range while free testosterone is below normal. The Endocrine Society recommends measuring free testosterone when total testosterone is near the lower limit or when SHBG is expected to be altered (Bhasin et al., 2018).

What is the best time of day to get blood drawn for TRT labs?

Testosterone peaks in the early morning. For diagnostic testing, fasting blood should be drawn between 7:00 and 10:00 AM. For men already on injectable TRT (cypionate or enanthate), the Endocrine Society recommends drawing blood at the midpoint between injections, targeting the mid-normal range (commonly interpreted in clinical practice as approximately 400-700 ng/dL) at that interval (Bhasin et al., 2018). For gels, blood can be drawn any time after at least 1 week on a stable dose.

Does TRT raise the risk of prostate cancer?

Current evidence does not show that testosterone causes prostate cancer. But prostate cancer is androgen-responsive, meaning an existing undiagnosed cancer may grow in the presence of exogenous testosterone. The AUA recommends checking PSA before starting TRT and during monitoring to catch any significant rise early (Mulhall et al., 2018). A PSA increase greater than 1.4 ng/mL within 12 months on TRT warrants urological evaluation.

References

• Endocr Rev. 2017;38(4):302-324

• FDA Drug Safety Communication. February 28, 2025

• J Clin Endocrinol Metab. 2018;103(5):1715-1744

• J Urol. 2018;200(2):423-432

• N Engl J Med. 2023;389(2):107-117

• Sex Med Rev. 2018;6(1):77-85