What blood tests do I need to start testosterone Therapy?

Physician-reviewed TRT testing guide

What Blood Tests Do You Need Before Starting TRT?

TRT should not start from symptoms alone or one isolated testosterone result. A good evaluation confirms low testosterone, looks for the cause, establishes safety baselines and identifies issues that may change the treatment plan.

Medically reviewed by Dr. Timothy Mackey
Medical Director · Updated September 2026

Why bloodwork matters before TRT

Blood testing serves four different purposes: confirm that testosterone deficiency is real, determine whether the problem is primarily testicular or hypothalamic/pituitary, establish safety baselines, and identify other conditions that may explain the symptoms.

Fatigue, low libido, erectile dysfunction, reduced strength and mood changes are not specific to testosterone deficiency. Sleep apnea, obesity, thyroid disease, anemia, depression, medications and chronic illness can produce similar complaints.

For the broader diagnostic process, see our low-testosterone testing guide.

1. Total testosterone

Total testosterone is the core biochemical test used to evaluate suspected testosterone deficiency. Major guidelines recommend confirming low testosterone on more than one occasion rather than diagnosing hypogonadism from a single result.

Testing is performed on separate mornings to reduce variability. The Endocrine Society recommends morning fasting measurements; follow the clinician's and laboratory's preparation instructions. Shift workers may need timing tailored to their sleep schedule. Acute illness, sleep disruption, calorie restriction and certain medications can temporarily lower testosterone and affect interpretation.

2. Repeat testosterone testing

If the first testosterone result is low, a second measurement on a separate day is generally recommended before starting long-term therapy. This reduces the chance of labeling a temporary or anomalous result as persistent hypogonadism.

The American Urological Association uses total testosterone below 300 ng/dL as a reasonable diagnostic cutoff, but the diagnosis still requires compatible symptoms or signs and proper confirmation. See our normal testosterone levels guide for the distinction between reference ranges and diagnostic cutoffs.

3. Free testosterone and SHBG

Free testosterone is not required in every patient, but it can be useful when total testosterone is borderline or when sex hormone-binding globulin (SHBG) is likely to be unusually high or low.

Conditions such as obesity, aging, liver disease, thyroid disorders and certain medications can alter SHBG and change the relationship between total and free testosterone. When indicated, free testosterone should be measured by equilibrium dialysis or calculated accurately from total testosterone, SHBG and albumin. Direct analog free-testosterone immunoassays are not recommended by the Endocrine Society.

4. CBC, hemoglobin and hematocrit

A complete blood count is one of the most important safety baselines before TRT because testosterone can stimulate red-blood-cell production and raise hematocrit.

The AUA recommends measuring hemoglobin and hematocrit before treatment. If baseline hematocrit is above 50%, the reason should be evaluated before testosterone is started. During therapy, hematocrit of 54% or higher warrants intervention.

Read our detailed guide to hematocrit on TRT.

5. PSA and prostate assessment

The AUA testosterone-deficiency guideline recommends a baseline PSA in men over 40 before starting TRT. The Endocrine Society emphasizes discussion of prostate-monitoring benefits and risks according to age and risk. The clinician should explain which approach applies to the patient; PSA alone does not exclude prostate cancer.

For men in whom prostate monitoring is appropriate, a baseline PSA can identify findings that need evaluation before treatment and provide a reference for future comparison. An elevated PSA does not automatically mean cancer, but concerning results should be investigated before TRT proceeds.

See TRT and prostate cancer risk.

6. LH: primary vs. secondary hypogonadism

Luteinizing hormone (LH) helps determine whether low testosterone is primarily due to testicular dysfunction or insufficient signaling from the hypothalamus/pituitary.

Low testosterone with elevated LH suggests primary testicular dysfunction. Low testosterone with low or inappropriately normal LH can point toward secondary or functional hypogonadism and may justify additional evaluation. Read how LH and FSH guide the evaluation.

7. Prolactin

Prolactin is particularly useful when testosterone is low and LH is low or inappropriately normal. Persistent hyperprolactinemia can suppress reproductive hormone signaling and may indicate medication effects or pituitary disease.

Markedly abnormal hormone patterns, persistent elevated prolactin, severe headaches or visual symptoms may warrant pituitary imaging or specialist evaluation.

8. FSH and fertility-related testing

Follicle-stimulating hormone (FSH) may be useful when fertility or testicular function is part of the evaluation. However, bloodwork alone cannot determine fertility.

If current or future fertility matters, semen analysis is often more directly informative than serum testosterone. Exogenous testosterone can suppress sperm production, so fertility goals should be discussed before treatment begins. See our TRT and fertility guide.

9. Estradiol

Estradiol testing may be useful in selected men, particularly when breast symptoms, gynecomastia or other estrogen-related concerns are present. It is not necessary to treat every estradiol result or to suppress estrogen routinely in men receiving TRT.

Estradiol has important physiologic roles in male bone and sexual health. Treatment decisions should be based on symptoms and clinical context rather than chasing a single target value.

10. CMP and metabolic testing

A comprehensive metabolic panel is not a diagnostic test for low testosterone, but it can provide useful information about kidney function, liver function, electrolytes and glucose depending on the patient's history and medication plan.

Additional cardiometabolic testing—such as fasting glucose or A1C and a lipid profile—may be appropriate because obesity, diabetes and metabolic disease frequently coexist with low testosterone and can influence treatment risk.

11. Thyroid testing

TSH and other thyroid tests are not mandatory for every TRT patient, but thyroid disease can mimic symptoms such as fatigue, mood changes, weight change and sexual dysfunction. Testing is appropriate when symptoms or medical history raise suspicion.

What testing is not automatically required?

Not every patient needs an exhaustive hormone panel, MRI or ultrasound. Imaging is generally reserved for specific findings—for example, markedly abnormal pituitary hormones, persistent hyperprolactinemia, very low testosterone with concerning secondary features, testicular abnormalities or other clinical indications.

Good medicine means ordering the tests that answer a clinical question rather than ordering every available marker.

What about DHEA, cortisol, DHT or extensive “optimization” panels?

These tests may be useful in selected clinical situations, but they are not routinely required to diagnose testosterone deficiency or begin standard TRT. Broad panels can generate abnormal-looking values that do not change care and may create unnecessary treatment.

Can you start TRT with only one testosterone result?

In most routine cases, that is not consistent with major guideline recommendations. A second appropriately timed measurement is generally used to confirm persistent low testosterone before committing a patient to long-term therapy.

What labs are monitored after TRT starts?

Follow-up commonly includes testosterone levels at timing appropriate to the formulation, CBC/hematocrit and other testing selected for age and risk. PSA/prostate monitoring, estradiol or metabolic testing may be appropriate depending on the patient and treatment plan.

Monitoring should answer whether therapy is effective, whether exposure is appropriate and whether treatment is causing harm—not merely whether the testosterone number increased.

Frequently asked questions

Do I need free and total testosterone before TRT?

Total testosterone is the core test. Free testosterone is most useful when total testosterone is borderline or SHBG is abnormal or likely to distort interpretation.

Do I need PSA before TRT?

The AUA recommends baseline PSA testing in men over 40 before TRT. Discuss your age, prostate risk and the monitoring plan with the clinician.

Do I need estradiol before TRT?

Not necessarily for every man. It can be useful when breast symptoms, gynecomastia or other estrogen-related concerns are present.

Why check LH before testosterone therapy?

LH helps identify whether low testosterone appears to originate primarily at the testes or from hypothalamic/pituitary signaling, which can change the diagnostic workup and treatment options.

Can routine annual bloodwork diagnose low testosterone?

Only if testosterone was actually ordered and measured appropriately. Testosterone is not automatically included in most standard CBC or metabolic panels.

Medical references

• American Urological Association: Testosterone Deficiency Guideline
• Endocrine Society: Testosterone Therapy in Men With Hypogonadism
• MedlinePlus: Testosterone Levels Test

This article is educational and does not replace individualized medical evaluation. The appropriate laboratory panel depends on symptoms, age, fertility goals, medical history and the results of initial testing.