Introduction: Who Should Consider Testing for Primary Hypogonadism

Not every man needs to be tested for primary hypogonadism, but certain signs should prompt a conversation with a healthcare provider. Men who experience a noticeable decrease in sexual desire, difficulty achieving or maintaining erections, unexplained fatigue, or mood changes like depression or irritability may benefit from evaluation.^[1] These symptoms can appear at any age, though they become more common as men grow older.

Physical changes also serve as important clues. If a man notices his muscle mass declining despite regular activity, an increase in body fat, loss of body or facial hair, or breast tissue development, these could signal low testosterone production.^[7] Men with smaller-than-expected testicles or those who have experienced testicular injury, infection, or exposure to chemotherapy or radiation should also consider evaluation, as these factors directly damage the organs responsible for hormone production.^[3]

In younger men, delayed puberty is a red flag. If a boy hasn’t begun developing typical male characteristics—such as deepening voice, muscle growth, or genital development—by the expected age, diagnostic testing can help determine whether the testicles are functioning properly.^[4] Men with certain genetic conditions, such as Klinefelter syndrome (a condition where a male is born with an extra X chromosome), are at high risk and should undergo screening even if symptoms are subtle.^[2]

It’s also important to recognize that some medical conditions increase the likelihood of hypogonadism. Men with obesity, type 2 diabetes, chronic kidney disease, liver cirrhosis, or HIV/AIDS are at greater risk and may benefit from routine screening, even if they don’t report obvious symptoms.^[12] Healthcare providers may suggest testing for these individuals as part of ongoing management of their primary condition.

Diagnostic Methods: How Primary Hypogonadism Is Identified

Blood Tests for Testosterone Levels

The cornerstone of diagnosing primary hypogonadism is measuring testosterone in the blood. Because testosterone levels naturally fluctuate throughout the day—peaking in the early morning and declining as the day progresses—blood samples are typically collected between 8 and 10 a.m.^[9] This timing ensures the most accurate reflection of a man’s testosterone production.

The test measures total testosterone, which includes both the hormone bound to proteins in the blood and the small amount that circulates freely. According to the American Urology Association, a total testosterone level below 300 nanograms per deciliter (ng/dL) is generally considered low, though some experts believe levels below 250 ng/dL should be the threshold.^[7] Because a single test result can be influenced by temporary factors such as illness, stress, or poor sleep, the diagnosis should not be made based on one measurement alone.

A second morning blood test is recommended to confirm the finding.^[2] Only when two separate tests show low testosterone, and the patient reports symptoms consistent with hypogonadism, should the diagnosis be considered reliable. Some laboratories may also measure free testosterone—the portion of the hormone not bound to proteins—which provides additional insight into how much testosterone is actually available for the body to use.^[19]

Distinguishing Primary from Secondary Hypogonadism

Once low testosterone is confirmed, the next step is to determine whether the problem originates in the testicles (primary hypogonadism) or in the brain’s control centers (secondary hypogonadism). This distinction is crucial because it affects both treatment decisions and the search for underlying causes.^[2]

Doctors measure levels of luteinizing hormone (LH), a hormone released by the pituitary gland in the brain that signals the testicles to produce testosterone. In primary hypogonadism, the testicles are damaged or not functioning properly, so the brain tries to compensate by producing more LH. As a result, LH levels are typically elevated—often above 10 ng/mL.^[14] This pattern confirms that the testicles themselves are the source of the problem.

If LH levels are low or normal despite low testosterone, this suggests the issue lies in the brain’s signaling system, indicating secondary hypogonadism rather than primary.^[3] This difference has important implications: primary hypogonadism usually cannot be reversed and requires lifelong hormone replacement, while secondary causes may sometimes be treatable or reversible.

Physical Examination

A thorough physical examination provides valuable information that laboratory tests alone cannot reveal. Healthcare providers assess the size and consistency of the testicles, as smaller or softer testicles often indicate testicular dysfunction.^[9] The examination also evaluates the distribution of body and facial hair, muscle mass, and the presence of breast tissue enlargement, known as gynecomastia.^[1]

In adolescents, the physical exam helps determine whether puberty has progressed normally. Doctors look at whether the voice has deepened, whether the penis and testicles have developed appropriately, and whether growth patterns are typical for the patient’s age.^[22] Excessive growth of the arms and legs compared to the trunk, for instance, can indicate that puberty did not occur at the right time.

Additional Hormone Testing

Beyond testosterone and LH, other hormone measurements may be needed to complete the diagnostic picture. Follicle-stimulating hormone (FSH), which stimulates sperm production, is often measured alongside LH. Elevated FSH levels, like elevated LH, suggest primary testicular failure.^[3]

Doctors may also check prolactin levels, as high prolactin can interfere with testosterone production and may indicate a pituitary tumor.^[3] If a tumor is suspected, imaging studies such as an MRI of the brain may be ordered to visualize the pituitary gland.

In some cases, measuring estrogen levels can be helpful, especially in men with obesity. Fat tissue converts testosterone into estrogen, and high estrogen can suppress testosterone production, creating a vicious cycle.^[19] Identifying this imbalance can guide treatment strategies.

Genetic Testing

When primary hypogonadism is suspected in younger men or boys, or when the cause is unclear, genetic testing may be performed. Conditions like Klinefelter syndrome, where a boy is born with an extra X chromosome, are among the most common genetic causes of primary hypogonadism.^[6] A simple blood test to analyze chromosomes, known as a karyotype, can confirm this diagnosis.^[3]

Other genetic tests may be used to identify rare inherited disorders that affect testicular development or function. Genetic results not only confirm the diagnosis but also provide important information for family planning and understanding long-term health risks.

Semen Analysis

If fertility is a concern, a semen analysis is performed to evaluate sperm count and quality. Primary hypogonadism often severely affects sperm production because the same testicular cells responsible for testosterone also support sperm development.^[2] A man with primary hypogonadism may have a very low or zero sperm count, which confirms the diagnosis and helps guide discussions about fertility options.

The test involves collecting a semen sample, usually after a few days of abstinence, and analyzing it in a laboratory. Technicians assess the number of sperm, their shape, and their ability to move. Results help determine whether natural conception is possible or whether assisted reproductive techniques may be needed.^[9]

Bone Density Testing

Because testosterone plays a critical role in maintaining bone strength, men with long-standing hypogonadism are at risk for osteoporosis (loss of bone mass) and fractures. Doctors may recommend a bone density test, usually performed using a specialized X-ray technique called dual-energy X-ray absorptiometry (DEXA), to assess bone health.^[3]

This test is particularly important in older men or those who have had untreated hypogonadism for many years. Identifying low bone density allows for preventive measures, such as calcium and vitamin D supplementation, weight-bearing exercise, and sometimes medication to reduce fracture risk.

Imaging Studies

In certain situations, imaging tests provide additional diagnostic clarity. An ultrasound of the testicles can help identify structural abnormalities, tumors, or signs of past trauma or infection.^[3] If secondary hypogonadism is suspected—for example, if LH and FSH are low—an MRI or CT scan of the brain may be performed to examine the pituitary gland and hypothalamus for tumors or other abnormalities.^[9]

These imaging studies are especially important in men who also have headaches, vision changes, or unexplained breast discharge, as these symptoms can indicate a pituitary tumor that affects hormone production.

Diagnostics for Clinical Trial Qualification

Men interested in participating in clinical trials for hypogonadism treatments typically undergo a more rigorous and standardized diagnostic process. Trials have strict entry criteria to ensure that participants truly have the condition being studied and to allow for accurate measurement of treatment effects.^[13]

Most trials require documented low testosterone levels on at least two separate occasions, measured in the early morning. The specific cutoff value varies by study, but commonly used thresholds are below 300 ng/dL or below 250 ng/dL.^[15] Participants must also report symptoms consistent with hypogonadism, such as reduced libido, erectile dysfunction, fatigue, or mood disturbances. Trials generally exclude men whose low testosterone is caused by temporary factors like acute illness or recent weight loss.

Additional screening tests often include measurements of LH, FSH, and prolactin to classify the type of hypogonadism and rule out secondary causes. Blood counts, liver function tests, kidney function tests, and lipid panels are commonly performed to assess overall health and identify any conditions that could complicate treatment or interpretation of results.^[13]

Because some trials test treatments aimed at improving fertility, semen analysis is often required. Men with certain medical conditions—such as active prostate cancer, severe heart disease, or significantly elevated red blood cell counts—are typically excluded from trials due to safety concerns.^[9]

Prostate health is carefully evaluated before enrollment. This includes measurement of prostate-specific antigen (PSA), a blood test that can indicate prostate enlargement or cancer, and sometimes a digital rectal exam to physically assess the prostate.^[15] These precautions are necessary because testosterone therapy can potentially worsen pre-existing prostate conditions.

Bone density testing is sometimes included in trial protocols to assess whether investigational treatments improve bone health, a known complication of hypogonadism. Imaging studies such as MRI or ultrasound may also be performed, depending on the trial’s specific research questions.

Before enrolling, potential participants undergo informed consent, a process that ensures they fully understand the trial’s purpose, procedures, risks, and benefits. This ethical requirement protects participants and ensures they make voluntary, informed decisions about their participation.^[9]