Low Testosterone: Symptoms, Causes, and When to Get Tested

Short answer: low testosterone (male hypogonadism) is a clinical syndrome — symptoms plus repeatedly low morning labs — not a single number or a vague sense of being run down. Guidelines support testing when symptoms fit the pattern, not routine screening of asymptomatic men.

"Low T" gets thrown around a lot, but clinically it's a specific diagnosis — not just a number on a lab report and not just a feeling of being run down. Here's what actually defines low testosterone, the documented symptoms and causes, and when the evidence says it's worth getting tested.

What Counts as a Diagnosis

Male hypogonadism is a clinical syndrome — it's defined by the combination of low testosterone levels and a matching set of symptoms, not by a lab value on its own.^[1]

Documented Symptoms

The symptom list associated with hypogonadism is broader than most people expect. It includes reduced libido, erectile dysfunction and loss of spontaneous erections, lowered sperm count and infertility, breast enlargement or tenderness, reduced energy, reduced muscle mass, shrinkage of the testes, irritability, difficulty concentrating, depressed mood, and — in cases of very low testosterone — hot flashes.^[3] Left untreated over time, low testosterone can also contribute to loss of body hair, further muscle loss, weakened bones, low red blood cell counts, and smaller testes.^[3]

• Reduced sex drive and erectile dysfunction
• Lowered sperm count or infertility
• Reduced energy and muscle mass
• Breast enlargement or tenderness
• Irritability, trouble concentrating, low mood
• Testicular shrinkage

Where Low Testosterone Comes From

Hypogonadism is classified by where the underlying problem starts. Primary hypogonadism comes from a defect in the testes themselves — it shows up as low testosterone alongside impaired sperm production and elevated LH/FSH (the pituitary hormones that signal the testes to produce testosterone). Secondary hypogonadism comes from a problem in the hypothalamus or pituitary gland instead, producing low testosterone with low or inappropriately normal LH/FSH.^[3]

The most common genetic cause of primary hypogonadism is Klinefelter syndrome, a chromosomal condition (47,XXY) that impairs the sperm-producing tissue in the testes.^[3] Acquired causes of primary hypogonadism include chemotherapy or radiation, testicular infection such as mumps, physical trauma, and high doses of certain anti-androgen medications.^[3] Secondary hypogonadism is more often linked to pituitary tumors or disease, elevated prolactin, iron overload, and certain medications, including opioids and corticosteroids.^[3]

There's also a "mixed" category — part primary, part secondary — specifically associated with aging, alcohol use disorder, chronic conditions like kidney or liver failure or severe HIV infection, and medications like corticosteroids.^[3] More broadly, low testosterone shows up alongside obesity, sleep disorders, and type 2 diabetes often enough that these are considered meaningful associations in their own right.^[3]

How Much Does Testosterone Really Decline With Age?

The Massachusetts Male Aging Study, a large population-based cohort of men aged 40–70, is one of the most cited sources on this question. It found total serum testosterone declines by roughly 0.4% to 1.6% per year depending on the measurement approach used, while free testosterone — the biologically active portion — declines faster, at around 1.2% to 2.8% per year.^[5]

Age isn't the whole story, though. The same research program found men with pre-existing chronic health conditions had testosterone levels running 10–15% lower across every age group studied compared to healthier men of the same age — meaning overall health status matters independently of how old you are.^[4]

How the Diagnosis Actually Gets Made

Professional societies don't fully agree on where to draw the line. The Endocrine Society's clinical practice guideline uses 264 ng/dL as its lower-limit threshold for total testosterone, derived from the 2.5th percentile of a harmonized reference range in healthy, nonobese men aged 19–39 — while other societies use higher cutoffs, generally in the 300–350 ng/dL range.^[8] The full harmonized reference range for that same healthy young-adult population runs from 264 to 916 ng/dL.^[8]

Regardless of the exact cutoff used, the diagnostic process itself is fairly standardized. The Endocrine Society is explicit that a diagnosis requires both consistent symptoms and unequivocally, repeatedly low testosterone — a single low lab value isn't enough.^[8] The recommended approach is to measure fasting, morning total testosterone first (since levels follow a daily rhythm and peak in the morning), then confirm with a second morning fasting test on a separate day before concluding testosterone is actually low.^[8] In men with borderline results or where sex hormone-binding globulin may be off, guidelines also recommend measuring free testosterone directly for a more accurate picture.^[8] Once low testosterone is confirmed, LH and FSH are typically measured to figure out whether the cause is primary (testicular) or secondary (hypothalamic-pituitary).^[8]

When It's Actually Worth Getting Tested

Testing makes sense when a man has symptoms that fit the pattern above — not as routine screening for men who feel fine. The Endocrine Society states plainly that there isn't sufficient evidence to support screening asymptomatic men for low testosterone.^[2]If you're noticing several of the symptoms above consistently, that's the signal to get tested — not a single off day or one unusual lab result.

If testing does confirm low testosterone, the next step is usually a conversation about whether treatment makes sense for your specific situation — see what TRT is actually proven to help with, then compare how different telehealth providers approach labs and monitoring on RENVA's Men's Health / TRT hub.

Frequently Asked Questions