Which blood tests for low testosterone
Both US guidelines agree on the core: diagnose low testosterone only in a man with symptoms, from two early-morning total testosterone tests on separate days. The AUA guideline (2018, validity confirmed 2024) uses 300 ng/dL as a reasonable cut-off, then asks for LH in every low result, prolactin when LH is low or normal, and hemoglobin, hematocrit and PSA (men over 40) before any treatment. The Endocrine Society guideline adds free testosterone when total testosterone is borderline or SHBG is likely to be abnormal.
| Marker | Why it matters | What a result suggests | On SiPhox |
|---|---|---|---|
| Total testosterone | The first test, taken early in the morning | Under 300 ng/dL twice, with symptoms, meets the AUA definition | Longevity (men), Hormone Focus, Ultimate 360, GLP (men) |
| SHBG | Controls how much testosterone is free | Low SHBG (obesity, insulin resistance) lowers total T without always lowering free T | Longevity (men), Thyroid Focus, Hormone Focus, Ultimate 360, GLP |
| Free testosterone | The fraction tissues can use | Low free T confirms deficiency when total T is borderline | Longevity (men), Hormone Focus, Ultimate 360, GLP |
| LH and FSH | Tell testicular (primary) from pituitary (secondary) causes | High LH with low T is primary; low or normal LH is secondary | Hormone Focus, Ultimate 360 |
| Prolactin | High prolactin suppresses testosterone | Raised with low or normal LH needs a pituitary workup | Hormone Focus, Ultimate 360 |
| Estradiol | AUA: measure if there are breast symptoms | High estradiol with breast growth needs a doctor | Hormone Focus, Ultimate 360, GLP |
| Hematocrit and hemoglobin | Baseline before any therapy; low T can cause mild anemia | Needed so later rises on treatment can be judged | Longevity, Heart & Metabolic, Ultimate 360, GLP |
| PSA | Baseline before therapy in men over 40 (AUA) | A raised PSA is checked before treatment starts | Hormone Focus (men), Ultimate 360 (men) |
| Iron saturation, ferritin | Iron overload is one cause of secondary hypogonadism | High saturation needs a doctor | Ultimate 360, GLP |
| HbA1c | Diabetes and obesity are linked to low testosterone | 5.7% to 6.4% is prediabetes, 6.5% or more diabetes range | Longevity, Heart & Metabolic, Ultimate 360, GLP |
Symptoms that justify a low testosterone test
The Endocrine Society recommends testing men with symptoms, not screening everyone. The more specific signs are lower sex drive, fewer morning erections, erectile dysfunction, breast tenderness or enlargement, loss of body hair, small or shrinking testes, and low bone density or a low-trauma fracture. Less specific ones include low energy, low mood, poor concentration, reduced strength and more body fat. The AUA adds that men with unexplained anemia, low bone density, diabetes, or long-term opioid or steroid use may warrant testing even with fewer symptoms.
If you have none of these and just want a number, a general panel that includes testosterone alongside heart and metabolic markers is better value than a hormone-only test; see our at-home blood test for men guide.
What counts as low testosterone
Sources: Travison et al., J Clin Endocrinol Metab 2017 (healthy non-obese men aged 19 to 39, CDC-standardized assays); AUA testosterone deficiency guideline.
The Endocrine Society guideline uses the harmonized range from Travison 2017, measured with CDC-standardized assays: 264 to 916 ng/dL in healthy, non-obese men aged 19 to 39, with a median of 531 ng/dL. The AUA uses under 300 ng/dL. Both are cut-offs for men with symptoms; a low number with no symptoms is not a diagnosis. Lab ranges differ, especially between labs that do and do not use standardized assays, so compare against the range printed on your report. To convert, ng/dL x 0.0347 = nmol/L.
Finding the cause of low testosterone
Once two morning results are low, the next blood tests sort men into two groups:
- Primary hypogonadism (testes): low testosterone with high LH and FSH. Causes include Klinefelter syndrome, past mumps, chemotherapy or injury.
- Secondary hypogonadism (pituitary or hypothalamus): low testosterone with low or normal LH. This is the more common pattern in adult men and is often functional, driven by obesity, diabetes, opioids, sleep apnea or illness. It also includes high prolactin and iron overload, which is why prolactin and iron saturation are checked.
The distinction matters because functional causes can improve without testosterone, and because testosterone therapy suppresses sperm production, a key issue for men who want children. Our TRT blood test guide covers monitoring if you do start treatment.
Worked example: 44, tired, borderline result
Illustrative numbers. A 44-year-old man with a BMI of 32 and low libido tests twice, two weeks apart, at 8 a.m.:
| Marker | Test 1 | Test 2 |
|---|---|---|
| Total testosterone | 285 ng/dL | 312 ng/dL |
| SHBG | 17 nmol/L | 18 nmol/L |
| Free testosterone (calculated) | Within the lab range | Within the lab range |
| LH | Normal | Not repeated |
| HbA1c | 6.0% | Not repeated |
One of two results is under 300 ng/dL, but SHBG is low, as it often is with excess weight and insulin resistance, and free testosterone is normal. That is the case the Endocrine Society had in mind when it recommended free testosterone for borderline results. His HbA1c of 6.0% is in the prediabetes range. The likely conversation with his doctor is about weight, blood sugar and sleep first, then a repeat. Weight loss and better glucose control tend to raise SHBG and testosterone.
What skews a testosterone result
- Time of day: testosterone peaks in the morning. Both guidelines base their cut-offs on early-morning draws.
- Acute illness, surgery, crash dieting or overtraining in the days before.
- Medicines: opioids and glucocorticoids lower testosterone, per the Endocrine Society.
- Poor sleep or night shifts.
- Biotin: the FDA warns it can interfere with hormone immunoassays.
For the practical steps of a home draw, read our at-home testosterone test guide. For normal values by decade, see testosterone levels by age.
What an at-home test can and cannot do for low T
- Give two morning measurements of total T, free T and SHBG without a lab trip
- Add LH, FSH, prolactin, estradiol and PSA in the same draw
- Build a record to take to a doctor
- Diagnose hypogonadism: a diagnosis needs a clinician and your symptoms
- Check fertility (semen analysis) or image the pituitary
- Prescribe or dose testosterone
Best-fit SiPhox panel for a low testosterone workup
| If you want | Test | Choose |
|---|---|---|
| The diagnostic hormone set | Total T, free T, SHBG, LH, FSH, prolactin, estradiol, PSA | Hormone Focus |
| Testosterone plus metabolic and blood markers | Total T, free T, SHBG, hemoglobin, hematocrit, HbA1c, ApoB | Longevity Essentials |
| Everything, including iron saturation | All of the above plus iron studies, thyroid, B12 | Ultimate 360 |
| A confirming venous test before treatment | Two morning venous total T | Your doctor |
A sensible plan is Hormone Focus for the first morning test and Longevity Essentials for the second, which repeats total T, free T and SHBG and adds hemoglobin, hematocrit and HbA1c. Two tests cost $298 with shipping, or $273 if the $99 first-test price applies. Ultimate 360 covers both halves in one draw for $274.
Hormone Focus
Sex hormones for men and women, including PSA for men and progesterone for women.
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Longevity Essentials
The default panel: heart, metabolic, hormone and inflammation markers in one draw.
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Ultimate 360
Everything on the four core panels plus iron studies, B12 and folate, GGT and PSA.
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Frequently asked questions
What testosterone level is considered low?
The AUA uses under 300 ng/dL on two early-morning tests, in a man with symptoms. The Endocrine Society uses the harmonized lower limit of 264 ng/dL. Lab ranges vary.
What time should a testosterone blood test be done?
Early morning, roughly 7 to 10 a.m., ideally fasting and after normal sleep. Guideline cut-offs are based on morning values.
Why test LH and FSH with testosterone?
They show where the problem starts. High LH with low testosterone points to the testes; low or normal LH points to the pituitary or hypothalamus, which leads to prolactin and iron tests.
Do I need free testosterone?
When total testosterone is near the cut-off or SHBG is likely abnormal, for example with obesity, diabetes, older age or thyroid disease. Free testosterone can be normal when total is low.
Can low testosterone be diagnosed with one test?
No. Both the AUA and Endocrine Society require two separate early-morning measurements, plus symptoms.
Sources
- American Urological Association: Evaluation and management of testosterone deficiency (2018, validity confirmed 2024)
- Bhasin S et al. Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab 2018
- Endocrine Society: Testosterone therapy guideline, full text and recommendations
- Travison TG et al. Harmonized reference ranges for circulating testosterone levels in men. J Clin Endocrinol Metab 2017
- MedlinePlus: Testosterone levels test
- MedlinePlus: Luteinizing hormone (LH) levels test
- MedlinePlus: Prostate-specific antigen (PSA) test
- NIDDK (NIH): Diabetes tests and diagnosis
- FDA: Biotin interference with lab tests
- SiPhox Health: Hormone Focus panel (checked 29 Sep 2026)
- SiPhox Health: Longevity Essentials panel and add-ons (checked 29 Sep 2026)
- SiPhox Health: Ultimate 360 panel (checked 29 Sep 2026)