Nelson Vergel
Founder, ExcelMale.com
Send one blood sample from a hypogonadal man to 1,133 labs and the reported testosterone ranges from 45 to 365 ng/dL. That happened in a College of American Pathologists proficiency survey (Matsumoto, 2022). The same man could be told he is severely deficient or completely normal depending on which lab ran his blood.
Getting this right matters before anyone writes a prescription. In studies reviewed by Matsumoto, only 10 to 40% of men starting testosterone had the two measurements guidelines require, and 12 to 46% had no testosterone level checked at all in the year before treatment. This comes up constantly on ExcelMale: a new member posts a single afternoon lab result and a prescription, and nobody ever checked LH, FSH, or SHBG.
Which Symptoms Should Prompt a Testosterone Test?
Sexual symptoms are the strongest reason to test: low libido, fewer morning erections, and erectile dysfunction. In the European Male Ageing Study of 3,369 men aged 40 to 79, these three sexual symptoms were the ones that tracked with low testosterone, while fatigue and low mood showed weaker links (Wu et al., 2010).
Physical and psychological symptoms count, but they overlap with depression, poor sleep, obesity, and many medications. Fatigue alone is a weak reason to start a hormone workup. A good clinician looks for other causes first, because many of them can be fixed without testosterone.
Which Signs Are Most Specific to Low Testosterone?
Loss of body hair, very small testes, and incomplete sexual development are the most specific signs, and they usually mean severe, long-standing deficiency (Matsumoto, 2022). Normal adult testis volume is 15 to 30 mL. Testes under 6 mL raise suspicion for Klinefelter syndrome, the most common genetic cause of primary hypogonadism.
What Can Falsely Lower a Testosterone Result?
Afternoon blood draws, eating before the test, acute illness, and certain drugs can all push a result below the reference range in a man whose testes and pituitary work normally. Testosterone peaks in the morning. More than half of men over 65 with a low afternoon level test normal in the morning (Matsumoto, 2022).
Food matters as well. The 2026 European Association of Urology (EAU) guidelines report that a non-fasting sample can underestimate total testosterone by more than 30%. Acute illness, surgery, opioids, glucocorticoids, and the energy deficit of crash dieting or overtraining suppress the axis temporarily, and the Endocrine Society advises waiting until these resolve before testing (Bhasin et al., 2018).
Why Does One Low Result Not Prove Hypogonadism?
Testosterone varies so much from day to day that 30 to 35% of men with one low result test normal on repeat (Matsumoto, 2022). In one cohort of men with a single value under 250 ng/dL, 20% averaged above 300 ng/dL over the next six months. None of the men with two low readings did. Every major guideline requires two morning, fasting samples on separate days for this reason.
Why Do Two Labs Give Different Testosterone Numbers?
Most labs use automated immunoassays that are not standardized, so the same blood produces different values and each lab sets its own reference range. Across 120 US labs, the lower limit of normal for total testosterone ranged from 160 to 300 ng/dL (Matsumoto, 2022). UK labs ranged from 4.9 to 11 nmol/L, roughly 141 to 317 ng/dL (Livingston and Heald, 2023).
Mass spectrometry is more specific, but it is no guarantee of accuracy. UK external quality data show some of the better immunoassays outperforming some mass spectrometry platforms (Livingston and Heald, 2023). What matters most is whether the assay is calibrated to a reference standard.
What Is a CDC-Certified Testosterone Assay?
A CDC-certified assay is one that passed the Centers for Disease Control and Prevention Hormone Standardization Program, which checks results against a reference method. Certified assays can use the harmonized reference range of 264 to 916 ng/dL, which Travison and colleagues derived from 9,054 men and applied to healthy, non-obese men under 40 (Travison et al., 2017). Most large US reference labs offer a certified test, but some also sell non-certified versions, so ask which one you are getting. The ExcelMale thread on harmonized reference ranges for total and free testosterone covers the details.
What Testosterone Level Confirms Hypogonadism?
No single cutoff is universal: major guidelines place it between roughly 230 and 350 ng/dL (8 to 12 nmol/L), with a gray zone in between. The table compares the main positions.
| Guideline | Total testosterone cutoff | Free testosterone guidance |
|---|---|---|
| Endocrine Society (2018) | Below 264 ng/dL (9.2 nmol/L) on a CDC-certified assay | Measure when total T is near the lower limit or SHBG is abnormal |
| AUA (2018) | Below 300 ng/dL (10.4 nmol/L) | Consider in selected men, such as those with altered SHBG |
| EAU (2026) | 12 nmol/L (about 350 ng/dL) or lower in symptomatic men | Calculated free T when SHBG is altered; about 220 pmol/L suggested, evidence limited |
| SfE/ACB, UK (2023) | Below 8 nmol/L (about 230 ng/dL) likely; 8 to 12 gray zone; above 12 unlikely | Calculated free T when SHBG is outside the reference range |
Under the UK Society for Endocrinology and Association for Clinical Biochemistry statement, a single result above 12 nmol/L (about 350 ng/dL) makes hypogonadism unlikely, even if another reading is lower (Livingston and Heald, 2023). The ExcelMale summary of the 2026 EAU testosterone measurement recommendations walks through the European position.
Our view: the cutoff matters less than whether the test was done correctly and whether symptoms fit. A man at 320 ng/dL with high SHBG and low free testosterone can be more deficient than a man at 260 ng/dL with low SHBG and normal free testosterone.
When Do You Need Free Testosterone, and Which Method Is Accurate?
You need free testosterone when total testosterone falls between about 200 and 400 ng/dL, or when you have a condition that shifts SHBG, such as obesity, aging, liver disease, thyroid disease, or HIV (Matsumoto, 2022). Free testosterone is the 2 to 4% of circulating testosterone not bound to proteins, the fraction that enters tissues and acts on androgen receptors.
Total testosterone misleads in both directions. In 3,672 US veterans, 61.7% of men with low total testosterone had normal calculated free testosterone (Matsumoto, 2022). Obesity lowers SHBG, which drags total T down while free T stays normal. Aging raises SHBG, which can hide a real deficiency behind a normal total. Below about 150 ng/dL total, free testosterone adds little, because the chance it is normal is very low.
Why Should You Avoid Direct Free Testosterone Tests?
Direct (analog) immunoassays for free testosterone are inaccurate, reading about ten times lower than equilibrium dialysis, and the Endocrine Society advises against them (Bhasin et al., 2018). Ask for free testosterone by equilibrium dialysis, or order total T, SHBG, and albumin and calculate it. ExcelMale hosts a free testosterone calculator for this. Calculated values carry the error of all three assays, a limitation discussed in the thread on whether calculated free testosterone still holds up.
How Do LH and FSH Separate Primary From Secondary Hypogonadism?
Low testosterone with high LH and FSH means the testes are failing (primary hypogonadism), while low testosterone with low or normal LH and FSH means the pituitary or hypothalamus is not sending the signal (secondary hypogonadism). LH and FSH should be drawn in the same sample as the repeat testosterone test. In healthy fertile young men, LH runs 1.6 to 8.0 IU/L and FSH runs 1.3 to 8.4 IU/L (Matsumoto, 2022).
| Feature | Primary hypogonadism | Secondary hypogonadism |
|---|---|---|
| Where the problem is | Testes | Pituitary or hypothalamus |
| LH and FSH | High, with FSH often higher than LH | Low or inappropriately normal |
| Common causes | Klinefelter syndrome, mumps orchitis, testicular injury or surgery, chemotherapy, advanced age | Obesity, opioids, anabolic steroids, glucocorticoids, high prolactin, pituitary tumors, hemochromatosis |
| Fertility with hormone therapy | Rarely restored; assisted reproduction usually needed | Often restored with hCG, FSH, or GnRH |
| Next tests | Karyotype if testes are under 6 mL | Prolactin, iron saturation, MRI when indicated |
Compensated hypogonadism is normal testosterone with elevated LH, meaning the testes need extra stimulation to keep up. It resembles subclinical hypothyroidism, and whether it needs treatment is unsettled. High-dose biotin supplements can interfere with LH and FSH immunoassays, so stop biotin for a few days before testing.
Which Follow-Up Tests Find the Cause?
Secondary hypogonadism calls for prolactin and iron saturation, while primary hypogonadism with very small testes calls for a karyotype (Matsumoto, 2022). The full list depends on what the first results show:
- Prolactin, to rule out a prolactin-secreting pituitary tumor or a medication effect.
- Transferrin (iron) saturation, to screen for hemochromatosis, which suppresses the pituitary.
- Pituitary MRI when total T is below about 150 ng/dL with low LH and FSH, prolactin stays high after stopping drugs that raise it, other pituitary hormones are low, or there are new headaches or vision changes.
- Free T4 and morning cortisol when broader pituitary failure is suspected.
- Karyotype when primary hypogonadism comes with testes under 6 mL.
- Semen analysis on at least two occasions, 1 to 2 weeks apart, if fertility matters.
- Bone density scan in older men, especially over 70.
Do the fertility workup before any testosterone starts. TRT suppresses sperm production and erases the hormone pattern needed for a diagnosis.
Is Your Hypogonadism Functional or Organic, and Why Does It Change Treatment?
Organic hypogonadism is caused by permanent damage or a congenital defect in the testes, pituitary, or hypothalamus. Functional hypogonadism is caused by reversible suppression from obesity, type 2 diabetes, medications, or illness, with no structural disease of the axis (de Silva et al., 2024). Functional cases are far more common, and most age-related low testosterone in middle-aged men falls into this group (Matsumoto, 2022).
| Feature | Organic hypogonadism | Functional hypogonadism |
|---|---|---|
| Cause | Irreversible structural, genetic, or destructive disease | Obesity, diabetes, opioids, glucocorticoids, illness, energy deficit |
| Testosterone | Consistently low, often severely | Mildly low, often near the cutoff |
| LH and FSH | Clearly high (primary) or clearly low (secondary) | Normal to low-normal |
| First-line approach | Testosterone, or gonadotropins if fertility is the goal | Treat the cause first; testosterone if symptoms persist |
De Silva and colleagues call health optimization the gold-standard strategy for functional hypogonadism, while noting that testosterone gives modest sexual-function benefits without raising short- to medium-term cardiovascular or prostate cancer risk (de Silva et al., 2024). The EAU estimates that diet and exercise raise testosterone by about 1 to 2 nmol/L (roughly 30 to 60 ng/dL) in overweight men.
In practice the line blurs. A 52-year-old with a BMI of 34, sleep apnea, and a total T of 240 ng/dL has functional hypogonadism on paper. If weight loss stalls and his symptoms persist, many clinicians will treat him, and ExcelMale members debate this exact case often. The thread on functional hypogonadism and modern testosterone therapy lays out both sides.
How Long Must You Stop TRT Before Retesting?
Stop gels, orals, and buccal testosterone for 2 to 4 weeks, cypionate or enanthate injections for 2 to 3 months, and undecanoate injections or pellets for 6 to 12 months before measuring testosterone and gonadotropins (Matsumoto, 2022). Even then, older men and men who used high doses for years may stay suppressed. A low LH after stopping TRT does not prove you had secondary hypogonadism before you started, which is the main reason to get a full baseline panel first.
Frequently Asked Questions
What Time of Day Should Testosterone Be Tested?
Between 7 and 10 a.m., after an overnight fast. UK guidance accepts samples drawn before 11 a.m. Night-shift workers may need individual timing because their rhythm is shifted.
Is 300 ng/dL Considered Low Testosterone?
It is the AUA cutoff, so 300 ng/dL sits on the border. Whether it means hypogonadism depends on symptoms, SHBG, free testosterone, and the assay used.
Can You Have Normal Total Testosterone and Still Be Hypogonadal?
Yes. High SHBG can leave free testosterone low despite a normal total, which is common in older men. Free testosterone by equilibrium dialysis or calculation reveals it.
Do I Need an MRI for Low Testosterone?
Only in specific cases: total T below about 150 ng/dL with low LH and FSH, persistently high prolactin, other pituitary hormone deficits, or new headaches and vision changes. Most men with mild secondary hypogonadism do not need one.
Should LH and FSH Be Tested Before Starting TRT?
Yes, always. Testosterone therapy suppresses both hormones within weeks, so testing afterward cannot tell you whether the original problem was in the testes or the pituitary.
Related ExcelMale Forum Discussions
- Adult Male Hypogonadism: Diagnosis and Management: Livingston and Heald’s laboratory review of assay variation and the UK SfE/ACB testosterone thresholds.
- Approach to the Diagnosis and Evaluation of Hypogonadism: Matsumoto’s step-by-step diagnostic framework, including free T indications and TRT washout times.
- Male Hypogonadism: Pathogenesis, Diagnosis, and Management: The 2024 Lancet Diabetes & Endocrinology review comparing organic and functional hypogonadism.
- Summary of the EAU Guidelines on Measurement of Total T: The 2026 European thresholds and preanalytical rules for testosterone testing.
- Calculated Free Testosterone Revisited: When calculated free testosterone helps the diagnosis and where it falls short.
Key References
1. Bhasin S, Brito JP, Cunningham GR, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2018. https://doi.org/10.1210/jc.2018-00229
2. Matsumoto AM. Diagnosis and Evaluation of Hypogonadism. Endocrinol Metab Clin North Am. 2022. Redirecting
3. Livingston M, Heald AH. Adult Male Hypogonadism: A Laboratory Medicine Perspective on Its Diagnosis and Management. Diagnostics. 2023. https://doi.org/10.3390/diagnostics13243650
4. de Silva NL, Papanikolaou N, Grossmann M, et al. Male hypogonadism: pathogenesis, diagnosis, and management. Lancet Diabetes Endocrinol. 2024. Redirecting
5. Travison TG, Vesper HW, Orwoll E, et al. Harmonized Reference Ranges for Circulating Testosterone Levels in Men of Four Cohort Studies in the United States and Europe. J Clin Endocrinol Metab. 2017. https://doi.org/10.1210/jc.2016-2935
6. Wu FCW, Tajar A, Beynon JM, et al. Identification of Late-Onset Hypogonadism in Middle-Aged and Elderly Men. N Engl J Med. 2010. https://doi.org/10.1056/NEJMoa0911101
7. Mulhall JP, Trost LW, Brannigan RE, et al. Evaluation and Management of Testosterone Deficiency: AUA Guideline. J Urol. 2018. https://doi.org/10.1016/j.juro.2018.03.115
8. Jayasena CN, Anderson RA, Llahana S, et al. Society for Endocrinology guidelines for testosterone replacement therapy in male hypogonadism. Clin Endocrinol (Oxf). 2022. https://doi.org/10.1111/cen.14633
Conclusion
Your baseline numbers keep paying off long after the diagnosis. SHBG in particular shapes how you will feel on treatment: men with low SHBG clear free testosterone faster and often do better on smaller, more frequent injections, a pattern ExcelMale members report again and again. Get the full panel once, done properly, and keep a copy. When you are ready to weigh options, start with the thread on male hypogonadism treatment choices and browse the ExcelMale testosterone and men’s health articles library.
By Nelson Vergel | B.S. Chemical Engineering, MBA | Founder, ExcelMale.com | 34+ years on TRT | NIH and FDA advisory panel service | Author: Testosterone: A Man’s Guide, Beyond Testosterone, The hCG Advantage, and From Pills to Implants. Updated October 2026.
About ExcelMale: ExcelMale.com is a men’s health community founded by Nelson Vergel, with more than 24,000 members and over 20 years of archives covering testosterone replacement, hormone optimization, fertility, and men’s sexual health.
