Biomarker Deep Dive: Total Testosterone

Testosterone is one of the most searched biomarkers in health—yet it’s also one of the easiest to misinterpret. That’s because testosterone is pulsatile, circadian, highly influenced by SHBG, and often measured with assays that can vary in accuracy.

This deep dive gives you a scan-first, clinically aligned framework: how to interpret results, what to confirm next, and how to act—without jumping straight to assumptions.

TL;DR: What your testosterone result usually means

If your testosterone is low

• Don’t conclude “Low T” from a single test. Most clinical guidance recommends confirming with a repeat morning measurement, ideally with SHBG (to assess free testosterone) and gonadotropins (LH/FSH). 

• If symptoms + consistently low values are present, the next step is to identify whether this is primary (testicular) vs secondary (pituitary/hypothalamic) hypogonadism.
  
  

If your testosterone is borderline / low-normal

• This is where SHBG and free testosterone matter most. You can have “normal total” but low free (high SHBG), or low total but adequate free (low SHBG). 

• If you were sick, sleep-deprived, in a deficit, or tested late in the day: consider repeating under better conditions.

If your testosterone is “normal”

• “Normal” doesn’t automatically mean “optimal for you,” but it makes clinically significant hypogonadism less likely—especially if free T is also normal and symptoms point elsewhere. Diagnostic frameworks generally require both consistent biochemical evidence and compatible symptoms/signs. 

Educational content only—not medical advice. If you have infertility concerns, severe sexual dysfunction, gynecomastia, testicular pain/mass, or red-flag neurologic symptoms, consult a clinician.

What testosterone is

Testosterone is a steroid hormone primarily produced by the testes in men (with smaller amounts from adrenal glands; women produce lower levels from ovaries/adrenals). It supports:

• sexual function and libido

• spermatogenesis (with FSH and intratesticular testosterone)

• muscle mass and strength potential

• mood/energy (non-specific)

• bone density over time

But “testosterone” in lab reports can refer to several different things—and that’s where confusion starts.

Why testosterone results are easy to misread

1) Timing matters (a lot)

Testosterone is typically highest in the morning, and many protocols recommend drawing blood around 9am (often fasting) and repeating to confirm a low result. 

2) Total testosterone ≠ free testosterone

Most testosterone in blood is bound:

• a large fraction to SHBG (tightly bound)

• some to albumin

• only a small portion is free (bioavailable)

When SHBG is high or low, total testosterone may not reflect biologically active testosterone. That’s why guidelines frequently incorporate SHBG and free testosterone (measured or calculated) in borderline cases. 

3) Assay quality and standardization vary

Some immunoassays can be less reliable at low concentrations. Many expert bodies emphasize better standardization and the value of high-quality methods like LC–MS/MS, and programs exist to improve comparability across labs. 

Interpretation: a decision-tree that actually helps

Step 1 — Identify which marker you have

Common options:

• Total testosterone

• Free testosterone (measured by equilibrium dialysis in some settings, or calculated)

• SHBG (not testosterone, but crucial for interpreting total vs free)

If your report only includes total testosterone, that’s still usable—but often incomplete.

Step 2 — Validate the conditions of the test

Before interpreting “low” seriously, sanity-check:

• Was it drawn in the morning (roughly 7–10am)?

• Were you acutely ill, sleep-deprived, under heavy stress, or in a hard caloric deficit?

• Was this one test only?

Clinical guidance commonly emphasizes repeating the measurement to confirm. 

Step 3 — Interpret in zones (not a single magic cutoff)

Reference ranges vary by lab, assay, age, and units—so anchor your read to the lab’s interval and your context.

Zone A:

Below reference range

High likelihood this is meaningful—especially if confirmed on repeat testing and symptoms match. Next move: determine primary vs secondary drivers (LH/FSH). 

Zone B:

Borderline / low-normal

This is where you should almost always look at:

• SHBG

• free testosterone (measured or calculated)

• LH/FSH if persistent and symptomatic

  This approach appears across multiple guideline frameworks. 

Zone C: 

Mid-range normal

If symptoms exist, broaden the lens:

• thyroid, prolactin, sleep apnea risk, depression/stress, medication effects, metabolic health

• avoid tunnel vision on testosterone alone

Root causes: why testosterone runs low

Think in three buckets:

1) Functional suppression (common, often reversible)

• sleep restriction / circadian disruption

• large caloric deficit, rapid weight loss, overreaching in training

• heavy alcohol use

• acute illness

These can lower testosterone transiently, which is why repeat testing in stable conditions matters. 

2) SHBG-driven “misleading totals”

SHBG can shift with:

• thyroid status

• liver health

• age

• nutritional status

  High SHBG can make total look okay while free is low; low SHBG can make total look low while free is adequate. Guidelines explicitly account for this via SHBG/free testosterone pathways. 

3) Primary vs secondary hypogonadism (requires medical evaluation)

• Primary (testicular): testosterone low with LH/FSH high

• Secondary (pituitary/hypothalamic): testosterone low with LH/FSH low/normal

  This distinction is a cornerstone of evaluation recommendations. 

What to do next: a practical action plan

Tier 1 — Fix the measurement (1–2 weeks)

If the result is low/borderline and conditions weren’t ideal:

• repeat morning test (often fasting) when you’re well-rested and not sick

• include SHBG + albumin (to calculate free T) if available

• add LH + FSH to triage primary vs secondary pathways

  This mirrors common NHS and society-style protocols and broader guideline logic. 

Tier 2 — Address high-yield lifestyle drivers (4–8 weeks)

If you’re borderline or low-normal with symptoms, these often move the needle:

• consistent sleep schedule (and screen/light hygiene)

• resistance training with adequate recovery (avoid chronic overreaching)

• adequate calories/protein (especially if dieting aggressively)

• reduce heavy alcohol intake

• treat suspected sleep apnea (if relevant)

This tier matters because a lot of “low-ish testosterone” is contextual.

Tier 3 — Medical evaluation and targeted treatment discussion

If you have:

• persistent symptoms and

• consistently low testosterone on repeat tests under proper conditions

  …then a clinician can evaluate causes (including prolactin, thyroid, pituitary considerations, medication review, fertility goals) and discuss evidence-based management options. Major guidelines emphasize diagnosing hypogonadism only when symptoms/signs align with unequivocally and consistently low testosterone. 

Complementary biomarkers to check: the “testosterone cluster”

If testosterone is borderline/low, these are high-yield add-ons:

1. SHBG + albumin (to calculate free testosterone) 

2. LH, FSH (primary vs secondary pattern) 

3. Prolactin (especially if secondary pattern or sexual symptoms) 

4. TSH / free T4 (thyroid influences SHBG and symptoms) 

5. CBC / hematocrit (baseline and important if therapy is ever considered) 

6. Metabolic markers (HbA1c, lipids, waist/BMI context) — metabolic health strongly interacts with sex hormone patterns (not diagnostic, but useful context)

FAQ

What’s the best time to test testosterone?

Morning testing is commonly recommended (often around 9am and ideally fasting), and low results are typically confirmed with a repeat measurement. 

Should I test free testosterone or total testosterone?

Total is the usual starting point. Free testosterone becomes especially useful when SHBG is abnormal or total is borderline—many guidelines incorporate SHBG/free testosterone pathways for this reason. 

Can “normal total T” still be a problem?

Sometimes. High SHBG can reduce free testosterone even if total looks normal—so symptoms + SHBG/free T context matter. 

Are at-home tests reliable?

Accuracy depends on the specimen type, assay method, and lab quality controls. In general, testosterone measurement quality is a known issue across the field, and standardization programs exist to improve comparability. 

Is testosterone therapy the obvious fix for low values?

Not automatically. Multiple guidelines stress confirming persistent biochemical low testosterone plus compatible symptoms/signs and evaluating underlying causes first. 

References

• Endocrine Society — Testosterone Therapy in Men With Hypogonadism (Clinical Practice Guideline, 2018): https://www.endocrine.org/clinical-practice-guidelines/testosterone-therapy 

• American Urological Association — Testosterone Deficiency Guideline: https://www.auanet.org/guidelines-and-quality/guidelines/testosterone-deficiency-guideline 

• AUA Guideline PDF (Evaluation and Management of Testosterone Deficiency): https://www.auanet.org/documents/Guidelines/PDF/Testosterone-Deficiency-JU.pdf 

• NHS protocol example (morning repeat testosterone + SHBG/LH/FSH): https://www.nnuh.nhs.uk/publication/download/adult-testosterone-replacement-and-monitoring-jcg0043-v4/ 

• Centers for Disease Control and Prevention — Steroid Hormones Standardization Programs (testosterone standardization): https://www.cdc.gov/clinical-standardization-programs/php/hormones/index.html 

• CDC HoSt Certified Total Testosterone Procedures (PDF): https://www.cdc.gov/clinical-standardization-programs/media/pdfs/2024/04/CDC-Certified-Testosterone-Procedures-508.pdf