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FREE_TESTOSTERONEvsTestosterone

Free Testosterone vs Total Testosterone

Understanding the difference between bioavailable free testosterone and total testosterone, and why both are important for assessing hormonal health.

Aspect
FREE_TESTOSTERONE
Testosterone
What it measures
The unbound, bioavailable testosterone that can enter cells and have biological effects
All testosterone in the blood - includes free, SHBG-bound, and albumin-bound
Percentage of total
Only 1-3% of total testosterone
100% - the complete picture including bound testosterone
Clinical relevance
More directly related to symptoms - represents what's actually available to tissues
Standard screening test - gives overall production level
When discrepancy occurs
Can be low even with normal total T if SHBG is high
Can be normal while free T is low due to binding proteins
Factors affecting each
SHBG levels, obesity, insulin resistance, thyroid function
Testicular function, pituitary function, age

Key Differences

  • •Free testosterone is the biologically active form; total includes inactive bound forms
  • •You can have symptoms with normal total T but low free T
  • •SHBG levels significantly affect free testosterone but not total
  • •Free T correlates better with symptoms in some patients
  • •Measuring both gives a more complete picture of hormonal status

Why Both Matter

Understanding both free and total testosterone is crucial for accurately assessing hormonal health. Total testosterone measures all testosterone in your blood, but the majority (97-99%) is bound to proteins - primarily sex hormone-binding globulin (SHBG) and albumin. Only free testosterone, the unbound fraction, can enter cells and produce biological effects.

This distinction matters clinically because some men have normal total testosterone but low free testosterone due to elevated SHBG. These individuals often experience classic low-T symptoms despite "normal" total testosterone levels. Conditions that increase SHBG include aging, hyperthyroidism, liver disease, and certain medications.

Conversely, conditions like obesity, insulin resistance, and hypothyroidism can lower SHBG, resulting in higher free testosterone relative to total. This is why men with obesity may have low total testosterone but fewer symptoms than expected.

For accurate hormone assessment, especially in men with symptoms or borderline total testosterone, measuring both free and total testosterone, along with SHBG, provides the complete picture needed for proper diagnosis and treatment decisions.

Learn more about

FREE_TESTOSTERONE

Learn more about

Testosterone

The primary male sex hormone also present in females.

Frequently Asked Questions

Why is my total testosterone normal but I have low-T symptoms?
This often occurs when SHBG is elevated, binding more testosterone and leaving less free testosterone available. Check your free testosterone and SHBG levels for a complete picture.
Which test is better for diagnosing low testosterone?
Both are valuable. Total testosterone is the standard screening test, but free testosterone may better correlate with symptoms in some patients. Testing both, along with SHBG, provides the most accurate assessment.
Can I calculate free testosterone from other values?
Yes, free testosterone can be calculated using total testosterone, SHBG, and albumin levels. While not as accurate as direct measurement, calculated free testosterone is clinically useful and often used.
What causes high SHBG that lowers free testosterone?
Aging, hyperthyroidism, liver disease, HIV, certain medications, and low body weight can increase SHBG. Estrogen use also significantly increases SHBG. Addressing underlying causes may help.

Track Both Markers Over Time

Upload your blood test results to BloodTrack and monitor both FREE_TESTOSTERONE and Testosterone. See how they change together over time.

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