Free Testosterone
Calculate free and bioavailable testosterone using the Vermeulen method for androgen assessment.
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Calculated free and bioavailable testosterone using the Vermeulen method for androgen assessment
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Why: Understanding free testosterone helps you make better, data-driven decisions.
How: Enter Total Testosterone, Unit, SHBG to calculate results.
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✅ Normal Young Male
Healthy 30-year-old with normal levels
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🔴 Primary Hypogonadism
Low testosterone with elevated LH
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⚠️ Secondary Hypogonadism
Low testosterone with low/normal LH
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📊 High SHBG
Normal total T but low free T due to high SHBG
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📉 Low SHBG (Obesity)
Low SHBG with higher free T percentage
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💉 On TRT
Patient on testosterone replacement
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❓ Borderline Low
Gray zone testosterone with symptoms
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Sample Scenarios
✅ Normal Young Male
Healthy 30-year-old with normal levels
🔴 Primary Hypogonadism
Low testosterone with elevated LH
⚠️ Secondary Hypogonadism
Low testosterone with low/normal LH
📊 High SHBG
Normal total T but low free T due to high SHBG
📉 Low SHBG (Obesity)
Low SHBG with higher free T percentage
💉 On TRT
Patient on testosterone replacement
❓ Borderline Low
Gray zone testosterone with symptoms
🔬 Core Lab Values
👤 Patient Information
📋 Symptoms
🧪 Additional Labs (Optional)
🏥 Medical History
Testosterone Results
Low Testosterone - Evaluation Recommended
Total T
Normal
Free T
Severely Low
Bioavailable T
Severely Low
Free %
Normal 1-3%
Percentile
for age
Detailed Analysis
| Free Testosterone | 1.82 ng/dL (Severely Low) |
| Bioavailable Testosterone | 0.9 ng/dL (Severely Low) |
| SHBG Interpretation | Normal SHBG |
| Age-Expected Range | 201 - 797 ng/dL |
| Hypogonadism Likelihood | Possible - LH/FSH needed for classification |
| Hypogonadism Type | Not applicable |
| Symptom Correlation | No significant hypogonadal symptoms reported |
Testosterone Binding Distribution
📊 Visual Analysis
Binding Distribution
Age-Related Decline
📋 Recommendations
Low testosterone confirmed - clinical evaluation warranted
🧪 Additional Testing
LH and FSH to differentiate primary vs secondary hypogonadism
Repeat morning testosterone (before 10 AM) to confirm
Prolactin level
Complete metabolic panel
🌿 Lifestyle Interventions
Regular resistance exercise can boost testosterone
Optimize sleep (7-9 hours) - sleep deprivation lowers T
Minimize alcohol consumption
Ensure adequate vitamin D and zinc intake
Manage stress - chronic stress elevates cortisol, lowers T
👨⚕️ Referrals
Endocrinology consultation recommended
Clinical Note: Calculated free testosterone using the Vermeulen method is an estimate. Equilibrium dialysis remains the gold standard for free T measurement. Results should be interpreted in clinical context. Two low morning testosterone measurements are required to diagnose hypogonadism.
For informational purposes only — not medical advice. Consult a healthcare professional before acting on results.
Understanding Testosterone Measurements
Testosterone circulates in three forms: tightly bound to SHBG (~44%), loosely bound to albumin (~54%), and unbound/free (~2%). Only free testosterone and albumin-bound testosterone are biologically active.
Total Testosterone
- • All circulating testosterone
- • Standard screening test
- • May be misleading if SHBG abnormal
- • Normal: 264-916 ng/dL (young men)
Free Testosterone
- • Unbound, immediately active
- • ~1-3% of total
- • Best measure of active hormone
- • Measured or calculated
Bioavailable Testosterone
- • Free + albumin-bound
- • ~50-60% of total
- • Available for tissue uptake
- • Better correlates with symptoms
When to Check Free Testosterone
Check Free T When:
- • Total T is borderline (200-400 ng/dL)
- • SHBG is abnormal
- • Symptoms despite normal total T
- • Obesity or metabolic syndrome
- • Liver disease, hyperthyroidism
- • Aging (SHBG increases with age)
Factors Affecting SHBG:
- • Aging
- • Liver disease
- • Hyperthyroidism
- • Anticonvulsants
- • HIV infection
- • Obesity
- • Hypothyroidism
- • Nephrotic syndrome
- • Androgens/steroids
- • Insulin resistance
Hypogonadism Classification
Primary Hypogonadism
Low T + High LH/FSH (testicular failure)
- • Klinefelter syndrome
- • Testicular injury/surgery
- • Orchitis
- • Chemotherapy/radiation
- • Cryptorchidism
Secondary Hypogonadism
Low T + Low/Normal LH (pituitary/hypothalamic)
- • Pituitary tumors
- • Kallmann syndrome
- • Opioid use
- • Obesity
- • Glucocorticoid excess
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