In a male with low libido, a normal free testosterone result but markedly elevated sex hormone‑binding globulin (~99 nmol/L), is the free testosterone likely truly normal?

Elevated SHBG with "Normal" Free Testosterone: Is Your Free T Truly Okay?

Your free testosterone is very likely NOT truly normal despite the lab report, and your low libido symptoms strongly suggest you have functional hypogonadism that warrants further evaluation and likely treatment.

Why Your Free Testosterone Result Is Probably Wrong

Your SHBG of 99 nmol/L is extremely elevated—more than double the upper limit of normal and in the top 5% of all men presenting to men's health clinics 1. This creates a critical problem: most "free testosterone" assays used by commercial laboratories are direct immunoassays that are notoriously inaccurate and unreliable 2, 3. When SHBG is markedly elevated like yours, these assays systematically overestimate free testosterone, giving falsely reassuring results 2, 3.

The Gold Standard You Probably Didn't Get

• True free testosterone must be measured by equilibrium dialysis performed for 16 hours at 37°C using undiluted serum, followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) 2, 4.
• This method is the only FDA-cleared accurate approach but is not available at most commercial laboratories 5, 2.
• The direct immunoassay your lab likely used has no clinical validity when SHBG is abnormal 2, 3.

What Your Numbers Actually Mean

With SHBG at 99 nmol/L, the overwhelming majority of your testosterone is tightly bound and biologically unavailable 3. Even if your total testosterone appears "normal," your bioavailable fraction is almost certainly low 1, 3. Here's why:

• In healthy non-obese men aged 19-39, the reference range for free testosterone by equilibrium dialysis is 120-368 pg/mL 4.
• For all adult men, the range is 66-309 pg/mL 4.
• Your actual free testosterone is likely well below these thresholds despite what the lab report says 2, 3.

The Free Androgen Index Alternative

Since you probably cannot access equilibrium dialysis, calculate your free androgen index (FAI) using this formula 5:

FAI = (Total Testosterone ÷ SHBG) × 100

• An FAI < 30 strongly suggests true hypogonadism even when total testosterone appears borderline-normal 5.
• This calculation avoids the inaccuracy of direct immunoassays 5, 3.

Your Symptoms Are the Key Clinical Evidence

Diminished libido is the primary symptom that justifies testosterone evaluation and treatment 6. The fact that you have low libido with markedly elevated SHBG creates a high pre-test probability of true biochemical hypogonadism 5, 6.

What the Evidence Shows About Symptoms

• Low libido and erectile dysfunction are the only symptoms with proven benefit from testosterone therapy (standardized mean difference 0.35) 6.
• Fatigue, low energy, and mood symptoms show minimal to no improvement with testosterone therapy 6.
• Your symptom profile (low libido) is the exact indication for which testosterone therapy works 6.

The Diagnostic Algorithm You Need to Follow

Step 1: Confirm True Hypogonadism

1. Obtain two separate morning total testosterone measurements (8-10 AM) on different days 6, 2.
2. Calculate your free androgen index using the formula above 5.
3. If available, request free testosterone by equilibrium dialysis (not direct immunoassay) 2, 4.
4. Measure LH and FSH to distinguish primary from secondary hypogonadism 6.

Step 2: Interpret Your Results

• If total testosterone < 300 ng/dL on both measurements: you have confirmed hypogonadism regardless of the free testosterone assay 6.
• If total testosterone is 231-346 ng/dL (gray zone) AND FAI < 30: you likely have functional hypogonadism from elevated SHBG 5, 6.
• If total testosterone > 350 ng/dL but FAI < 30 with low libido: you have SHBG-mediated functional hypogonadism that may warrant treatment 5, 3.

Why Elevated SHBG Matters Clinically

The Binding Protein Problem

• SHBG binds testosterone with extremely high affinity, rendering the bound fraction biologically unavailable to tissues 3.
• Only free and albumin-bound testosterone can enter cells and exert androgenic effects 3.
• With SHBG at 99 nmol/L, you have a massive reservoir of bound, inactive testosterone 1, 3.

What Causes Elevated SHBG

• Aging is the most common cause—SHBG rises progressively with age 1.
• Liver disease (cirrhosis) causes marked SHBG elevation 5.
• Hyperthyroidism increases SHBG production 5.
• Genetic variation accounts for wide inter-individual differences 1.

Treatment Implications

If Hypogonadism Is Confirmed

Testosterone replacement therapy is indicated for men with confirmed biochemical hypogonadism and diminished libido 6. Expected outcomes include:

• Small but significant improvements in sexual function and libido (standardized mean difference 0.35) 6.
• Modest quality of life improvements, primarily in sexual domains 6.
• Little to no effect on energy, physical function, or mood 6.

Monitoring During Treatment

• Testosterone therapy will lower your SHBG from its current elevated level 7.
• In men with initially elevated SHBG (like Klinefelter's patients with SHBG 16 ng/mL), testosterone therapy **reduced SHBG to normal levels (4 ng/mL)** 7.
• This SHBG reduction amplifies the increase in free testosterone, improving bioavailability 7.

Critical Contraindications

• If you desire fertility preservation, testosterone therapy is absolutely contraindicated 6.
• Instead, you would need gonadotropin therapy (hCG plus FSH) to stimulate endogenous production 6.
• Active prostate or breast cancer, hematocrit > 54%, or recent cardiovascular events are absolute contraindications 6.

Common Pitfalls to Avoid

• Do not accept a "normal" free testosterone result from a direct immunoassay when SHBG is elevated—the result is almost certainly wrong 2, 3.
• Do not diagnose or exclude hypogonadism based on a single testosterone measurement—two morning values are required 6, 2.
• Do not ignore symptoms when total testosterone is borderline and SHBG is markedly elevated—calculate FAI or measure true free testosterone 5, 3.
• Do not assume testosterone therapy will improve energy or mood—the evidence shows benefit only for sexual function 6.

Bottom Line

With SHBG at 99 nmol/L and low libido, you almost certainly have functional hypogonadism with falsely reassuring free testosterone results. Repeat morning total testosterone on two occasions, calculate your free androgen index, and measure LH/FSH to confirm the diagnosis and guide treatment 5, 6, 2. If confirmed, testosterone therapy is likely to improve your libido and sexual function 6.