Normal LH/FSH + Normal Total Testosterone + Low Free Testosterone

Pathophysiology

• 2-4% free (unbound, immediately bioavailable)
• 44-65% SHBG-bound (tightly bound, biologically inactive)
• 33-50% albumin-bound (weakly bound; dissociates readily - considered "bioavailable")

Causes of Elevated SHBG Leading to This Pattern

How to Proceed: Diagnostic Workup

• Measure free testosterone by equilibrium dialysis (gold standard) - direct immunoassay methods are unreliable.
• Alternatively, calculate free testosterone from total testosterone + SHBG + albumin using the Vermeulen equation.
• Free testosterone <225 pmol/L is associated with hypogonadism per EAU 2024 guidance.

• Will typically be elevated, explaining the discordance between total and free testosterone.

• Thyroid function tests (TSH, T3/T4) - rule out hyperthyroidism
• Liver function tests + hepatitis screen
• Review medications (anticonvulsants, exogenous estrogens)
• Consider age-related late-onset hypogonadism (LOH) if >40 years old

• Endocrine Society guidelines recommend diagnosing testosterone deficiency only when biochemical findings are accompanied by symptoms. If the patient is symptomatic + low free T, treatment is warranted even if total T is normal.

Symptoms of Low Free Testosterone (androgen deficiency)

Sexual/Reproductive

• Decreased libido (most specific symptom)
• Erectile dysfunction / reduced erectile quality
• Oligospermia or azoospermia
• Testicular atrophy (variable)

Metabolic/Musculoskeletal

• Decreased muscle mass and strength
• Increased fat mass (especially central/visceral)
• Decreased bone mineral density → risk of osteopenia/osteoporosis
• Reduced exercise tolerance

Neuropsychiatric

• Fatigue and low energy
• Depressed mood, irritability
• Poor concentration and cognitive performance
• Reduced motivation and "enjoyment of life"

Other

• Anemia (normocytic)
• Sleep disturbances
• Hot flashes (less common in men than women)
• Gynecomastia (especially if estrogen:androgen ratio is elevated)

Treatment Modalities

1. Treat the Underlying Cause (First Priority)

• Correct hyperthyroidism - normalizing thyroid function can reduce SHBG and restore free testosterone
• Manage liver disease
• Substitute/discontinue SHBG-elevating medications if possible
• Weight loss (if applicable) - while obesity lowers SHBG, achieving ideal weight generally improves the androgen milieu

2. Lifestyle Modification

• Weight reduction and resistance exercise
• Adequate sleep (testosterone and SHBG have diurnal variation)
• Alcohol limitation (alcohol promotes SHBG)
• Stress reduction

3. Testosterone Replacement Therapy (TRT)

4. SERMs (Selective Estrogen Receptor Modulators)

• Clomiphene citrate (off-label) - blocks estrogen negative feedback at the hypothalamus, increases LH/FSH and endogenous testosterone production.
• Useful in men who wish to preserve fertility, as TRT suppresses spermatogenesis.
• Not licensed for testosterone deficiency in most countries.

5. Aromatase Inhibitors

• Anastrozole, letrozole (off-label) - reduce peripheral conversion of testosterone to estradiol.
• Can modestly raise free testosterone by reducing estrogen-mediated SHBG upregulation.
• Limited evidence; not first-line.

Monitoring on TRT

• Serum testosterone (free + total): 3-6 months after initiation, then annually. Target mid-normal range.
• PSA + digital rectal examination: before starting, at 3-6 months, then annually.
• Hematocrit/hemoglobin: elevated erythropoiesis is the most common dose-dependent side effect. Hold if hematocrit >54%.
• Bone mineral density: DEXA at baseline if osteopenia suspected; recheck in 1-2 years.
• Liver function (if using oral agents).
• Lipid panel and cardiovascular risk assessment.

Contraindications to TRT

• Known or suspected prostate cancer
• Breast cancer in men
• Polycythemia (Hct >54%)
• Untreated obstructive sleep apnea
• Severe lower urinary tract symptoms (IPSS >19)
• Desire for fertility in the near term
• Recent MI or stroke (<6 months)
• Uncontrolled heart failure
• Thrombophilia

Summary Algorithm

Normal LH/FSH + Normal Total T + Low Free T
              ↓
Measure SHBG → likely ELEVATED
              ↓
Identify cause: age / hyperthyroidism / liver disease / medications
              ↓
Assess symptoms (libido, energy, mood, muscle mass, ED, bone density)
              ↓
      Symptomatic?
      ├─ YES → Treat underlying cause + lifestyle modification first
      │         → If insufficient: TRT (gel/patch/injection based on preference)
      └─ NO  → Monitor annually; no pharmacologic treatment needed

Recent evidence note: A 2024 review (PMID 39445719, Curr Opin Endocrinol Diabetes Obes) highlights that calculated free testosterone has both advantages and limitations and should be interpreted alongside clinical context, not used as the sole treatment trigger.