Can you interpret an adult male’s 8 AM labs showing total testosterone >1500 ng/dL, free testosterone >50 pg/mL, LH 0.3 mIU/mL, and FSH 0.6 mIU/mL?

Interpretation of Laboratory Results: Exogenous Testosterone Use with Suppressed Gonadotropins

These laboratory results indicate exogenous testosterone use (either therapeutic or non-prescribed) with complete suppression of the hypothalamic-pituitary-gonadal axis, not endogenous testosterone production.

Laboratory Pattern Analysis

Your results show a classic pattern of exogenous testosterone administration:

• Total testosterone >1500 ng/dL is markedly supraphysiologic and exceeds the upper limit of the normal reference range (264-916 ng/dL) by more than 60% 1
• Free testosterone >50 pg/mL is similarly elevated beyond the reference range (7.2-24.0 pg/mL) by more than 100% 1
• LH 0.3 mIU/mL is profoundly suppressed below the normal range (1.7-8.6 mIU/mL), indicating complete shutdown of pituitary luteinizing hormone secretion 1, 2
• FSH 0.6 mIU/mL is similarly suppressed below normal (1.5-12.4 mIU/mL), confirming feedback inhibition of the hypothalamic-pituitary axis 1, 2

Mechanism: Exogenous vs. Endogenous Testosterone

This hormonal pattern cannot occur with endogenous (natural) testosterone production:

• When the body produces testosterone naturally—even in cases of testicular tumors or other pathologic conditions—LH and FSH would be either normal or elevated, not suppressed 1
• The combination of supraphysiologic testosterone with profoundly suppressed LH/FSH (<0.85 mIU/mL for LH, <0.7 mIU/mL for FSH) is pathognomonic for exogenous androgen administration 2
• During exogenous testosterone administration, endogenous testosterone release is inhibited through feedback inhibition of pituitary LH, and at large doses spermatogenesis is also suppressed through feedback inhibition of pituitary FSH 3

Clinical Implications

If You Are Using Prescribed Testosterone Therapy

• These levels indicate significant overdosing or improper timing of blood draw relative to injection 1
• Peak serum testosterone occurs 2-5 days after intramuscular injection, often transiently exceeding the upper limit of normal 1
• Target testosterone levels should be mid-normal (500-600 ng/dL) when measured midway between injections (days 5-7 for weekly dosing, days 7-10 for bi-weekly dosing) 1
• Levels >1500 ng/dL carry increased risk of adverse effects, particularly erythrocytosis (elevated hematocrit), which occurs in approximately 44% of men on injectable testosterone 1

If You Are Not Prescribed Testosterone

• These results indicate use of exogenous testosterone from non-medical sources 2
• This pattern is commonly seen with injectable testosterone use (most frequently associated with significantly decreased LH/FSH <0.85/<0.7 mIU/mL), while topical testosterone use more commonly shows detectable LH/FSH 2
• Prolonged suppression of LH and FSH causes testicular atrophy and azoospermia (absence of sperm production), which may persist for months to years after discontinuation 1, 3

Immediate Recommendations

Safety Monitoring Required

• Hematocrit/hemoglobin must be checked immediately—testosterone therapy should be withheld if hematocrit exceeds 54%, and therapeutic phlebotomy considered for high-risk patients 1
• Elevated hematocrit increases blood viscosity and can exacerbate coronary, cerebrovascular, and peripheral vascular disease 1
• PSA should be measured in men over 40 years; urologic referral is indicated if PSA rises >1.0 ng/mL within the first 6 months or >0.4 ng/mL per year 1

Fertility Considerations

• If you desire future fertility, testosterone therapy must be discontinued immediately—exogenous testosterone causes prolonged and potentially irreversible azoospermia 1
• Recovery of spermatogenesis after discontinuation is highly variable and may require 6-24 months or longer 1
• Gonadotropin therapy (hCG plus FSH) is the only evidence-based approach to restore both testosterone production and sperm counts after testosterone-induced suppression 1

Dose Adjustment (If Prescribed)

• If these levels were drawn 2-5 days after injection (at peak), they do not reflect average testosterone exposure—levels should be measured midway between injections 1
• If levels remain >1500 ng/dL at the midpoint, dose reduction by 25-50% is mandatory to prevent adverse effects 1
• Consider switching from injectable to transdermal testosterone gel (1.62%, ~40 mg daily), which provides more stable day-to-day levels and reduces erythrocytosis risk from 44% to approximately 15% 1

Common Pitfalls to Avoid

• Do not draw testosterone levels at the peak (days 2-5 after injection)—supraphysiologic peaks do not reflect average exposure and may lead to inappropriate dose reduction 1
• Do not ignore mild erythrocytosis (hematocrit 50-52%) in elderly patients or those with cardiovascular disease—even modest elevations increase blood viscosity and thrombotic risk 1
• Do not continue full-dose testosterone when hematocrit exceeds 54%—this is an absolute indication to withhold therapy 1
• Never restart testosterone if fertility is desired—this will immediately suppress spermatogenesis again 1