Normal Testosterone and SHBG Ranges for a 45-Year-Old Male
For a 45-year-old male, normal total testosterone ranges from approximately 300-800 ng/dL, with free testosterone typically between 120-368 pg/mL (using equilibrium dialysis), and SHBG levels vary but are essential to measure when evaluating borderline testosterone levels. 1, 2
Total Testosterone Reference Ranges
The standard adult male range for total testosterone is 300-800 ng/dL in most laboratories, though this represents significant variability across testing facilities 1
For men specifically in their 40s, the 2.5th to 97.5th percentile range is 251-914 ng/dL (8.7-31.7 nmol/L), based on data from apparently healthy men 3
The lower threshold of 300 ng/dL is widely accepted as the cutoff below which hypogonadism should be suspected, requiring repeat morning testing between 8-10 AM for confirmation 1, 4
Laboratory reference values vary dramatically—with reported lower limits ranging from 130 to 450 ng/dL across different facilities, representing a 350% difference 5
Free Testosterone Reference Ranges
Free testosterone measured by standardized equilibrium dialysis in healthy men aged 19-39 years ranges from 120-368 pg/mL (415-1274 pmol/L), which serves as the reference for younger adults 2
For all adult men (19+ years), the normative range is 66-309 pg/mL (229-1072 pmol/L), though this includes age-related decline 2
Calculated free testosterone using the Vermeulen equation in men aged 20-45 years ranges from 0.245-0.785 nmol/L, though different calculation methods yield substantially different results 6
Free testosterone represents approximately 2% of total testosterone, with the remainder bound to SHBG and albumin 6
Sex Hormone-Binding Globulin (SHBG) Considerations
SHBG levels directly influence total testosterone concentrations, and low SHBG (common in obesity) can artificially lower total testosterone while free testosterone remains normal 1, 4
When evaluating low total testosterone in men with obesity, measuring morning serum free testosterone by equilibrium dialysis is essential to distinguish true hypogonadism from SHBG-related decreases 1
SHBG measurement is particularly important when total testosterone is borderline (near 300 ng/dL), as it helps determine whether free testosterone is truly low 4
Free testosterone levels are negatively associated with body mass index, age, and SHBG levels, meaning these factors must be considered when interpreting results 2
Critical Clinical Caveats
Testosterone levels must be drawn in the morning (8-10 AM) on two separate occasions to confirm hypogonadism, as single measurements are insufficient due to diurnal variation and assay variability 4, 3
Age-related decline is expected—men in their 40s have higher reference ranges than older men, with the lower threshold dropping from 251 ng/dL in the 40s to 216 ng/dL in the 50s 3
Health status significantly impacts testosterone levels—chronic disease, high BMI (>29 kg/m²), and certain medications lower testosterone, while smoking paradoxically increases it 3
Direct measurement of free testosterone by equilibrium dialysis is the gold standard, as analog immunoassays are unreliable and remain influenced by SHBG even when measuring "free" testosterone 7
Calculated free testosterone values vary considerably depending on which equation is used (Sodergard, Vermeulen, Nanjee-Wheeler, or Ly-Handelsman), with mean biases ranging from 5.8% to 56.0% 6
The free androgen index (total testosterone/SHBG ratio) correlates poorly with calculated free testosterone (r²=0.21-0.46) and overestimates free testosterone at low SHBG concentrations 6