The problem with "total testosterone"
A standard testosterone blood test measures total testosterone — the sum of all testosterone in the bloodstream, whether bound to proteins or free. Most testosterone (approximately 97–98%) is bound to proteins: primarily sex hormone-binding globulin (SHBG) and albumin. Only the unbound fraction — free testosterone — can enter cells and exert biological effects.
This distinction matters clinically. A man with a total testosterone of 450 ng/dL (within most laboratories' reference range) and a high SHBG level may have a free testosterone of 8 pg/mL — below the threshold associated with symptoms. A man with the same total testosterone but a low SHBG may have free testosterone of 15 pg/mL — entirely normal. The number in the report may be identical; the clinical situation is opposite.
The Yadav et al. 2019 study from Sir Ganga Ram Hospital found testosterone deficiency syndrome (TDS) in 48.18% of Indian men aged 40 and above using symptomatic and biochemical criteria — a figure substantially higher than the 5–10% typically cited from Western population studies. Indian men appear to have lower mean testosterone levels than Western counterparts, potentially related to metabolic comorbidity burden, and SHBG profiles in Indian men may differ as well.
What should be measured
A complete hormonal evaluation for a man with suspected testosterone deficiency includes:
Total testosterone. The starting point. Morning sampling is preferred, as testosterone follows a diurnal variation — levels are highest between 7 and 10 AM and can be 30–40% lower in the afternoon. A result obtained at 4 PM may be falsely low.
SHBG (sex hormone-binding globulin). Required to interpret free testosterone. SHBG is elevated by aging, liver disease, hyperthyroidism, and certain medications. It is suppressed by insulin resistance, hypothyroidism, and obesity. Without SHBG, it is not possible to know what proportion of total testosterone is biologically available.
Calculated or measured free testosterone. Calculated free testosterone using the Vermeulen formula (which requires total testosterone, SHBG, and albumin) is the most widely available approach. Direct measurement of free testosterone by equilibrium dialysis is more accurate but less commonly available in Indian laboratories.
LH (luteinising hormone) and FSH. These pituitary hormones distinguish primary hypogonadism (testes failing to respond despite adequate hormonal stimulation — high LH, low testosterone) from secondary hypogonadism (pituitary failing to send adequate signals — low LH, low testosterone). This distinction has direct management implications.
Prolactin. Elevated prolactin suppresses LH and testosterone. A pituitary prolactinoma can present as testosterone deficiency and must be identified before testosterone supplementation is considered.
Full metabolic panel. Testosterone deficiency is strongly associated with insulin resistance, type 2 diabetes, and metabolic syndrome in Indian men. The metabolic workup is not separate from the hormonal workup — it is part of the same clinical picture.
How testosterone deficiency affects sexual function
Testosterone's role in male sexual function is specific. It is primarily responsible for:
Libido (sexual desire). Testosterone is the primary hormonal driver of sexual desire in men. Reduced libido is among the most sensitive and specific symptoms of testosterone deficiency.
Nocturnal and morning erections. The frequency and quality of spontaneous erections — those not associated with sexual stimulation — is testosterone-dependent. A reduction in nocturnal erections is a clinical indicator of testosterone deficiency.
Mood and motivation. Testosterone has central nervous system effects on mood, motivation, and energy. Men with testosterone deficiency frequently describe a loss of drive and competitive impulse that goes beyond fatigue.
Erectile function. Testosterone contributes to erectile function through direct effects on penile nitric oxide synthase activity and through its effects on the central sexual response. However, testosterone deficiency as the sole cause of ED is less common than its contribution as a compounding factor. Men with ED and testosterone deficiency who are treated only with PDE5 inhibitors often show a suboptimal response until testosterone is also addressed.
The relationship between metabolic disease and testosterone
The relationship between testosterone and metabolic disease is bidirectional. Low testosterone promotes visceral fat accumulation and insulin resistance. Visceral adiposity reduces testosterone through increased aromatase activity (which converts testosterone to oestrogen) and through inflammatory mechanisms. This creates a cycle: the metabolic consequences of testosterone deficiency worsen the metabolic conditions that caused or contributed to the deficiency.
Breaking this cycle often requires addressing both sides — hormonal and metabolic — simultaneously.