Blood Spot LCMS Hormones 3 with SHBG

Testosterone is the principal androgen in males, synthesised predominantly by Leydig cells under luteinising-hormone control, with smaller contributions from the adrenal cortex. It circulates largely bound to sex hormone-binding globulin and albumin, with a free fraction of one to two per cent. Dried-blood-spot collection captures total testosterone concentration from capillary blood, which correlates well with venous serum when measured by LCMS but requires method-specific reference intervals.

Total testosterone is the cornerstone of male hypogonadism assessment and is also measured in females to investigate hyperandrogenic conditions. LCMS offers superior accuracy and sensitivity at low concentrations compared with immunoassay, making dried-blood-spot LCMS particularly useful when venepuncture access is limited or when precise quantitation is needed in women and children.

Oestradiol is synthesised by aromatisation of testosterone in multiple tissues — granulosa cells in women, Leydig and Sertoli cells in men, and peripheral adipose and other sites in both sexes. It signals through oestrogen receptors to regulate reproductive function, bone density, lipid metabolism, and vascular health. In men, oestradiol is essential for bone maturation and libido but excess may reflect increased aromatase activity or exogenous androgen use.

In males, oestradiol is monitored to detect excessive aromatisation during testosterone therapy and to assess gynaecomastia or hypogonadotropic hypogonadism. In females it tracks ovarian function, the menstrual cycle, and menopausal transition. LCMS quantitation is preferred when concentrations are low or when immunoassay interference is suspected.

DHEA-S is the sulphated, circulating reservoir form of dehydroepiandrosterone, produced almost exclusively by the zona reticularis of the adrenal cortex. It has a long half-life, shows minimal diurnal variation, and serves as a precursor for peripheral conversion to testosterone and oestrogens. Dried-blood-spot DHEA-S correlates closely with serum values.

DHEA-S is a marker of adrenal androgen output, assessed in adrenal insufficiency, polycystic ovary syndrome, and adrenal tumours. It declines with age and is sometimes used as a proxy for 'adrenal reserve' in functional and integrative practice, though clinical interventions based on isolated low DHEA-S remain contested.

SHBG is a liver-synthesised glycoprotein that binds testosterone and oestradiol with high affinity, modulating their bioavailability. Its production is increased by oestrogens and thyroid hormone and suppressed by androgens, insulin, and obesity. SHBG concentration influences the free fraction of sex steroids and is an independent marker of insulin sensitivity and metabolic health.

SHBG is central to interpreting total testosterone — low SHBG (common in obesity and insulin resistance) reduces total testosterone but may preserve free testosterone, while high SHBG (seen in hyperthyroidism, ageing, or liver disease) raises total testosterone but can lower free levels. The ratio of total testosterone to SHBG approximates free androgen status when direct free-testosterone measurement is unavailable.

The free androgen index is a calculated ratio of total testosterone (in nmol/L) to SHBG (in nmol/L), multiplied by 100, that estimates bioavailable androgen activity when direct free-testosterone assays are not performed. It correlates with free testosterone but is not a direct measure and may be misleading when SHBG is at physiological extremes.

FAI is used primarily to assess hyperandrogenism in women and to gauge androgen bioavailability in men with borderline total testosterone. It is more informative than total testosterone alone when SHBG is abnormal, though direct measurement of free testosterone by equilibrium dialysis or tracer methods is the reference standard.