SHBG

Overview

Sex hormone–binding globulin (SHBG) is a glycoprotein produced mainly by the liver that binds circulating sex steroids, especially testosterone and estradiol, thereby regulating their free (biologically active) fractions in blood. It plays an important role in modulating androgen and estrogen action at target tissues and is influenced by hormonal, metabolic, and liver status. Elevated SHBG levels can be seen in hyperthyroidism, estrogen therapy, liver disease, and certain genetic conditions, while low levels are associated with obesity, insulin resistance, type 2 diabetes, hypothyroidism, and hyperandrogenic states such as polycystic ovary syndrome. Clinically, SHBG measurement helps interpret total testosterone and estradiol levels, estimate free hormone concentrations, and evaluate disorders of androgen excess or deficiency in both men and women.

Clinical Use Cases

  • Refining assessment of androgen deficiency in men when total testosterone is borderline.
  • Evaluating hyperandrogenism and polycystic ovary syndrome in women.
  • Estimating free testosterone or free estradiol via calculated indices.
  • Assessing effects of thyroid disease, liver disease, obesity, or insulin resistance on sex steroid status.
  • Monitoring impact of oral estrogens, anabolic steroids, or other hormone therapies on sex hormone availability.

Specimen Types

  • Serum.
  • Plasma (laboratory-dependent).

Measurement Methods

  • Automated immunoassays (chemiluminescent, electrochemiluminescent).
  • Enzyme-linked immunosorbent assays (ELISA).
  • Radioimmunoassay (older method, still used in some laboratories).

Test Preparation and Influencing Factors

  • Typically no fasting required (some labs may prefer morning sampling with sex steroids).
  • Oral estrogens (e.g., combined oral contraceptives, hormone therapy) increase SHBG levels.
  • Androgens, anabolic steroids, glucocorticoids, and insulin resistance decrease SHBG.
  • Thyroid status, liver function, age, and body mass index significantly influence SHBG concentrations.
  • Pregnancy and puberty alter SHBG levels due to changing sex steroid and thyroid hormone milieu.

Synonyms

  • Sex hormone–binding globulin.
  • Sex steroid–binding globulin.
  • Testosterone–estradiol–binding globulin (TEBG).

Further Reading

  • “Sex Hormone–Binding Globulin (SHBG) Test” – MedlinePlus – 3