Unit Converter
Sex hormone‑binding globulin (SHBG)

SI UNITS (recommended)

CONVENTIONAL UNITS

(Major Carrier Protein for Testosterone & Estradiol - Essential for Calculating Free Hormones & Evaluating Androgen Disorders)

Synonyms

  • SHBG
  • Sex hormone–binding globulin
  • Testosterone–binding globulin
  • Androgen-binding protein (distinct but related)
  • TeBG / SSBG (older)

Units of Measurement

  • nmol/L
  • µg/mL
  • µg/dL
  • µg/100 mL
  • µg%
  • µg/L
  • mg/L

Unit Conversions

Molecular weight of SHBG ≈ 100,000–120,000 Da

(Common reference MW = 118 kDa)

Using 118 kDa:

nmol/L ↔ mg/L

1 nmol/L=118 mg/L1\ \text{nmol/L} = 118\ \text{mg/L}1 nmol/L=118 mg/L 1 mg/L=0.00847 nmol/L1\ \text{mg/L} = 0.00847\ \text{nmol/L}1 mg/L=0.00847 nmol/L

µg/mL ↔ mg/L

1 µg/mL=1 mg/L1\ \text{µg/mL} = 1\ \text{mg/L}1 µg/mL=1 mg/L

µg/dL → µg/L

1 µg/dL=10 µg/L1\ \text{µg/dL} = 10\ \text{µg/L}1 µg/dL=10 µg/L

µg% = µg/dL

Description

SHBG is a glycoprotein produced mainly by the liver that binds:

  • Testosterone (highest affinity)
  • Dihydrotestosterone (DHT)
  • Estradiol (E2)

SHBG controls the bioavailability of sex steroids.
Only free + albumin-bound testosterone is considered bioavailable.
Thus, SHBG is crucial for:

  • Evaluating male hypogonadism
  • Assessing androgen excess in women
  • Interpreting total testosterone correctly
  • Calculating free testosterone (FT) via Vermeulen equations

Physiological Role

  • Regulates free sex-hormone levels
  • Ensures stable circulating testosterone
  • Influences adiposity, insulin sensitivity, and metabolic risk
  • Acts as a biomarker of liver function and metabolic health

Clinical Significance

HIGH SHBG

Causes

  • Hyperthyroidism
  • Pregnancy (estrogen effect)
  • Oral contraceptives
  • Liver disease (cirrhosis)
  • HIV infection
  • Aging
  • Estrogen therapy
  • Anorexia / malnutrition

Effects

  • Low free testosterone
  • Symptoms of hypogonadism despite normal total testosterone

LOW SHBG

Highly clinically relevant

Causes

  • Obesity
  • Insulin resistance
  • Metabolic syndrome
  • Type 2 diabetes
  • Hypothyroidism
  • PCOS (women)
  • Androgen excess
  • Nephrotic syndrome
  • High-dose steroids
  • Acromegaly

Effects

  • Higher free testosterone
  • In women → hirsutism, acne, PCOS-like symptoms
  • In men → preserved FT despite low total T

Reference Intervals

(Tietz 8E + Endocrine Society + Mayo + ARUP)
 Ranges vary by age & sex.

Adult Men

  • 10 – 57 nmol/L

Adult Women

  • 18 – 144 nmol/L

Postmenopausal Women

  • 20 – 120 nmol/L

Children

  • Levels are generally low until puberty.

Clinical Flags

  • SHBG < 15 nmol/L → strongly suggests insulin resistance or androgen excess
  • SHBG > 100 nmol/L → suspect hyperthyroidism, estrogen effect, pregnancy

Diagnostic Uses

1. Evaluation of Hypogonadism

Calculate free or bioavailable testosterone using SHBG:

  • Total T may be “normal” but FT low due to high SHBG.

2. PCOS Evaluation (Women)

Low SHBG → high free androgen index (FAI).

3. Estrogen Status

Elevated SHBG reflects estrogen effect:

  • Pregnancy
  • OCP use
  • HRT

4. Thyroid Disorders

SHBG ↑ with hyperthyroidism, ↓ with hypothyroidism.

5. Liver Disease

Cirrhosis → ↑ SHBG.

6. Metabolic Disorders

Low SHBG is a biomarker of:

  • Metabolic syndrome
  • NAFLD
  • Insulin resistance

7. Aging

SHBG increases with age, lowering free T.

Analytical Notes

  • Fasting not required
  • Measured using immunoassays (chemiluminescence)
  • Variability exists between platforms
  • FT calculation should use same SHBG assay values
  • Abnormal SHBG changes FT more than total T levels

Clinical Pearls

  • Free testosterone should NEVER be interpreted without SHBG.
  • Obesity → low SHBG → misleadingly normal free T despite low total T.
  • Estrogen therapy ↑ SHBG → decreases free T → drives breast tenderness, libido changes.
  • In PCOS, low SHBG is one of the earliest metabolic abnormalities.
  • SHBG is a strong predictor of type 2 diabetes risk in both men and women.

Interesting Fact

Although SHBG is best known as a sex-hormone transporter, it also has receptors on cell membranes, suggesting additional signaling roles beyond hormone transport.

Reference

  1. Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Hormone Binding Proteins
  2. Endocrine Society Clinical Guidelines - Male Hypogonadism & PCOS
  3. Mayo Clinic Laboratories - SHBG
  4. ARUP Consult - SHBG & Testosterone Interpretation
  5. NIH / MedlinePlus - SHBG Test
  6. AACE - Endocrinology Guidelines

Last updated: January 27, 2026

Reviewed by : Medical Review Board

Change language

Other Convertors