Unit Converter
Testosterone
(Primary Male Sex Hormone - Essential for Puberty, Sexual Function, Fertility, Muscle Mass & General Metabolism)
Synonyms
- Testosterone
- Total testosterone
- Free testosterone (FT)
- Bioavailable testosterone
- Serum testosterone
- Androgen hormone
Units of Measurement
- nmol/L
- ng/mL
- ng/dL
- ng/100 mL
- ng%
- ng/L
- µg/L
Unit Conversions
Molecular Weight of Testosterone = 288.42 g/mol
nmol/L ↔ ng/mL
1 nmol/L=0.288 ng/mL1\ \text{nmol/L} = 0.288\ \text{ng/mL}1 nmol/L=0.288 ng/mL 1 ng/mL=3.47 nmol/L1\ \text{ng/mL} = 3.47\ \text{nmol/L}1 ng/mL=3.47 nmol/L
nmol/L ↔ ng/dL
1 nmol/L=28.8 ng/dL1\ \text{nmol/L} = 28.8\ \text{ng/dL}1 nmol/L=28.8 ng/dL 1 ng/dL=0.0347 nmol/L1\ \text{ng/dL} = 0.0347\ \text{nmol/L}1 ng/dL=0.0347 nmol/L
ng/mL ↔ ng/L
1 ng/mL=1000 ng/L1\ \text{ng/mL} = 1000\ \text{ng/L}1 ng/mL=1000 ng/L 1 ng/mL=1 µg/L1\ \text{ng/mL} = 1\ \text{µg/L}1 ng/mL=1 µg/L
ng/dL = ng%
(Older units.)
Description
Testosterone is the main circulating androgen produced primarily by:
- Leydig cells of testes (95%)
- Ovaries (small amounts)
- Adrenal glands (minor contribution)
It circulates in three forms:
- Free testosterone (~1–2%)
- Albumin-bound (~30–40%)
- SHBG-bound (~60%)
Only free + albumin-bound testosterone is bioavailable, capable of entering cells and exerting biological effects.
Physiological Role
1. Male Sexual Development
- Puberty initiation
- Testis & penis growth
- Voice deepening
- Facial/body hair
2. Reproductive Function
- Libido
- Erectile function
- Spermatogenesis
3. Metabolic & Body Composition Effects
- Increases muscle mass
- Reduces visceral fat
- Enhances erythropoiesis
- Maintains bone density
4. Mood & Cognition
- Affects confidence, motivation, memory
Clinical Significance
LOW TESTOSTERONE
Primary Hypogonadism
- High LH/FSH
Causes: - Klinefelter syndrome
- Testicular injury
- Chemotherapy
- Radiation
- Orchitis
Secondary Hypogonadism (Pituitary/Hypothalamic)
- Low/normal LH/FSH
Causes: - Pituitary tumors
- Hyperprolactinemia
- Systemic illness
- Chronic opioid use
- Obesity
- Type 2 diabetes
Symptoms of Low Testosterone
- Reduced libido
- Erectile dysfunction
- Fatigue
- Loss of muscle mass
- Central obesity
- Depression
- Low bone density
- Infertility
HIGH TESTOSTERONE
Men
- Rare unless exogenous supplementation
- Adrenal tumors
- Testicular tumors
- Androgen insensitivity (high T with feminization)
Women
- PCOS
- Congenital adrenal hyperplasia (CAH)
- Ovarian/adrenal androgen-secreting tumors
- Severe insulin resistance
- Hirsutism, acne, menstrual irregularities
Reference Intervals
(Tietz 8E + Endocrine Society + Mayo + ARUP)
Values depend on age, sex, and assay (LC–MS/MS preferred).
Adult Men (Morning Sample, 7–10 AM)
- Total Testosterone: 300 – 1000 ng/dL
(= 10.4 – 34.7 nmol/L)
Adult Women
- Total Testosterone: 15 – 70 ng/dL
(= 0.5 – 2.4 nmol/L)
Children
- Prepubertal: very low
- Puberty staging: Tanner-based values used
Free Testosterone (by Equilibrium Dialysis or Calculation)
- Men: 5 – 25 ng/dL
- Women: 0.1 – 0.9 ng/dL
Bioavailable Testosterone
- Men: 100 – 300 ng/dL
Diagnostic Uses
1. Evaluation of Male Hypogonadism
Repeat testosterone measurement required:
- Early morning
- Fasting
- Confirm with SHBG & LH/FSH
2. PCOS Evaluation (Women)
High testosterone → androgen excess workup.
3. Infertility
Low T affects spermatogenesis.
4. Monitoring Testosterone Replacement Therapy
Ensure physiologic levels, avoid supraphysiologic ranges.
5. Suspected Androgen-Secreting Tumors
Markedly elevated levels.
6. CAH Evaluation
Part of androgen pattern (with DHEA-S, androstenedione).
Analytical Notes
- Morning sample mandatory in adult men
- Fasting sample improves binding-protein consistency
- LC–MS/MS is gold standard
- SHBG assay required for accurate free T calculation
- Avoid testing during acute illness (suppresses T)
Clinical Pearls
- Testosterone should always be interpreted with LH, FSH, SHBG, and clinical context.
- Obesity lowers SHBG → low total T but normal free T.
- Aging decreases free testosterone more rapidly than total T.
- Women with PCOS often have normal total T but high free T due to low SHBG.
- Very high testosterone (>1500 ng/dL) strongly suggests exogenous use or tumor.
Interesting Fact
Women produce three times more testosterone than estrogen daily - most is converted peripherally to estradiol or inactivated.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Endocrine Chemistry
- Endocrine Society - Clinical Practice Guideline for Hypogonadism (2018)
- AACE Guidelines - Testosterone Therapy
- Mayo Clinic Laboratories - Testosterone
- ARUP Consult - Androgen Testing
- NIH / MedlinePlus - Testosterone