Testosterone is responsible for the development of male secondary sexual characteristics. It is secreted by the adrenal glands and testes in men and by the adrenal glands and ovaries in women. Excessive production induces premature puberty in men and masculinity in women. Testosterone exists in serum as both unbound (free) fractions and bound fractions to albumin: sex hormone–binding globulin and testosterone-binding globulin. Unbound (free) testosterone is the active portion. Testosterone levels undergo large and rapid fluctuations; levels peak in early morning in males. Females show a cyclic elevation 1–2 days midcycle.

Testosterone measurements in men assess hypogonadism, pituitary gonadotropin function, impotency, and cryptorchidism; these measurements are also useful in the detection of ovarian tumors and hirsutism in women. In prepubertal boys, they can assess sexual precocity. This test may be part of a fertility workup in association with chronic anovulation caused by polycystic ovary syndrome. It can also detect ovarian and adrenal tumors in women with symptoms of hirsutism and amenorrhea.

Reference values are method-dependent.

Total Testosterone:

• Men: 270–1070 ng/dL or 9–38 nmol/L (values in older men diminish moderately)

• Women: 15–70 ng/dL or 0.52–2.4 nmol/L

• Postmenopausal women: 8–35 ng/dL or 0.3–1.2 nmol/L (half of normal)

• Pregnant women:

  • First trimester: 26–211 ng/mL or 0.9–7.32 mmol/L

  • Second trimester: 34–243 ng/dL or 1.2–8.4 mmol/L

  • Third trimester: 63–309 ng/mL or 2.2–10.7 mmol/L

Children:

Free Testosterone:

• Men: 50–210 pg/mL or 174–729 pmol/L

• Women: 1.0–8.5 pg/mL or 3.5–29.5 pmol/L

• Children:

  • Boys: 0.1–3.2 pg/mL or 0.3–11.1 pmol/L

  • Girls: 0.1–0.9 pg/mL or 0.3–3.1 pmol/L

• Puberty:

  • Boys: 1.4–156 pg/mL or 4.9–541 pmol/L

  • Girls: 1.0–5.2 pg/mL or 3.5–18.0 pmol/L

1. Obtain a 5-mL venous blood sample (red-topped tube); serum is preferred. Observe standard precautions. Label the specimen with the patient’s name, date and time of collection, and test(s) ordered. Place the specimen in a biohazard bag.

2. Indicate age and gender on laboratory requisition.

1. Males: Decreased total testosterone levels occur in the following conditions:

   1. Hypogonadism (pituitary failure)

   2. Klinefelter syndrome

   3. Hypopituitarism (primary and secondary)

   4. Orchidectomy

   5. Hepatic cirrhosis

   6. Down syndrome

   7. Delayed puberty

2. Males: Decreased free testosterone levels occur in hypogonadism and older men.

3. Males: Increased total testosterone levels occur in the following conditions:

   1. Hyperthyroidism

   2. Syndromes of androgen resistance

   3. Adrenal tumors

   4. Precocious puberty and adrenal hyperplasia in boys

   5. Testosterone resistance syndrome

4. Females: Increased total testosterone levels are associated with the following conditions:

   1. Adrenal neoplasms

   2. Ovarian tumors, benign or malignant (virilizing)

   3. Trophoblastic disease during pregnancy

   4. Idiopathic hirsutism

   5. Hilar cell tumor

5. Females: Increased free testosterone levels are associated with the following conditions:

   1. Female hirsutism

   2. Polycystic ovary syndrome

   3. Virilization

Pretest Patient Care

1. Explain test purpose and procedure. Draw blood at 7:00 a.m. (0700 hours) for highest levels.

2. Draw multiple pooled samples at different times throughout the day if necessary for more reliable results.

3. Do not administer radioisotopes within 1 week before test.

4. Follow guidelines in Chapter 1 regarding safe, effective, informed pretest care.

1. Alcoholism in males decreases testosterone levels.

2. Estrogen therapy increases testosterone levels (see Appendix E).

3. Many drugs, including androgens and steroids, decrease testosterone levels (see Appendix E).