testosterone in serum

Introduction

Testosterone in Serum or Plasma (see for comparison of methods)

Indications

• evaluation of hypogaonadism in males
  • levels < 150 ng/dL or > 350 ng/dL identify or exclude biochemical hypogonadism reasonably accurately
    • when levels fall between these thresholds, consider serum free testosterone
• evaluation of virilization in women

Contraindications

• normal testes, no gynecomastia, & regular morning erections

Reference interval

• testosterone levels in men vary diurnally
  • highest levels in the morning
  • diurnal variation declines with ages
  • in young men, mean levels are
    • 600 ng/dL at 7 am
    • 500 ng/dL at 10 am
    • 400-450 ng/dL at 2 pm
  • after age 45, mean testosterone levels do not differ between 7 AM to 2 PM
• 8 AM serum testosterone levels vary with the season
  • serum testosterone is lowest in spring & summer & higher in fall & winter
  • lowest mean level is in May (440 mg/dL) & highest in January (600 ng/dL)
• Male: 270-1070 ng/dL
• Female: 60- 86 ng/dL
• Pre-Pubertal
  • Female: 0-30 ng/dL
  • Male: 1-120 ng/dL
• reference intervals reported by different laboratories differ
  • lower limits range from 160-300 ng/dL
  • upper limits range from 726-1130 ng/dL

Principle

The Coat-A-Count procedure is a solid-phase radioimmunoassay, wherein I-125 labeled Testosterone competes for a fixed time with Testosterone in the patient sample for sites on Testosterone- specific antibody. This reaction takes place in the presence of blocking agents which serve to liberate bound Testosterone from free. The antibody being immobilized to the wall of a poly- propylene tube decanting the supernatant suffices to terminate the competition & to isolate the antibody-bound fraction of the radiolabeled Testosterone. Counting the tube in the gamma counter then yields a number, which converts by way of a calibration curve to a measure of the Testosterone present in the patient sample.

Clinical significance

In the male, testosterone is mainly synthesized in the interstitial Leydig cells & the testis, & is regulated by the interstitial cell stimulating hormone (ICSH), or luteinizing hormone (LH) of the anterior pituitary (the female equivalent of ICSH). The pulsatile nature of LH secretions results in pulsatile secretions of testosterone.

Testosterone is responsible for the development of secondary sex characteristics, such as the accessory sex organs, the prostate, seminal vesicles & growth offacial, pubic & axillary hair. Testosterone measurements have been very helpful in evaluating hypogonadal states.

In the female, testosterone levels are normally found to be much lower than those encountered in the normal male. Testosterone in the female comes from 3 sources. It is secreted in small quantities by both the adrenal glands & the ovaries, & in normal women 50-60% of the daily testosterone production arises from peripheral metabolism of prehormones chiefly androstenedione.

Virilization in women is associated with the administration of androgens. There appears to be a correlation between serum testosterone levels & the degree of virilization in women, although approximately 25% of women with varying degrees of virilism have serum testosterone levels that fall within the normal female range.

Increases

females:

• polycystic ovary syndrome (female)

Decreases

males

• hypogonadism
• orchidectomy
• pharmaceuticals
  • estrogen therapy
  • opioids
  • high-dose glucocorticoids
• Klinefelter's syndrome
• hypopituitarism
• testicular feminization
• hepatic cirrhosis
• andropause*
• levels drop in men with children

* 40% of men > 45 years of age

Specimen

• Serum or heparinized or EDTA plasma may be used. When serial samples are being evaluated, the same type of specimen should be used throughout the study.
• If assay is performed within 24 hours after collection, the specimen should be stored in the refrigerator at 2-8*C. If the testing will be delayed more than 24 hours, the specimen should be frozen. Mix thoroughly after thawing to ensure consistency in the results. Avoid repeated freezing & thawing.
• Specimens showing particulate matter, erythrocytes, or turbidity should be centrifuged before testing.

SAMPLE VOLUME: 100 uL of specimen is the minimum volume required to perform the assay.

More general terms

• testosterone in body fluid

More specific terms

• testosterone.bound in serum/plasma

Additional terms

• androgen excess (hyperandrogenism)
• androgen insufficiency (hypoandrogenism, testosterone deficiency)
• bioavailable testosterone
• free testosterone
• testosterone (Delatestryl Testopel, Striant, Intrinsa, Xyosted)

Component of

• testosterone/epitestosterone in serum/plasma
• testosterone/cortisol in serum/plasma

Patient information

testosteone in serum patient information