Testosterone In Serum
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Contents |
Introduction
- Testosterone in Serum or Plasma (see [3] 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 [6]
- evaluation of virilization in women
Reference-interval
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
- estrogen therapy
- Klinefelter's syndrome
- hypopituitarism
- testicular feminization
- hepatic cirrhosis
- andropause*
- levels drop in men with children
- * 40% of men > 45 years of age [4]
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 : 100 uL of specimen is the minimum volume required to perform the assay.
More General Terms
Additional Terms
References
- Diagnostic Products Corporation, 5700 West 96th Street, CA 90045, January 6, 1988.
- Henry, John Bernard., Evaluation of Endocrine Function, Clinical Diagnosis & Management, W.B. Saunder Co., Philadelphia, 1984, pp. 305-312
- Wang C et al, J Clin Endocrinol Metab 89:534, 2004 PMID: [1]
- Internal Medicine News, July 2005, pg 1,22
- Gray, P cited in Netscape Dec 22, 2005
- Anawalt BD et al. Performance of total testosterone measurement to predict free testosterone for the biochemical evaluation of male hypogonadism. J Urol 2012 Apr; 187:1369. PMID: [2]
