Sorted By Test Name - Mayo Medical Laboratories

may be associated with symptoms and signs of hypogonadism in men, while decreased levels can result in
androgenization in women. SHBG levels in prepubertal children are higher than in adults. With the
increase in fat mass during early puberty they begin to fall, a process that accelerates as androgen levels
rise. Men have lower levels compared with women and nutritional status is inversely correlated with
SHBG levels throughout life, possibly mediated by insulin resistance. Insulin resistance, even without
obesity, results in lower SHBG levels. This is associated with increased intra-abdominal fat deposition
and an unfavorable cardiovascular risk profile. In postmenopausal women, it may also predict the future
development of type 2 diabetes mellitus. Androgens and norethisterone-related synthetic progesterones
also decrease SHBG in women. Endogenous or exogenous thyroid hormones or estrogens increase SHBG
levels. In men, there is also an age-related gradual rise, possibly secondary to the mild age-related fall in
testosterone production. This process can result in bioavailable testosterone levels that are much lower
than would be expected based on total testosterone measurements alone.
Useful For: Diagnosis and follow-up of women with symptoms or signs of androgen excess (eg,
polycystic ovarian syndrome and idiopathic hirsutism) An adjunct in monitoring sex-steroid and
anti-androgen therapy An adjunct in the diagnosis of disorders of puberty An adjunct in the diagnosis and
follow-up of anorexia nervosa An adjunct in the diagnosis of thyrotoxicosis (tissue marker of thyroid
hormone excess) A possible adjunct in diagnosis and follow-up of insulin resistance and cardiovascular
and type 2 diabetes risk assessment, particularly in women In laboratories without access to bioavailable
testosterone or equilibrium dialysis-based "true" free testosterone assays, sex hormone-binding globulin
measurement is crucial in cases when assessment of the free testosterone fraction (aka free androgen
index or calculated free testosterone) is required. At Mayo Medical Laboratories, both bioavailable
testosterone (TTBS/80065 Testosterone, Total and Bioavailable, Serum) and free testosterone
(TGRP/8508 Testosterone, Total and Free, Serum) measurements are available. Free testosterone
(TGRP/8508) is measured by equilibrium dialysis, obviating the need for sex hormone-binding globulin
measurements to calculate free androgen fractions.
Interpretation: Many conditions of mild-to-moderate androgen excess in women, particularly
polycystic ovarian syndrome, are associated with low sex hormone-binding globulin (SHBG) levels. Most
of these women are also insulin resistant and many are obese. A defect in SHBG production could lead to
bioavailable androgen excess, in turn causing insulin resistance that depresses SHBG levels further. There
are rare cases of SHBG mutations that clearly follow this pattern. SHBG levels are typically very low in
these individuals. However, in most patients, SHBG levels are mildly depressed or even within the lower
part of the normal range. In these patients, the primary problem may be androgen overproduction, insulin
resistance, or both. A definitive cause cannot be usually established. Any therapy that either increases
SHBG levels (eg, estrogens or weight loss), reduces bioactivity of androgens (eg, androgen receptor
antagonists, alpha-reductase inhibitors), or reduces insulin resistance (eg, weight loss, metformin,
peroxisome proliferator-activated receptor [PPAR] gamma agonists), can be effective. Improvement is
usually associated with a rise in SHBG levels, but bioavailable or free testosterone levels should also be
monitored. The primary method of monitoring sex-steroid or antiandrogen therapy is direct measurement
of the relevant sex-steroids and gonadotropins. However, for many synthetic androgens and estrogens (eg,
ethinyl-estradiol) clinical assays are not available. In those instances, rises in SHBG levels indicate
successful anti-androgen or estrogen therapy, while falls indicate successful androgen treatment. Adult
SHBG levels in boys with signs of precocious puberty support that the condition is testosterone driven,
rather than representing premature adrenarche. Patients with anorexia nervosa have high SHBG levels.
With successful treatment, levels start to fall as nutritional status improves. Normalization of SHBG
precedes, and may be predictive of, future normalization of reproductive function. Thyrotoxicosis
increases SHBG levels. In situations when assessment of true functional thyroid status may be difficult
(eg, patients receiving amiodarone treatment, individuals with thyroid hormone transport-protein
abnormalities, patients with suspected thyroid hormone resistance or suspected inappropriate
thyroid-stimulating hormone (TSH) secretion such as a TSH-secreting pituitary adenoma), an elevated
SHBG level suggests tissue thyrotoxicosis, while a normal level indicates euthyroidism or
near-euthyroidism. In patients with gradual worsening of thyrotoxicosis (eg, toxic nodular goiter), serial
SHBG measurement, in addition to clinical assessment, thyroid hormone, and TSH measurement, may
assist in the timing of treatment decisions. Similarly, SHBG measurement may be of value in fine-tuning
suppressive TSH therapy for patients with nodular thyroid disease or treated thyroid cancer. Results are
not definitive in the short-term in patients receiving drugs that displace total thyroxine (T4) from albumin.
SHBG is also produced by placental tissue and therefore values will be elevated during pregnancy.
Current as of January 4, 2013 7:15 pm CST 800-533-1710 or 507-266-5700 or MayoMedicalLaboratories.com Page 1587