Mayo Test Catalog, (Sorted By Test Name) - Mayo Medical ...

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. Reference ranges for pregnant females
have not been established in our institution. In patients with known insulin resistance, "metabolic
syndrome," or high risk of type 2 diabetes (eg, women with a history of gestational diabetes), low
SHBG levels may predict progressive insulin resistance, cardiovascular complications, and progression
to type 2 diabetes. An increase in SHBG levels may indicate successful therapeutic intervention. A
genetic variant of SHBG (Asp327->Asn) introduces an additional glycosylation site in 10% to 20% of
the population, resulting in significantly slower degradation. These individuals tend to have higher
SHBG levels for any given level of other factors influencing SHBG.
Reference Values:
Tanner Stages* Mean Age Reference Range (nmol/L)
Stage I 7.1 31-167
Stage II 11.5 49-179
Current as of January 3, 2013 2:22 pm CST 800-533-1710 or 507-266-5700 or MayoMedicalLaboratories.com Page 1595