Total testosterone levels because of the
depression of SHBG levels that occurs concomitant with increasing androgen
effects on the liver. Therefore, when moderate hyperandrogenism, characteristic
of many functional hyperandrogenic states, occurs, elevations in total
testosterone levels may remain within the normal range, and only free
testosterone levels will reveal the hyperandrogenism. Severe hyperandrogenism,
as occurs in virilization and that result from neoplastic production of
testosterone, is reliably detected by measures of total testosterone. Therefore, in practical clinical evaluation of
the hyperandrogenic patient, determination of the total testosterone level in
concert with clinical assessment is frequently sufficient for diagnosis and
management. When more precise delineation of the degree of hyperandrogenism is
desired, measurement or estimation of free testosterone levels can be
undertaken and will more reliably reflect increases in testosterone production.
These measurements are not necessary in evaluating the majority of patients,
but they are common in clinical research studies and may be useful in some
clinical settings. Because many
practitioners measure some form of testosterone level, they should understand
the methods used and their accuracy. Although equilibrium dialysis is the gold
standard for measuring free testosterone, it is expensive, complex, and usually
limited to research settings, in a clinical setting; free testosterone levels
can be estimated by assessment of testosterone binding to albumin and SHBG. Testosterone
that is nonspecifically bound to albumin (AT), is linearly related to free
testosterone (FT) by the equation:
AT=Ka [A] x FT,
Where AT is the albumin-bound
testosterone, Ka is the association constant of albumin for
testosterone, and [A] is the albumin concentration.
In many cases of hirsutism, albumin
levels are within a narrow physiologic range and thus do not significantly
affect the free testosterone concentration.
When physiologic albumin levels are
present, the free testosterone level can be estimated by measuring the total
testosterone and SHBG.
In individuals with normal albumin levels,
this method has reliable results compared with those of equilibrium dialysis.
It provides a rapid, simple, and accurate determination of the total and
calculated free testosterone level and the concentration of SHBG. The
bioavailable testosterone level is based on the relationship of albumin and
free testosterone and incorporates the actual albumin level with the total
testosterone and SHBG. This combination of total testosterone, SHBG, and
albumin level measurements can be applied to derive a more accurate estimate of
available bioactive testosterone and thus the androgen effects derived from
testosterone. Bioactive testosterone
determined in this manner provides a superior estimate of the effective
androgen effect derived from testosterone. Pregnancy can alter the accuracy of
measurements of bioavailable testosterone. During pregnancy, estradiol, which
shares with testosterone a high affinity for SHBG, occupies a large proportion
of SHBG binding sites, so that measurement of SHBG levels can overestimate the
binding capacity of SHBG for testosterone. Derived estimates of free testosterone, as
opposed to direct measure by equilibrium dialysis, are therefore inaccurate
during pregnancy. Testosterone measurements in pregnancy are primarily of
interest when autonomous secretion by tumor or luteoma is in question, and for
these, total testosterone determinations provide sufficient information for
diagnosis. For testosterone to exert its biologic effects on target tissues, it
must be converted into its active metabolite, DHT, by 5a-reductase (a cytosolic enzyme that
reduces testosterone and androstenedione). Two isozymes of 5a-reductase
exist; type 1, which predominates in the skin, and type 2, or acidic 5a-reductase,
which is found in the liver, prostate, seminal vesicles, and genital skin. The type 2 isozyme has a 20-fold higher
affinity for testosterone than type 1. Both type 1 and 2 deficiencies in males
result in ambiguous genitalia, and both isozymes may play a role in androgen
effects on hair growth. vDihydrotestosterone is more potent than testosterone,
primarily because of its higher affinity and slower dissociation from the
androgen receptor. Although DHT is the key intracellular mediator of most
androgen effects, measurements of circulating levels are not clinically useful.
The relative androgenicity of androgens is as follows:
DHT=300
Testosterone=100
Androstenedione=10
DHEAS=5.
Until adrenarche, androgen levels remain
low.
Around 8 years of age, adrenarche is heralded
by a marked increase in DHEA and DHEAS. The half-life of free DHEA is extremely
short (about 30 minutes) but extends to several hours if DHEA is sulfated. Although no clear role is identified for
DHEAS, it is associated with stress and levels decline steadily throughout
adult life. After menopause, ovarian estrogen secretion ceases, and DHEAS
levels continue to decline, whereas testosterone levels are maintained or may
even increase.
Although postmenopausal ovarian steroidogenesis
contributes to testosterone production, testosterone levels retain diurnal
variation, reflecting an ongoing and important adrenal contribution. Peripheral
aromatization of androgens to estrogens increases with age, but because small
fractions (2% to 10%) of androgens are metabolized in this fashion, such
conversion is rarely of clinical significance.
Laboratory Evaluation
The 2008 Endocrine Society Clinical
Practice Guidelines suggest testing for elevated androgen levels in women with moderate
(Ferriman-Gallwey hirsutism score 9 or greater) or severe hirsutism or
hirsutism of any degree when it is sudden in onset, rapidly progressive, or
associated with other abnormalities such as menstrual dysfunction, infertility,
significant acne, obesity, or clitoromegaly. These guidelines suggest against
testing for elevated androgen levels in women with isolated mild hirsutism
because the likelihood or identifying a medical disorder that would change
management or outcome is estremely low.
Medications that cause hirsutism are listed
and should be considered When laboratory testing for the assessment of
hirsutism is indicated, either a bioavailable testosterone level (includes a
total testosterone, SHBG, and albumin level) or a calculated free testosterone
level (if albumin levels are assumed to be normal) provides the most accurate
assessment of the androgen effect derived from testosterone. In clinical
situations requiring a testosterone evaluation, the addition of 17-hydroxyprogesterone
will screen for adult onset adrenal hyperplasia, when indicated . When
hirsutism is accompanied by absent or abnormal menstrual periods, assessment of
prolactin and thyroid-stimulating hormone (TSH) values are required to diagnose
an ovulatory disorder. Hypothyroidism and hyperprolavrinemia may result in
reduced levels of SHBG and may increase the fraction of unbound testosterone
levels, occasionally resulting in hirsutism. In cases of suspected Cushing
syndrome, patients should undergo screening with a 24-hour urinary cortisol
(most sensitive and specific) assessment or an overnight dexamethasone
suppression test. For this test, the patient takes 1 mg of dexamethasone at 11
p.m, and a blood cortisol assessment is performed at 8 a.m. the next day.
Cortisol levels of 2μg/dL or higher
after overnight dexamethasone suppression require a further workup for
evaluation of Cushing syndrome. Elevated 17-hydroxyprogesterone (17-OHP) levels
identify patients who may have AOAH, found in 1% to 5% of hirsute women. The
17-OHP levels can vary significantly within the menstrual cycle, increasing in
the periovulatory period and luteal phase, and may be modestly elevated in
PCOS. Standardized testing requires early morning testing during the follicular
phase.
According to the Endocrine Society
clinical guideline, patients with morning follicular phase 17-OHP levels of
less than 300 ng/dL (10 nmol/L) are likely unaffected .When levels are greater
than 300 ng/dL but less than 10,000 ng/dL (300 nmol/L), ACTH testing should be
performed to distinguish between PCOS and AOAH. Levels greater than 10,000
ng/dL (300 nmol/L) are virtually diagnostic of congenital adrenal hyperplasia.
Precocious pubarche precedes the
diagnosis of adult onset congenital adrenal hyperplasia in 5% to 20% of cases.
Measurement of 17-OHP should be performed in patients presenting with
precocious pubarche, and a subsequent ACTH stimulation test is recommended if
basal 17-OHP is greater than 200 ng/dL. A study using a 200 ng/dL threshold for
basal 17-OHP plasma levels to prompt ACTH stimulation testing offered 100% (95
% confidence interval [CI], 69-100) sensitivity and 99% (95% CI, 96-100)
specificity for the diagnosis of adult onset congenital adrenal hyperplasia
within the cohort with precocious puberty .
Because increased testosterone
production is not reliably reflected by total testosterone levels, the
clinician may chose to rely on typical male pattern hirsutism as confirmation
of its presence, or may elect measures that reflect levels of free or unbound
testosterone (bioavailable or calculated free testosterone levels). Total
testosterone does serve as a reliable marker for testosterone-producing
neoplasms. Total testosterone levels greater than 200 ng/dL should prompt a workup
for ovarian or adrenal tumors.
Although the ovary is the principal
source of androgen excess in most of PCOS patients, 20% to 30% of patients with
PCOS will demonstrate supranormal levels of DHEAS. Measuring circulating levels
of DHEAS has limited diagnostic value, and overinterpretation of DHEAS levels
should be avoided .
In the past, testing for androgen
conjugates (e.g.,3a-androstenediol G [3a-diol G] and androsterone G [AOG] as
markers for 5a-reductase activity in the skin) was advocated.
