Basal Measurement

Androgen

 In decreasing order of serum concentration, the androgens present in a woman of childbearing age are DHEA-S (95% of adrenal origin), DHEA, androstenedione, testosterone, and DHT. The medical-scientific community has long debated which androgens should be measured to evaluate hyperandrogenism and the analytical methodologies employed. A reasoned laboratory approach is to assay total testosterone before initiating any medical therapy that may interfere with circulating levels. The total testosterone assay should be accompanied by free testosterone because the latter has greater diagnostic sensitivity for hyperandrogenism. However, there are critical analytical considerations that may limit the reliability of this test. Methodologically, free testosterone can commonly be assayed by ELISA as long as the inter-assay imprecision assessed internally within the laboratory remains below 10% and appropriate reference intervals are established in non-hyperandrogenic women. Alternatively, more accurate LC-MS/MS-based assays are now considered the gold standard for steroid hormones measurement, although their use is restricted almost exclusively to clinical research in specialized laboratories. Compared to the free testosterone assay, some authors have proposed an approach based on SHBG with total testosterone. The ratio between total testosterone and SHBG indicates the amount of free hormone indirectly and is, therefore, a valuable tool to identify possible states of hyperandrogenism, especially when accurate dosages of free testosterone are not available. Epidemiological studies have shown that high levels of total testosterone and low levels of SHBG have a high positive predictive value for polycystic ovary syndrome, a condition also characterized by hyperandrogenism. In addition, reducing circulating SHBG can be considered a marker of insulin resistance to predict the onset of metabolic syndrome and gestational diabetes in women with PCOS. The significance of Δ4-androstenedione and DHEA-S dosage in hirsutism patients is still poorly understood. Δ4-androstenedione may be considered a pro-androgen; therefore, its circulating concentration may not reflect the biological actions of the active hormone.

Moreover, plasma levels fluctuate with the ovarian cycle, higher in the lutein phase. For these reasons, its diagnostic value in the diagnosis of hyperandrogenemia may be limited. On the other hand, Δ4-androstenedione binds with lower affinity to SHBG than testosterone and, therefore, may have more significant androgenic potential. Also, for DHEA-S, there is no clear evidence of the usefulness of this assay in identifying hyperandrogenism, except for the suspicion of androgen-secreting adrenal tumors, since circulating DHEA-S is predominantly of adrenal origin. In general, the finding of elevated values of at least one androgen indicates a disorder associated with androgen excess. The reference values of the main androgens in women are described in Table 1.

Table1. Main diagnostic laboratory test for secondary amenorrhea

Gonadotropin

Gonadotropin is essential to differentiate the various forms of hypogonadism; i.e., elevated FSH and LH levels (hyper gonadotropic hypogonadism, primary ovarian insufficiency) or reduced levels of FSH, LH, and estradiol (hypogonadotropic hypogonadism, hypothalamic-pituitary alteration). Although not diagnostic, an LH/FSH ratio greater than 2 is frequently found in PCOS. It should be noted that the reference values vary considerably depending on the woman’s age and, during productive life, and menstrual cycle phases. Physiologically, during menopause, there is a marked increase in FSH (Table 1). However, gonadotropin in amenorrhea should not be isolated due to their inherent variability but confirmed in subsequent measurements.

Estrogen

Estradiol represents the most common estrogen measured in clinical practice. It provides helpful information on hypogonadism, menstrual cycle alterations, and ovarian tumors. Also, in this case, the reference values vary according to the menstrual cycle and the woman’s age. In women of child bearing age, estradiol levels show a pre-ovulatory peak around day 12 and anticipate the pre-ovulatory peak of LH. Throughout the rest of the cycle, estradiol levels remain low. The use of serum estrone assay has limited clinical significance.

Progesterone

 Progesterone increases physiologically following ovulation. The serum dosage of progesterone in the lutein phase (21st day of the cycle) is used to confirm ovulation. In many cases, it is possible to have regular but anovulatory menstrual cycles, as in the case of PCOS, in which the finding of anovulation is one of the diagnostic criteria.

17-OH-progesterone, a progesterone derivative, does not have a precise biological role but is of particular diagnostic importance because its circulating concentration, both in basal conditions and after stimulation by synthetic ACTH, increases in cases of congenital adrenal hyperplasia and, in particular, 21α-hydroxylase deficiency. The 17-OH-progesterone assay is used in the etiological diagnosis of hirsutism to identify a 21α-hydroxylase deficiency.

Dynamic Investigations

 GnRH Testing The GnRH test is used in the differential diagnosis of amenorrhea to identify a possible pituitary defect. It is performed by intravenous administration of GnRH and serum LH and FSH measurement at basal and after 15, 30, 60, 90, and 120 minutes. There is no consensus on the interpretation of the test. Generally, a peak of at least three times baseline for LH and at least two times baseline for FSH is considered normal. Hypothalamic forms generally respond to the test, while in pituitary forms, the response is absent or reduced. In case of an absent or reduced response, it is necessary to repeat the test after a few days because pituitary cells not subjected to endogenous stimulation by GnRH may not be responsive to acute administration when the test is per formed. This test has sometimes been used in differential diagnoses between constitutional growth retardation with delayed puberty and hypogonadotropic hypogonadism; however, its diagnostic performance in this context is poor. Overall, the clinical use of this test is limited because there is no agreement on the interpretation of the response to GnRH stimulation and its diagnostic cut-off.

Clomiphene Test

Although rarely used in clinical practice, this test allows assessing the degree of impairment of hypothalamic- pituitary axis function in patients with anovulatory cycles or oligorrhea. Clomiphene competes with estrogens to bind their receptor. When clomiphene binds the receptor, it blocks the negative feedback induced physiologically by estrogen on GnRH and gonadotropin synthesis. The test is performed by administering clomiphene orally for 5 days starting on day 5 of the menstrual cycle and assaying FSH and LH on days 5, 7, and 10 of the cycle; progesterone is assayed on day 21 to document ovulation. In patients with normal hypothalamic- pituitary function, an increase of FSH and LH greater than 50% of baseline and restoration of ovulation is observed, pointing toward ovarian pathologies. Conversely, an absent response to clomiphene (no increase in FSH and LH after stimulation) indicates hypo thalamic-pituitary deficiency. A hypothalamic defect may be suspected if the response to clomiphene is absent, but the GnRH test is positive.

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مواضيع ذات صلة

urinalysis (UA)

Zika virus (ZIKV)

d-xylose absorption test (Xylose tolerance test)

wound culture and sensitivity (C&S)

white blood cell scan (WBC scan, Inflammatory scan)

white blood cell count and differential count (WBC and differential, Leukocyte count)

vitamin D (25-hydroxy vitamin D2 and D3 ; 1,25-dihydroxyvitamin D [1,25(OH)2 D])

Basal Hormone Measurements of Testis

vitamin B12 (Cyanocobalamin and methylmalonic acid [MMA])

virus testing

viral cultures

Laboratory Investigations of Pheochromocytoma and Paraganglioma