Inhibin A measurement is mainly used as an adjunctive test in the diagnosis of ovarian tumors when used in combination with inhibin B and in the monitoring of these patients.
Originally, inhibin was the name given to a component of serum found to inhibit the secretion of follicular hormone (FSH) from the pituitary gland. In recent years, protein inhibins have been characterized and specific immunological tests have been developed for both inhibin A and inhibin B. These hormones are members of the TGF-β (Transforming Growth Factor beta) family. Structurally, they consist of dimers of two dissimilar protein subunits. Subunit a is common in both inhibins. In women, inhibin A is largely produced by the dominant follicle/corpus luteum. Normally men do not produce measurable levels of inhibin A.
In young girls, concentrations of inhibin A increase as adolescence progresses. Therefore, measuring inhibin A may help determine gonad maturation and diagnose early puberty in girls. When women reach reproductive age, inhibin A levels change during the menstrual cycle. Inhibin A levels increase during the follicular phase reaching a peak during the luteal phase, with an intermediate peak in ovulation. In the initial phase of menopause, circulating inhibin levels begin to decline and reach postmenopausal women at low rates.
During pregnancy, the fetoplacental unit produces relatively large amounts of inhibin A. Evaluation of inhibin A concentration in relation to fetal gestational age is applied in prenatal screening for Down syndrome and in the prediction of preeclampsia.
Patients with certain ovarian tumors have elevated serum levels of inhibin A or/and inhibin B. In these patients, inhibin A levels may be increased 6 to 7 times above the reference value. Inhibin measurement is a complement to cancer antigen 125 (CA 125) as an indicator of ovarian cancer. The majority of studies for inhibin A and B as markers of ovarian cancer are limited to postmenopausal women, where levels for both proteins are usually very low. Measurement of inhibin A has limited utility as an indicator of ovarian cancer in pre-menopausal women, with circulating levels being higher throughout the menstrual cycle and therefore difficult to interpret.
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. The correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings, and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
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