Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1015 page)

   Immunoassay (e.g., MEIA, EMIT, FPIA, RIA): FPIA demonstrates more cross-reactivity with cyclosporine metabolites than EMIT. Therefore, EMIT concentration may be 70% of FPIA concentration. Note that cross-reactivity of immunoassays may change over time, so consult the manufacturer’s package insert for current information.

   LC/MS concentrations are generally lower than immunoassay due to cross-reactivity of the immunoassay with metabolites.

INHIBINS A AND B, SERUM

   Definition

   Polypeptide hormones that belong to transforming growth factor family; these are secreted by granulosa cells of the ovary and Sertoli cells of the testis. Inhibit pituitary production of FSH. Secreted by the placenta during pregnancy. Inhibins are heterodimers and hence have two forms: alpha-beta A (inhibin A) and alpha-beta B (inhibin B).

   
Normal ranges:
see Tables 16.47 and 16.48.

TABLE 16–47. Normal Ranges for Inhibin A

TABLE 16–48. Normal Range for Inhibin B by Sex and Age

   Use

   
Females:

   Inhibin A is mostly produced by the corpus luteum.

   Undetectable before puberty.

   Very low levels in postmenopausal state due to absent follicular secretions.

   During pregnancy is secreted by the placenta. Inhibin A peaks at 8–10 weeks, declines until 20 weeks, and then increases gradually to term.