Endocrine Abstracts

Heterophilic antibodies are well-known interferent factors affecting most immunoassays. However, they have been poorly evaluated in routine clinical practice. Definition of Subclinical Cushing’s Syndrome (SCs) has been arbitrary and prevalence has shown significant variations related with the diversity of the diagnostic tests. In most of the guidelines a low or suppressed corticothropin (ACTH) level has been suggested as an important predictor of SCs. Here, we sought to investigate the burden of heterophilic antibody interference in ACTH immunoassays in SCs screening.

We designed a pilot study including all referred individuals (n=72) with incidentally discovered adrenal adenomas between June 2015 and January 2016. We identified seven individuals having disproportionally elevated ACTH levels (>15 pg/ml) despite non-suppressed 1 mg DST(>2.5 μg/dl). In four of the subjects, polyethylene glycol precipitation (PEG) showed decreased recovery suggesting a high molecular weight interfering substance.

Interference in immunoassays is a well-known but usually underestimated problem, leading to discordant results and unnecessary, time consuming, expensive additional tests. A simple method using PEG precipitation of ACTH samples could distinguish individuals with suppressed ACTH levels.