A new generation IRMA for ACTH with improved specificity: validation in various physiological and pathological...

Area of Science:

• Endocrinology
• Immunoassay Development
• Clinical Chemistry

Background:

• Plasma adrenocorticotropic hormone (ACTH) measurement is crucial for diagnosing hypothalamic-pituitary-adrenal axis disorders.
• Existing ACTH immuno-radiometric assays (IRMAs) may exhibit cross-reactivity and interference, affecting diagnostic accuracy.
• A novel IRMA utilizing antibodies against succinylated ACTH (sACTH) was developed to enhance ACTH recognition.

Purpose of the Study:

• To evaluate the performance of a new sACTH IRMA assay.
• To compare the sACTH IRMA with a commercially available intact ACTH IRMA (ELSA-ACTH).
• To assess assay utility in various pathophysiological conditions affecting ACTH levels.

Main Methods:

• Simultaneous measurement of plasma samples using both sACTH IRMA and ELSA-ACTH.
• Comparison of results using Bland-Altman graphical analysis and theoretical line plotting.
• Evaluation in patient cohorts with low, high, and normal ACTH levels, including ectopic ACTH syndrome, pregnant women, and those with pituitary abnormalities.

Main Results:

• The sACTH IRMA demonstrated superior specificity, with no cross-reactivity from CLIP, alpha-MSH, or POMC, unlike the ELSA-ACTH.
• Both assays showed good agreement in ACTH hypersecretory syndromes, except at very high levels (>1000 pg/ml) or in specific tumors where sACTH IRMA yielded lower results, potentially due to circulating CLIP.
• While highly correlated in normal pregnancy, the sACTH IRMA consistently provided lower ACTH values compared to ELSA-ACTH.

Conclusions:

• The sACTH IRMA exhibits improved specificity and utility for rapid assessment of plasma ACTH levels.
• This new assay offers enhanced diagnostic potential for hypothalamic-pituitary-adrenal disorders.
• Further investigation into discrepancies at very high ACTH levels and in specific tumor types is warranted.