A new generation IRMA for ACTH with improved specificity: validation in various physiological and pathological conditions.
OBJECTIVE
Measurement of plasma ACTH is a key step for the exploration of hypothalamic-pituitary-adrenal disorders. To further improve ACTH recognition a new generation of ACTH IRMA was developed using antibodies directed towards succinylated ACTH (sACTH IRMA).


METHODS
The usefulness of this assay was compared with that of another commercially available ACTH IRMA assay using intact ACTH (ELSA-ACTH) in various pathophysiological situations: patients with low ACTH plasma levels, high ACTH plasma levels with normal or tumoural pituitaries, or ectopic ACTH syndrome, and pregnant women with high proopiomelanocortin (POMC) plasma levels.


METHODS
All plasma samples were assayed simultaneously with the two different IRMAs. Comparisons were assessed by plotting the results along the theoretical line of identical values, and by the graphical method of Bland and Altman.


RESULTS
In the ELSA-ACTH IRMA, CLIP (or ACTH18-39) showed true cross-reactivity, and alpha-melanocyte-stimulating hormone and purified POMC both interfered and induced falsely lower ACTH results; in the sACTH IRMA no peptide showed any cross-reactivity, and only extremely high values of CLIP (50 000 pg/ml) interfered and induced falsely lower ACTH results. In ACTH hypersecretory syndromes, of tumoural (Cushing's disease, ectopic ACTH secretion) or non-tumoural (Addison's disease, congenital adrenal hyperplasia) origins a good agreement between the two assays was observed except for very high ACTH plasma values (above 1000 pg/ml) and in some tumours where the sACTH IRMA yielded lower results; in some cases, the presence of circulating CLIP, demonstrated by HPLC studies, may contribute to this discrepancy. It is also likely that the calibration of the ELSA-ACTH kit itself generates higher ACTH values. In normal pregnant women both IRMAs gave highly correlated values, yet lower results were obtained with the sACTH IRMA.


CONCLUSIONS
These data show that the sACTH IRMA has improved qualities of specificity and usefulness for rapid assessment of ACTH plasma levels.
Guiban
D
D
Laboratoire d'Hormonologie, UPR CNRS 1524, Institut Cochin de Genetique Moleculaire (ICGM), Paris, France.
Massias
J F
JF
Dugué
M A
MA
Coste
J
J
Bertagna
X
X
Raffin-Sanson
M L
ML
D000182:ACTH Syndrome, Ectopic / Q000097:blood; D000236:Adenoma / Q000097:blood; D000324:Adrenocorticotropic Hormone / Q000097:blood*; D000328:Adult; D000918:Antibody Specificity; D002851:Chromatography, High Pressure Liquid; D003480:Cushing Syndrome / Q000097:blood; D004700:Endocrine System Diseases / Q000097:blood*; D005260:Female; D006801:Humans; D015592:Immunoradiometric Assay / Q000379:methods*; D010911:Pituitary Neoplasms / Q000097:blood; D011247:Pregnancy; D011333:Pro-Opiomelanocortin / Q000097:blood
D011333:Pro-Opiomelanocortin; D000324:Adrenocorticotropic Hormone