A comparison of immunometric and radioimmunoassay measurement of ACTH for the differential diagnosis of Cushing's syndrome.
OBJECTIVE
Measurement of plasma ACTH levels by radioimmunoassay (RIA) is used to identify adrenal causes (AA) of Cushing's syndrome (CS) and to distinguish ectopic CS (EAS) from Cushing's disease (CD) using CRH stimulation testing and inferior petrosal sinus sampling (IPSS). We wished to determine whether diagnostic criteria developed with RIA would also be applicable for immunoradiometric (IRMA) or immunochemiluminescent (ICMA) assays.


METHODS
ACTH was measured by RIA, immunoradiometric and/or immunochemiluminescent assay on samples obtained during three types of diagnostic testing in a tertiary referral setting: a) basally (63 CD, 5 AA, 2 EAS and 37 non-CS patients); b) in 44 CD patients following CRH; c) in 6 ectopic CS and 17 CD patients during IPSS. The primary outcome was comparison of diagnostic utility.


RESULTS
a) IRMA results, while lower, correlated highly with RIA (r=0.9, p<0.0001) and had similar sensitivity (100 vs 80%) and specificity (89 vs 94%) for the diagnosis of AA (p=0.3); b) the sensitivity for CD of CRH testing using IRMA was similar to that of RIA (85 vs 83%, p=1.0); c) during IPSS, IRMA had similar sensitivity (100%) and specificity (100 vs 83%) compared with ICMA or RIA (p=1.0).


CONCLUSIONS
ACTH immunometric assays correlate closely to RIA and offer similar diagnostic utility.
Lindsay
J R
JR
Reproductive Biology and Medicine Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda MD 20892-1109, USA.
Shanmugam
V K
VK
Oldfield
E H
EH
Remaley
A T
AT
Nieman
L K
LK
D000324:Adrenocorticotropic Hormone / Q000097:blood*; D003346:Corticotropin-Releasing Hormone; D003480:Cushing Syndrome / Q000175:diagnosis*; D003937:Diagnosis, Differential; D006801:Humans; D007120:Immunochemistry; D015592:Immunoradiometric Assay / Q000379:methods*; D008163:Luminescent Measurements / Q000379:methods*; D047748:Pituitary ACTH Hypersecretion / Q000175:diagnosis*; D011863:Radioimmunoassay / Q000379:methods*; D012680:Sensitivity and Specificity
D000324:Adrenocorticotropic Hormone; D003346:Corticotropin-Releasing Hormone