Paradoxical Results after Inadvertent Use of Cosyntropin [Adrenocorticotropin Hormone (1-24)] Rather than Acthrel (Ovine Corticotropin Releasing Hormone) during Inferior Petrosal Sinus Sampling.

Objective: The use of ovine corticotropin releasing hormone (oCRH) maximizes the diagnostic accuracy of inferior petrosal sinus sampling (IPSS) in patients with adrenocorticotropin hormone (ACTH)-dependent Cushing's syndrome (CS). oCRH is marketed as ACTHrel and, understandably, may be confused with cosyntropin [ACTH (1-24)]. The inadvertent substitution of synthetic ACTH(1-24) for oCRH (ACTHrel) during IPSS may cause unexpected and misleading results. The aim of this report is to raise awareness of the potential confounding results created when synthetic ACTH(1-24) is mistakenly used during IPSS.

Methods: We present 3 patients treated at 3 different centers with ACTH-dependent CS in whom ACTH(1-24) was mistakenly substituted for oCRH (ACTHrel) during IPSS.

Results: In all patients, there was an abrupt and unexpected decrease in plasma ACTH in the inferior petrosal sinus (IPS) samples after presumptive stimulation with oCRH. Re-evaluation of the patients' pharmacy records confirmed that synthetic ACTH(1-24) had been used rather than oCRH during each procedure. Because "sandwich" immunometric assays for ACTH measure the entire pool of endogenous ACTH, the administration of synthetic ACTH(1-24) artifactually decreases the endogenous plasma ACTH(1-39) measurement by binding only to the N-terminal antibody raised against ACTH(1-17) and not to the C-terminal antibody raised against ACTH(34-39). This results in a lack of a detectable sandwich complex and explains the apparent reduction in ACTH concentration.

Conclusion: An abrupt decrease in ACTH during IPSS suggests that synthetic ACTH(1-24) rather than oCRH (ACTHrel) has been administered. The labeling of oCRH as ACTHrel poses a potential patient safety problem about which endocrinologists, interventional radiologists, and pharmacists should be aware.