Comparison of Two Automated Adrenocorticotropic Hormone Assays

The measurement of adrenocorticotropic hormone (ACTH 1-39; M r 4500) plays a key role in the evaluation of hyper- and hypocortisolism (1)(2)(3), but low ACTH concentrations make accurate measurement challenging. Two automated, nonisotopic ACTH assays have become available in recent years. Because it is usual for rather small series to be assayed for ACTH in a clinical setting and because nonisotopic methods with stable calibration are of great practical interest, we compared these assays.Both assays investigated were solid-phase, sandwich immunoassays that use chemiluminescence for signal generation and are implemented on benchtop, multichannel, random-access analyzers with ready-to-use reagents.The Nichols Advantage ACTH assay (Nichols Institute Diagnostics) uses one acridinium ester-labeled mouse monoclonal antibody that specifically binds to the C-terminal region of ACTH and one biotin-labeled goat polyclonal antibody that binds to the N-terminal region. The sample is incubated for 21 min at 37 °C with both antibodies simultaneously, leading to the formation of a soluble sandwich complex in the presence of ACTH molecules. Streptavidin-coated magnetic particles are then added, and the reaction mixture is incubated for 10 min, during which the sandwich complex binds to the particles by biotin-avidin interaction. The particles are fixed to the wall of the single-use reaction cell magnetically, and unbound, labeled antibody is separated by aspiration and subsequent washing. Finally, two trigger solutions are injected into the reaction cells to initiate the chemiluminescent reaction, and the light emission is quantified over 2 s by a luminometer. A lot-specific master calibration curve is loaded by barcode and adjusted weekly with two calibrators by the user. The reported measuring range extends to 1500 ng/L. Barcode-labeled sample tubes are processed directly. The sample throughput is ∼90/h, and the time to first result is 37 min with a start-up time of ∼15 min.In the …