Stability of plasma adrenocorticotrophic hormone (ACTH): Influence of hemolysis, rapid chilling, time, and the addition of a maleimide

Objectives: The aim of this study was to examine the effects of hemolysis, rapid chilling, time, and the addition of a maleimide on the stability of human plasma ACTH measurements. Design and methods: Partially hemolyzed EDTA blood (n = 10), initially at 37 degrees C, was centrifuged at 4 degrees C either immediately or after rapid chilling in ice/water. Plasma ACTH was then measured either immediately, or after 1 h at 22 degrees C with or without the addition of 2 mM N-phenyl maleimide (NPM). Results: For 0.2% hemolysis compared to no hemolysis, the mean (+/- SEM) loss with immediate centrifugation and immediate ACTH measurement was 11 +/- 1%. This loss was significantly (p<0.002) reduced to 6 +/- 1% by an initial rapid chilling of the samples. For analysis after 1 h at 22 degrees C, the addition of NPM decreased the loss of ACTH from 15 +/- 2% to 2 +/- 2% (p<0.002). Conclusion: Rapid chilling, prompt analysis, and addition of NPM can each reduce the interference of hemolysis in the measurement of plasma ACTH concentrations. (C) 2010 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.