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°C, was centrifuged at 4°C either immediately or after rapid chilling in ice/water. Plasma ACTH was then measured either immediately, or after 1h at 22°C with or without the addition of 2mM 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 1h at 22°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.