A-068 The Chill Factor: Is Rigorous Specimen Handling Essential for Adrenocorticotropic Hormone Testing?

Abstract Background Adrenocorticotropic hormone (ACTH) is known to be unstable and prone to proteolytic degradation. This necessitates the need for rigorous specimen handling procedures involving the use of pre-chilled EDTA tubes and refrigerated centrifugation. As a result, ACTH collections are restricted to facilities with refrigerated centrifuges that may not be widely available in many rural areas, further limiting testing availability and creating a burden for physicians, patients, and laboratory staff. The purpose of this study was to investigate the effect of temperature during ACTH specimen handling and determine optimal plasma stability limits. Methods Specimens were collected from volunteers (N=21) and patients with Cushing’s-related disorders who have elevated ACTH above the upper reference limit of 14 pmol/L (N=5). The default specimen handling protocol involving pre-chilled EDTA tubes, transport on ice, and refrigerated centrifugation was compared against processing only at room temperature (RT). After centrifugation, ACTH was measured on the Roche Cobas e801 and Siemens Immulite immunoassays. Plasma stability was evaluated at RT, 4°C degrees, and -20°C across 24-72 hours. Mean difference between control and experimental groups were calculated against a state-of-the-art derived acceptable change limit (ACL) of 2 pmol/L for results <14 pmol/L or 26% for results =14 pmol/L. Results Differences (90th confidence intervals) on Roche between non-chilled tubes and RT centrifugation in volunteers were -0.2 pmol/L (-0.35, -0.051) and patients were -3.7% (-6.6, -0.83). The differences on Immulite in volunteers were -0.035 pmol/L (-0.27, 0.20). None of the differences exceeded the ACL. Plasma stability studies found ACTH remained stable at 4°C up to 48 hours and -20°C up to 30 days. Significant degradation was observed at RT at 24 hours. No degradation was observed after 2 freeze thaw cycles or thawing frozen plasma at RT for 2 hours. Conclusion ACTH was unaffected by non-chilled tubes and RT centrifugation on Roche and Immulite assays. Plasma is more stable when frozen. This was confirmed across a wide range of ACTH results relevant to patients. Elimination of rigorous specimen handling for ACTH will simplify collection requirements and enable better access to testing across an extended range of collection sites. Optimization of stability limits will also help laboratories define acceptable delay times and storage conditions.