The aim of the study was to investigate the effect of different coagulants and storage conditions on the stability of ACTH in plasma using the LIAISON-ACTH-Chemiluminescence Immunoassay.
Design and methods: Sequential human blood samples were collected from healthy volunteers (n=83) between 8 and 10 pm into EDTA collection tubes (Sarstedt) and EDTA plus aprotinin tubes (Vacuette, Greiner Labortechnik), respectively. After collection the blood samples were centrifuged immediately at 4 °C and on the other hand a second aliquot at room temperature, then assayed for ACTH immediately and after storage times of 2, 4, 8, and 24 h at 4 °C and other aliquots at room temperature.
ACTH was determined using the fully automated LIAISON random access analyser.
Results: EDTA-plasma samples collected with aprotinin centrifuged and stored at 4 °C showed the best stability of ACTH until 8 h with 94.0% in comparison to the ACTH concentration immediately after centrifugation; on the other hand centrifuged at 22 °C and stored at 22 °C the ACTH was stable for 4 h with 92.0%. ACTH in plasma samples without aprotinin centrifuged and stored at 4 °C was stable until 8 h with 92.6%; the ACTH centrifuged at 22 °C and stored at 4 °C was stable until 2 h with 99.0%; the ACTH was unstable after centrifugation and storage at 22 °C with a decrease at 2 h to 88.8%.
Conclusion: ACTH in EDTA-plasma after centrifugation at 22 °C is stable at 4 °C only for 2 h, the stability is extended until 8 h after centrifugation at 4 °C. The addition of aprotinin showed an improvement of the stability especially at 22 °C.