Stability of Tumor Necrosis Factor Alpha, Interleukin 6, and Interleukin 8 in Blood Samples of Patients with Systemic Immune Activation

Context: Tumor necrosis factor alpha, interleukin 6, and interleukin 8 serum/plasma levels are frequently used for the monitoring of patients with systemic immune activation/ sepsis. This requires comparability of test results over time. However, cytokines are usually not considered to be very stable after blood collection, which might artificially interfere with test results.

Objective: To obtain better knowledge about stability of these cytokines in blood samples for interpretation of test results.

Design: Blood of patients with systemic immune activation was collected in EDTA, lithium heparin, ammonium heparin, and serum tubes. Aliquots were analyzed after storage at room temperature for 2 to 8 hours. Additionally, storage conditions for separated serum/plasma for 24 hours and the reproducibility of repeated cytokine measurements by an automated DPC Immulite analyzer were tested.

Results: Tumor necrosis factor alpha level was stable in EDTA plasma for 8 hours, while slightly increasing in heparin plasma and serum. Interleukin 6 concentrations were stable for 8 hours in all blood types, whereas interleukin 8 concentrations were stable only in EDTA plasma and were strongly increasing in heparin plasma and serum. Cytokine concentrations in separated serum/plasma were stable during 24 hours if stored at 4 degrees C or frozen at -20 or -70 degrees C. Reproducibility of repeated cytokine measurements revealed no significant differences for all blood types.

Conclusions: Cytokine levels were most critically influenced by the period between blood collection and plasma separation, but its impact was strongly dependent on cytokine and anticoagulant. However, under appropriate conditions cytokine levels were surprisingly stable for up to 8 hours.