Diagnostic methods for the measurement of human TNF-alpha in clinical laboratory

Measurement of Tumour Necrosis Factor alpha (TNF-α) in peripheral blood is a useful tool to assess inflammatory responses in a large range of diseases. One of the major challenges for cytokine analysis is the availability of a proper analytical tool with high specificity, accuracy, linearity, precision, stability, and analytical sensitivity. Although available immunoassays are usually robust and reproducible, it is also true that they are not interchangeable. Two ELISA, four flow cytometric bead array (CBA) and four Luminex immunoassays were compared. Correlation between different techniques was almost absent, while some immunoassays based on the same technique showed significant correlation. Among the ten different assays evaluated, just few of them complied with the pre-established acceptance validation criteria. Interestingly, sera and plasma collected from the same healthy donor had significant different reference values. Samples stability was maintained in serum up to one week at four degrees, while plasma was stable only when it was frozen. Since several anti-inflammatory treatments are based on biologics targeting TNF-α (anti-TNF-α antibodies), potential interference with the immunoassays was tested and resulted relevant. This study shows that although each immunoassay presents benefits and drawbacks, just few assays are suitable for the measurement of TNF-α in clinical laboratories, demonstrating that, so far, the measurement of TNF-α in human blood is still not yet harmonised. In addition, we found that false negative results caused by anti-TNF-α treatments should be carefully considered for results interpretation.