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Falsely Elevated Interleukin-6 (IL-6): The facts

The interleukin-6 (1L-6) is a multifunctional pleiotropic cytokine, and is also known as interferon-ß2 (IFN-ß2), 26 kDa protein, B-cell stimulatory factor-2 (BSF-2), hybridoma/ plasmacytoma growth factor, hepatocyte stimulating factor and macrophage-granulocyte inducing factor 2A (MGI-2A). IL-6 is released by a variety of cell types such as, T cells, B cells, monocytes, fibroblasts, vascular endothelial cells, cardiac myxomas, bladder cell carcinomas, myelomas, astrocytoma and glioblastomas. It has a major role in the mediation of inflammatory and immune response initiated by infection or injury.

IL-6 can be elevated with inflammation, infection, autoimmune disorders, cardiovascular diseases, and some cancers also. In few of the cases it has been associated with an increased risk of disease development or worsening prognosis. As the levels of IL-6 are associated with medical diagnosis, therapy, and prognosis, monitoring the fluctuation of its levels may reflect the progression or regression of diseases. Recent studies have also shown that since IL-6 is an important marker of inflammation, it can guide the clinicians in recognizing patients with severe COVID-19 early in the disease course.

Nowadays, remarkable advances in instrument technology have improved the analytical accuracy of test enormously. However, falsely elevated IL-6 levels are being reported mainly due to the pre-analytical errors (like blood collection tubes handling, specimen storage temperature and time, plasma or serum separation, centrifugal timing).

On one hand, half-life of IL-6 is relatively short, and on the other hand, various stimuli lead to the continuous secretion of cytokines by blood cells. Coagulation processes can also induce cytokine release, resulting falsely raised levels of IL-6 in vitro. With the storage temperature and time increased, the serum IL-6 levels are increased obviously. IL-6 is also released from blood cells in unseparated specimens. Few studies reported that EDTA and cold storage can maintain the stability of IL-6. Shockingly, the serum IL-6 levels can elevate, even hundreds of times, if serum or plasma is not separated timely or if cold chain is not maintained.

Based on the recent studies and my experience, there are various factors that impact the cytokine IL-6 levels. Improper sample handing (pre-analytic error) may result in false results. Separate serum or plasma (Heparin or EDTA) from contact with cells as soon as possible and maintenance of cold chain during storage and transportation of samples are highly recommended for accurate estimation of IL-6 level. In case of abnormally high result which cannot be correlated clinically, please repeat with fresh sample to rule out preanalytical error as it is a labile parameter.

Dr Prashant Goyal, 
Chief Pathologist & Director



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