Acute phase reactants (APR) are inflammation markers that exhibit significant changes in serum concentration during inflammation. These are also important mediators produced in the liver during acute and chronic inflammatory states. Interleukin-6 (IL-6) is the primary cytokine responsible for inducing the production in the liver. IL-1, tumor necrosis factor-alpha (TNF-alpha), and interferon-gamma (IFN-gamma) can also induce the production of acute-phase reactants. Acute phase reactants cause several adverse effects. These include fever, anemia of chronic disease, anorexia, somnolence, lethargy, amyloidosis, and cachexia (fat and muscle loss, anorexia, weakness). Acute phase reactants can be classified as positive or negative, depending on their serum concentrations during inflammation. Positive acute phase reactants are upregulated, and their concentrations increase during inflammation. Negative acute phase reactants are downregulated, and their concentrations decrease during inflammation. Positive acute phase reactants include procalcitonin, C-reactive protein, ferritin, fibrinogen, hepcidin, and serum amyloid A. Negative acute phase reactants include albumin, prealbumin, transferrin, retinol-binding protein, and antithrombin.[1]