Evaluation of patients with suspected systemic infection
Evaluation of patients with suspected localized infection, specifically prosthetic joint infection (PJI)
1. Immediately after drawing the specimen, place the tube on wet ice.
2. Spin down and separate plasma from cells; 1,500 x g for 10 minutes.
3. Freeze specimen within 30 minutes
Interleukin-6 (IL-6) is a nonspecific marker associated with an inflammatory response and is not diagnostic for any specific disease or disease process. Elevated concentrations of IL-6 must be interpreted within the clinical context of the patient.
Normal concentrations of IL-6 do not exclude the possibility of an ongoing inflammatory process.
IL-6 has limited stability. Following centrifugation, plasma must be either immediately frozen or refrigerated. Specimens can be stored at refrigerated temperatures for only 24 hours, after which time they must be frozen. Storage of plasma for any length of time at ambient temperature is not acceptable.
Interleukin-6 (IL-6) has important roles in both innate and adaptive immunity.(1) IL-6 can be produced by a variety of different cell types, including macrophages, endothelial cells, and T cells. This production can be initiated in response to microbial invasion or other cytokines, such as tumor necrosis factor (TNF). As part of the innate immune system, IL-6 acts on hepatocytes to induce expression of C-reactive protein (CRP), fibrinogen, and serum amyloid A, also known as the acute phase response. Within the adaptive immune response, IL-6 plays a key role in activing antibody-producing B cells to proliferate, leading to an enhanced antibody response.
Concentrations of IL-6 are elevated in patients with infection, sepsis, and septicemia. In addition, IL-6 concentrations appear to correlate with severity of sepsis, as defined by clinical and laboratory parameters. Elevations in IL-6 also appear to be associated with more localized infections, such as prosthetic joint infections (PJI). A recent meta-analysis demonstrated that IL-6 had improved diagnostic accuracy for PJI compared to CRP, erythrocyte sedimentation rate (ESR), and white blood cell counts. IL-6 is also elevated in numerous chronic inflammatory disorders, including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), ankylosing spondylitis (AS), and inflammatory bowel disease (IBD). There is evidence that IL-6 is involved in the pathogenesis of certain chronic inflammatory disorders. Tocilizumab, an antibody that blocks IL-6 function by binding to the IL-6 receptor, has been approved for the treatment of RA. In a randomized trial, 50% to 60% of patients receiving tocilizumab and methotrexate showed improvement in clinical signs and symptoms of RA, compared to only 25% in patients receiving methotrexate alone.