BLOOD TESTS TO DIAGNOSE OSTEOMYELITIS / BONE and SOFT TISSUE  INFECTIONS - 

The Erythrocyte Sedimentation Rate (ESR):   When inflammation is present in the body, proteins are produced by the liver and the immune system under many abnormal conditions, such as an infection, an autoimmune disease, and/or cancer.  The increased presence of these proteins will cause red blood cells to stick together in solution (whole blood) and, therefore, settle out of solution more slowly than when these proteins are absent or in lower concentrations.   The Erythrocyte Sedimentation Rate (ESR) is, therefore, a non-specific test to indicate thickening of the blood due and can be used to rule in or rule out disease processes that, when present, stimulate production of these proteins (see below discussion of acute phase proteins).   Since there are many possible causes of an elevated sedimentation rate, this blood test is done with other tests to confirm a diagnosis such as a chronic osteomyelitis.  Once a sed rate (ESR) blood test is conducted, the course of a disease or the effectiveness of treatment can be monitored.

C-reactive protein (CRP): CRP is believed to play another important role in innate immunity, as an early defense system against infection.  It is a protein found in the blood, the levels of which rise in response to inflammation due to trauma, infection or serious illnesses; it is an “acute-phase protein” synthesized by the liver.  It is not related to C-peptide or protein C.   A rise in C-RP is due to a rise in the plasma concentration of IL-6(see below), which is produced predominantly by macrophages and fat cells.   CRP binds to microbes and is thought to enhance the process of phagocytosis (cellular ingestion/digestion) of bacteria by macrophages.  

When signaled, the CRP level rises above normal limits within 6 hours, and peaks at 48 hours.  Thereafter, its level is determined by the rate of production (and hence the severity of the precipitating cause).  Measuring and charting C-reactive protein values can prove useful in determining the presence of disease, disease progress and/or the effectiveness of various treatments.

Acute-phase proteins:  a class of proteins whose plasma concentrations increase (positive acute-phase proteins) or decrease (negative acute-phase proteins) in response to inflammation. This response is called the acute-phase reaction (also called acute-phase response).  In response to injury, local inflammatory cells (neutrophils, granulocytes and macrophages) secrete a number of cytokines; cytokines are chemical signals between cells that have an effect on other cells, the most most notable of which are the interleukins IL-1, IL-6 and IL-8 and tumor-necrosis factor alpha (TNF- α).   

Interleukin-6 (IL-6) is both a pro-inflammatory and anti-inflammatory cytokine.  It is secreted by T-cells and macrophages to stimulate immune response to trauma, especially burns or other tissue damage leading to inflammation. IL-6 has been shown to be required for resistance against certain bacteria (i.e.; Streptococcus pneumoniae).  IL-6, one of the most important mediators of fever and of the acute phase response, can be secreted in response to specific microbial molecules referred to as pathogen associated molecular patterns (PAMPs).  These PAMPs bind to highly important group of detection molecules of the innate immune system called pattern recognition receptors (PRRs) which signal cascades giving rise to inflammatory cytokine production.

 At our Osteomyelitis Treatment Center in Sand Diego, CA we use the ESR, CRP and IL-6 blood tests in the diagnosis of bone and soft tissue infections as well as in the follow up following treatment results and peri-prosthetic total joint infections.