Calprotectin is a 36kDa calcium and zinc binding protein expressed by the gene S100 calcium-binding protein A8, S100A8. It accounts for 30 to 40% of neutrophils' cytosol. In vitro studies show it has bacteriostatic and fungistatic properties. It is resistant to enzymatic degradation, and can be easily measured in faeces.
 
Calprotectin is released by activation of leukocytes, giving increased levels in plasma, cerebral spinal fluid, synovial fluid, urine or stools as a consequence of disease in the relevant organ(s). Calprotectin inhibits zinc-dependent enzyme systems, as a result kills microbes and induces apoptosis in normal and cancer cells. In the presence of calcium, calprotectin is remarkably resistant to protelolytic degradation and so is stable in stools kept at room temperature for 7 days.
 
The Calprotectin Cassette employs red gold-conjugated monoclonal antibodies against human calprotectin, and solid-phase specific another calprotectin antibodies. In this test the specimen is first treated with an extraction solution to extract calprotectin from the faces. Following extraction, the only step required is to add the extract to the reaction device. As the sample flows through the test membrane, the colored particles migrate. In the case of a positive result the specific antibodies present on the membrane will capture the colored particles. Red color lines will be visible, depending upon the calprotectin content of the sample. These lines, after 5-15 minutes of incubation at room temperature, are used to interpret the result.