Myeloperoxidase (MPO) has been shown to be potential risk marker for atherosclerosis. Biochemically belonging to the haem peroxidase superfamily, MPO is the most abundant constituent of the azurophilic granules of polymorphonuclear leucocytes (neutrophils, monocytes and some of tissue macrophages). MPO amplifies the oxidative potential of its cosubstrate hydrogen peroxidase, which then generates hypochlorous acid and other oxygen radicals with bactericidal and viricidal properties. When secreted into the extracellular space, MPO appears to be responsible for converting LDL cholesterol to its oxidised form, which then attaches itself to the endothelial plaques of coronary arteries.
US studies involving the measurement of MPO levels in 600 patients presenting with chest pain have shown that MPO measurement may be particular beneficial in such patients who have low initial troponin levels. MPO determination made it easier to identify patients who experienced a major adverse cardiac event in the period 30 days to six months after presentation. Without using MPO levels, only 54 % such cases could be identified where as with MPO 85 % were identified. Such studies have been confirmed in another European study. These studies suggest that when the MPO level is above a certain cut off value (350 ng/ml) there is a considerably increased risk of heart attack.
Principle Of The Test
The CD MPO test is based on immunochromatography. The reaction takes place in a nitrocellulose membrane. A MPO-specific monoclonal antibody has been applied to the membrane to form 2 test reaction zones. The other antibody is bound to coloured gold particles to form the label, which is applied on the filter.
MPO in the sample reacts with the label antibody. In the test zone the particles with MPO are captured by another anti-MPO-antibody and a coloured test line is formed. The rest of the particles will be captured by the second stationary antibody zone, thus forming the control line. A control line is always formed when the test is working properly.
Testing is performed by adding 3 drops (appr. 110μl) of diluted whole blood sample into the round sample well of the CD testing device. The sample flows through the membrane in 15 minutes. The result can then be read with the CD Quant reader unit. Intensity of the test line depends on the concentration of MPO in the sample.
Sensitivity and specificity of the test are high and false negative results due to an excess of MPO have not been demonstrated. The test devices and dilution buffers are stored at room temperature and have 18 months shelf life.