An acute phase reactant is one of a series of special proteins that are created and secreted by the liver during illness, specifically during the inflammatory phase. There are an entire series of acute phase reactants and they are divided into positive acute phase proteins and negative acute phase reactants. The positive acute phase reactants are those that are secreted during inflammation whereas the others are secreted during normal function. We tend to think of the body's immune system as a series of signals that trigger the white blood cells to kill and clean off invaders; however, immunology is more complex than that. There are an entire series of proteins that aid in destroying pathogens by various processes that they affect. It is curious to note that since all of these proteins are created in the liver, the acute phase reactants test is also used to check for proper liver function.
The test is conducted primarily to check for the presence of inflammation in the body but is also used to check for any liver problems. This is because the proteins that are created during a bout of inflammation are created in the liver. Elevated acute phase reactants in the blood are usually a sign of the liver being in a state of battle. The absence of any kind of pathogen in the body can then mean that the liver is secreting enzymes that could literally destroy the body.
You must not be on any anti-inflammatory drugs like NSAIDS or corticosteroids before taking the test. You must also not be on any kind of antihistamines, as this could skew the results. Additionally, you should not be on birth control pills that are progesterone based either.
The test is a blood test that tests for levels of acute phase proteins and the test is also combined with an erythrocyte sedimentation test to judge the level of inflammation. The proteins that are secreted by the liver include enzymes like elastase. This destroys cellular tissue that is made of elastin and can be a serious cause of concern since the lung tissue is almost completely made of elastin. Other proteins reduce the availability of free iron in the tissues as a method of reducing the availability of iron to any pathogen. One of the most important proteins is called C-reactive protein. This protein will bind to a damaged cell or pathogen causing macrophages to identify the aberration in the body and then destroy it.