Plasma renin activity refers to how active a specific enzyme, called renin, is in the liquid part of the blood. This enzyme is important in several of the body's systems, and is particularly crucial for regulating blood pressure. A plasma renin activity test, or assay, can be used to measure the activity of this enzyme. Abnormal test results can be an indicator of heart, kidney, or liver disease, as well as certain types of cancer. High renin activity can also cause hypertension.
Renin is produced by specialized cells in the kidneys. It is made when the body's levels of sodium are low, or when blood volume is reduced, such as by an injury or hemorrhage. In addition, renin triggers the production of a hormone called aldosterone, which is involved in biochemical pathways that regulate salt and water balance in the body. The various roles mean that this enzyme is highly influential in regulating the body's blood pressure.
Blood pressure regulation occurs via the renin-angiotensin system, also known as RAS. This system involves not only renin and aldosterone, but also several other proteins, including angiotensin and a corresponding enzyme, angiotensinogenase. The kidneys release renin when blood pressure drops, and the enzyme then acts on angiotensin to cause blood vessel constriction. Renin also stimulates the production of aldosterone, and these two factors cause blood pressure to increase and blood levels of sodium and potassium to stabilize.
Plasma renin activity is measured via a venous blood test, meaning that blood is drawn from a vein and tested for renin levels and activity. The test is conducted by assessing the rate at which the enzyme in the blood sample reacts with synthetic angiotensin. This test is typically carried out to help diagnose and treat hypertension, as the results of the test influence the type of medication most appropriate for an individual patient. In addition, this test might be ordered as part of the diagnostic process for diseases such as Conn's syndrome and Addison's disease.
In addition to its role as a diagnostic marker for hypertension, plasma renin activity is increasingly used as a predictive marker for cardiovascular events such as heart attacks. According to the results of long-term heart health study called the Heart Outcomes Prevention Evaluation Study, people with elevated baseline plasma renin activity levels have an increased risk of heart failure and death due to cardiovascular events. Identifying these types of markers is important because it helps identify who is at risk, as well as the best types of treatment for them.