Renin is an enzyme, or protein, that controls the body's blood pressure. It is made by the kidneys and can be measured to indicate a problem with the adrenal glands and their production of the hormone aldosterone. Usually, low renin levels correspond to high levels of aldosterone. Those with high aldosterone levels have a condition called hyperaldosteronism, which is a form of hypertension. Low renin levels therefore are associated with symptoms of hypertension, and may also correlate to low potassium in a condition known as Conn's syndrome.
Hyperaldosteronism is characterized by high blood pressure. Blood tests that indicate low renin levels are used to diagnose hyperaldosteronism. It is one of the forms of hypertension that does not usually get better with blood pressure medication. Some of the side effects of high blood pressure caused by hyperaldosteronism include a general weakness in major muscle groups, dizziness when standing, paralysis, headaches, tingling sensations in the limbs and general fatigue.
Sometimes, high blood pressure is caused by a constriction of the arteries. In individuals with hyperaldosteronism, low renin levels can result in artery constriction and thus higher blood pressure, while higher renin levels are associated with lower blood pressure. Renin has a direct effect on blood pressure and is secreted to keep it within normal ranges.
When a person's kidneys produce low renin levels, it can indicate that the adrenal glands might be producing too much aldosterone. The overproduction may be the result of a tumor. Symptoms may emerge due to the associated increase in blood pressure. The kidneys usually secrete more renin as a result of lower amounts of sodium in the bloodstream, a decrease in the amount of blood, or a high amount of potassium.
Low amounts of potassium in the bloodstream that are accompanied by hypertension can be another of the side effects of low renin. When renin is low and aldosterone levels are high, individuals are typically diagnosed with Conn's syndrome, which is considered to be a form of secondary hypertension. This condition can often be accompanied by low levels of potassium, which is also called hypokalemia.
Some of the symptoms or effects that occur with hypokalemia and hypertension are increased levels of urination and thirst. Individuals may notice heart palpitations, headaches and muscle cramps in addition to the symptoms associated with high blood pressure. Increasing salt intake usually aggravates the symptoms.
Causes of hyperaldosteronism are not necessarily related to renin levels. It is usually a problem with the person's adrenal glands. They may be overzealous or the person could have developed a mass, which in most cases is non-cancerous.