Sodium blood test is one of the tests in which the electrolytes in your body are checked. Sodium is an essential electrolyte present in your body fluid and is responsible for the neuro-muscular activities. It helps in the cell functioning of the body and also regulates the amount of fluid in the body. When you are suffering from symptoms that may cause illness in brain, lungs, heart, kidney or adrenal glands, then the doctor may prescribe for electrolyte or sodium test. In the condition of dehydration, edema or other symptoms like confusion, thirst or dry mucus, sodium test may be prescribed to know the real issue.