The phosphorus test is used to monitor the levels of phosphorus in the blood. Most of the body’s phosphorus is in a form combined with calcium to help form bones and teeth, but it is also found in muscle, nerve tissue, and, in tiny but crucial amounts, within cells throughout the body, where it is a component of key molecules such as DNA. About 80% of phosphorus resides in the bones and teeth. Because alcohol can leach phosphorus from the bones, phosphorus deficiency is often associated with alcoholism, especially when combined with malnutrition.