Decreased levels are most commonly due to inadequate protein intake, malabsorption, or liver damage. Creatinine is also a protein breakdown product. Its level is a reflection of the bodies muscle mass. Low levels are commonly seen in inadequate protein intake, liver disease, kidney damage or pregnancy. Elevated levels are generally reflective of kidney damage and need to be monitored very carefully.
Uric acid is the end product purine metabolism.
High levels are seen in gout, infections, high protein diets, and kidney disease. Therefore most of the phosphate in the body is found in the bones. But the phosphate level in the blood is very important for muscle and nerve function. Very low levels of phosphate in the blood can be associated with starvation or malnutrition and this can lead to muscle weakness. High levels in the blood are usually associated with kidney disease.