Serum creatinine is a lab test that is performed during diagnosis of kidney disease and as part of routine blood work. Normal creatinine levels are 0.5 to 1.2 milligrams per decilitre. High creatinine levels can be a sign of damage to the kidneys or to the muscle, or an effect of increased muscle mass.
Creatine phosphate is used in skeletal muscle contraction. Creatinine is a breakdown product of creatine. People with greater muscle mass produce a correspondingly greater amount of creatine and have higher levels of serum creatinine than smaller people or people with less muscle mass.
Because creatinine is excreted by the kidneys, its level in the blood is considered an indicator of kidney health. When the kidneys are functioning normally, the blood creatinine level is relatively constant day to day, though minor increases can occur after a high-protein meal.
Causes of Abnormal Creatinine
Increased blood creatinine is usually a sign of problems with kidney function. The creatinine level is also raised with injury to muscle and during increased breakdown of muscle tissue. Increases in muscle mass will also raise the level of serum creatinine. Conversely, decreased muscle mass will decrease blood creatinine.
Kidney Damage and Creatinine
Any disease that affects the filtration process of the kidneys will tend to raise serum creatinine levels over time. Doubling of serum creatinine levels is indicative of a 50 per cent reduction in the filtration rate of the kidneys. Diseases linked to increased creatinine levels include glomerulonephritis, pyelonephritis, diabetic nephropathy and conditions such as shock and congestive heart failure that reduce blood flow through the kidneys.
Muscle Damage and Creatinine
Muscle damage (rhabdomyolysis) releases a protein called myoglobin into the bloodstream. Large amounts of myoglobin are toxic to the kidneys so the serum creatinine levels rise. Rhabdomyolysis can result from trauma. It is also a side effect of certain drugs, including the statins.