High creatinine levels are usually caused by impaired kidney function or kidney disease. In infants, high creatinine levels can be caused by bacteremia; high creatinine levels in adult males can be a sign of prostate cancer, according to MedicineNet.
Creatinine is produced by creatine, a molecule used for energy production in the muscles. Muscle mass in and the production of creatinine in the body remain fairly constant. The kidneys filter out and dispose most creatinine through urination. If kidneys become impaired in any way, the creatinine level in the blood rises since it is not being cleared properly by the kidneys, according to MedicineNet.