Increased levels are determined by several factors. Prerenal causes occur as a result of reduced renal perfusion in dehydration, hypovolaemic states, or shock; severe muscle injury from burns, trauma, polymyositis, or rhabdomyolysis. Renal causes are infection, glomerulonephritis, or kidney failure with a consequent reduced GFR. Post-renal causes occur from renal stones which generate urinary obstruction.

Low creatinine levels occur as a result of low muscle mass, liver disease, significant fluid overload, and poor nutritional status, and are often seen in pregnancy.