Low blood creatinine levels can be caused by a diet very low in protein, severe liver disease, a low muscle mass due to a disease or aging, or pregnancy, according to WebMD. Low creatinine clearance levels usually mean severe kidney disease but may also indicate liver or heart disease.
Blood creatinine levels are measured by a simple blood test, according to WebMD. Creatinine clearance tests are more complicated and report the amount of creatinine cleared from the blood via the urine. To calculate a creatinine clearance value, the volume of urine produced in 24 hours needs to measured, as does the urine and blood creatinine levels.