This urine test assesses creatinine levels and can be helpful in diagnosing the health and functioning of the kidneys. Creatinine is a chemical waste product produced by muscle metabolism. Normal functioning kidneys filter creatinine and other waste products out of your blood to be removed from the body via urination. Increased creatinine levels in the blood may suggest kidney disease or other conditions that affect kidney function. Daily creatinine production is fairly constant except when there is massive injury to muscle. The kidneys excrete creatinine very efficiently and blood levels and daily urinary excretion of creatinine fluctuates very little in healthy normal people. Creatinine levels may be slightly lower during pregnancy.