Regulating electrolyte balance is a major function of the kidneys. In normally functioning kidneys, urine levels increase when serum levels are high and decrease when serum levels are low to maintain homeostasis. Analyzing urinary electrolyte levels can provide important clues to the functioning of the kidneys and other major organs. Tests for calcium in urine usually involve timed urine collections during a 12- or 24-hr period. Measurement of random specimens may also be requested. Urinary calcium excretion may also be expressed as calcium-to-creatinine ratio: In a healthy individual with constant muscle mass, the ratio is less than 0.14.