| Creatinine is a product of muscle metabolism. It is produced at a nearly constant rate and is excreted in the urine. Because of its constant rate of production, the amount of creatinine in the urine is an indirect measurement of kidney function (glomerular filtration rate). If kidney function is significantly reduced, the urine creatinine will fall. With more severe degrees of kidney failure, the serum creatinine will eventually rise. A 24-hour collection of urine is the most accurate way to assess renal function with creatinine. A blood (serum) creatinine is also measured during this time and used to calculated the volume of urine needed to "clear" the measured amount of creatinine from the blood and into the urine. This is called the "creatinine clearance". Vigorous exercise or muscular trauma occurring during the collection will cause an increased amount of creatinine in the blood and may lead to false creatinine clearance results.
Serum proteins are normally extracted from urine prior to it being released from the kidney. Because the renal glomeruli are imperfect, normal individuals may occasionally have "trace" amounts of protein in their urine. Larger amounts (1+ or more) are considered abnormal and may reflect an underlying kidney problem. Urine protein can be measured on any urine sample (a "spot urine"), but the most accurate measure is with a 24-hour collection of urine. During pregnancy, due to the increased renal blood flow, some additional protein may be lost in the urine. This increased protein loss should not normally be in quantities exceeding 300 mg in 24 hours. If more than 300 mg in 24 hours is found, this may signal the development of pre-eclampsia. | 
