24 Hour Urine Collection

Once a year I am required to do an annual check up for kidney functions. Last month, I finally submitted a 24 hour urine collection, a lab work, sonogram and an x-ray. This month would be a mammogram, cardio, and a visit with my doctor. These are necessary to ensure that my transplanted kidneys are still working well. They want to make sure that I am not spilling a protein as well to check for the creatinine clearance.

This what wikipedia says about the 24 hours urine collection:

Renal function, in nephrology, is an indication of the state of the kidney and its role in renal physiology. Glomerular filtration rate (GFR) describes the flow rate of filtered fluid through the kidney. Creatinine clearance rate (C_Cr or CrCl) is the volume of blood plasma^[1] Both GFR and C_Cr may be accurately calculated by comparative measurements of substances in the blood and urine, or estimated by formulas using just a blood test result (eGFR and eC_Cr). that is cleared of creatinine per unit time and is a useful measure for approximating the GFR. Creatinine clearance exceeds GFR due to creatinine secretion which can be blocked by cimetidine. Alternatively, over estimation by older serum creatinine methods resulted in an under-estimation of creatinine clearance which provided a less biased estimate of GFR.

The results of these tests are important in assessing the excretory function of the kidneys. For example, grading of chronic renal insufficiency and dosage of drugs that are primarily excreted via urine are based on GFR (or creatinine clearance).

It is commonly believed to be the amount of liquid filtered out of the blood that gets processed by the kidneys. Physiologically, these quantities (volumetric blood flow and mass removal) are only related loosely.