Physicians often ask for urine samples collected over a 24-hour period, rather t

Here's an answer I found online: "Urine sample is taken to find out a number of things like sugar,protein,bacteria,creatinine,ketone bodies,w.b.c.,r.b.c.,puss cells etc,etc.but if a doctor recommends a 24 hour urine test,it means that besides other things he wants to assess the kidney function too.A single sample will only reveal the things as mentioned above."

Often the information needed for a diagnosis is the amount of a substance being lost per day and not simply its concentration in the urine. Because the amount of water present in the urine varies throughout the day, the only reliable way to estimate quantities per day is measure both average concentration (g/ml) and the total volume (ml/day). The product of these two quantities is the amount per day (g/day). An example of a clinical test that relies on analysis of a 24-hour urine is the creatinine clearance test, a measure of GFR.

I'll combine both ideas, thanks!