Another worthwhile lab test for people with kidney disease is the measurement of protein and urea nitrogen in a 24-hour urine collection. Measurement in a single urine sample is less informative, because it varies considerably from hour to hour. A 24-hour urine collection gives a much more precise estimate of just how much protein the kidneys are spilling and how much urea is being produced.
The 24-hour urea nitrogen excretion test is the best measure of how much protein you are eating, because almost all protein eaten is metabolized to urea. Various reports have appeared in which the reliability of "spot" urine samples is compared with 24-hour collections: Clearly the latter are preferable, even though they are much more trouble for the patient.
The technique of collecting the 24-hour sample is this: On awakening, the patient voids in the toilet as usual. From then on, all urine passed goes into a container, which is kept in the refrigerator, including the urine passed on awakening the following morning. It is important to remember to void in the container before having a bowel movement, because otherwise some urine may be lost. The completed collection can be kept in the refrigerator several days if necessary, but most patients collect it the day before their appointment with the doctor. If any urine is lost, you must start over; an incomplete collection is worse than none at all.
One problem that sometimes arises is finding a large enough container. Using more than one container for the 24-hour collection is problematic, because the lab must find a single large container to mix it all together, and sometimes it cannot to do this. Gallon plastic jugs are easy to come by, as milk and spring water are sold this way. A good rinsing with hot water is adequate. But some patients pass more than a gallon of urine a day as a result of problems with their kidneys' ability to conserve water. How does one locate a two-gallon container? The only answer I can give is to go and buy a big container of kitty litter, dump it out, and rinse it thoroughly. These plastic jugs can hold several gallons and have a handle.
From the 24-hour urea nitrogen excretion level, your doctor can calculate just how much protein you are eating, which will tell you how well you are following the diet.
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