Jokingly referred to as "the big pee" by kidney patients and others who take this test frequently, 24-hour urine analysis is a painless, noninvasive way of evaluating how much protein a patient is excreting in his urine. The 24-hour urinalysis provides very accurate information that helps doctors diagnose kidney disease and urological disorders.
Purpose
A 24-hour test measures all the protein that passes into the urine in a 24-hour period. Doctors order this test whenever they suspect that kidney disease might be an issue. Healthy kidneys prevent proteins from leaking into the urine. Abnormally high levels of protein in the urine are a red flag for kidney disease. A 24-hour test might be ordered if a patient has high serum creatinine levels or other evidence of kidney damage, such as out-of-range values on a dipstick test for urine protein.
Procedure
According to the National Institutes of Health, the 24-hour urine test is quite simple. The patient gets up in the morning and empties her bladder as usual into the toilet. This is zero time. Then for the next 24 hours, every time the patient urinates, she collects all her urine in a plastic jug provided by a pharmacist or medical provider. At the end of the 24 hours, the patient returns the jug back to the lab. The lab measures all the protein in the urine.
Interpretation
The NIH reports that the normal value of urine protein is less than 150 mg per day, or less than 10 mg per dL of urine. If the patient spills more than 3.0 g of protein in his urine, he is considered nephrotic. Nephrotic patients often retain water, particularly in their feet and under their eyes. This condition is called edema.
Compliance Issues
A 24-hour urine test may be the gold standard for urine protein, but it only is as accurate as the patient's ability to collect every drop of urine. Because of difficulties with patient compliance, more and more doctors have been measuring urine protein using a protein creatinine ratio rather than a 24-hour test. The protein creatinine ratio test is reasonably accurate and does not have problems associated with patient compliance.
Calcium Test
In addition to the 24-hour urine test for protein, there is also a 24-hour urine test for calcium. The collection procedures for these tests are identical. At the end of the 24-hour collection period, the lab measures all the calcium in the urine. According to Cigna, a serum calcium test is usually more helpful than a urine calcium test, so this test is not used very often.
