High levels of urine protein are a red flag for kidney disease. However, there are many different ways that urine protein can be measured, each with its own scale of values and method of collection. The protein-to-creatinine ratio is one of the more reliable ways of measuring urine protein. This technique is becoming more and more universal.
Preferred Methodology
The National Kidney Foundation recommends that nephrologists use either a protein-to-creatinine ratio test or an albumen-to-creatinine ratio when measuring urine protein. These tests overcome problems inherent in other measuring techniques, such as the 24-hour test, which requires strict patient compliance, and the dipstick test, which is inaccurate. The albumen-to-creatinine ratio test is very similar to the protein-to-creatinine ratio test. The only difference is that it focuses upon a specific protein rather than total protein count.
The dipstick test continues to be used as a screening tool because it is inexpensive and produces very few false positives. However, it is not an accurate way to measure total urine protein.
Collection and Calculation
The protein-to-creatinine ratio requires a single urine specimen. Some doctors require that the specimen be from the first urine of the day. Other doctors believe the test can use any urine specimen regardless of when it is obtained. The National Kidney Foundation states that "first morning specimens are preferred, but random specimens are acceptable if first morning specimens are not available."
The protein-to-creatinine ratio is a calculated value. The amount of urine protein and creatinine in a single specimen is measured in the lab. Each value is expressed in milligrams per deciliter. The amount of creatinine is divided by the amount of protein.
Relative Values
This test is more accurate than the dipstick test because it compensates for the variation in the amount of protein in the urine caused by the relative concentration of the urine. Urine protein can go up and down depending upon how much fluid you drink. This test compensates for this variation by creating a ratio from two variable numbers. Although those numbers may vary, the relationship between them remains constant.
Normal Values
Normal protein-to-creatinine ratio values depend upon the size of the person. The normal ratio for chidren under two years is less than 0.5. The normal ratio for adults and children over two years is less than 0.2. People who are nephrotic have protein-to-creatinine ratios of over 3.5.
