What is a urine protein:creatinine ratio?
The urine protein:creatinine ratio is a simple test that measures how much protein is being lost through the kidneys, and determines if the loss poses a health risk for the pet. The test involves measuring the amount of protein and creatinine in a urine sample, and mathematically dividing the protein value by the creatinine value.
What is creatinine and why is it used in this test?
Creatinine is a by-product of muscle metabolism. Creatinine is excreted in urine at an approximately constant rate, which means it can be used as a standard for comparison for other substances excreted in the urine.
Is protein loss through the kidney always significant?
A small amount of protein loss through the kidneys may not be important if the kidneys are otherwise working well and producing concentrated urine. However, if the kidneys are in difficulty and are producing dilute urine, then even small amounts of urinary protein loss may be abnormal and should be investigated. Substantial protein loss through the kidneys is worrisome, because protein is a precious substance that is needed for the long-term well being of the pet, and is difficult to replace.,
Does all urinary protein come from the kidneys?
No. Protein is often present in the urine if there is inflammation or bleeding anywhere in the urinary system. Protein that comes from inflammation or bleeding is not as worrisome, because the underlying problem can usually be treated or corrected, which will stop the urinary protein loss. However, if there is no bleeding or inflammation in the urinary system, then protein in the urine may indicate the presence of a complex problem that may be difficult to diagnose and treat.
Can any urine sample be used to measure protein:creatinine ratio?
No. The protein:creatinine ratio should be performed only on urine that is free of blood and inflammation. A complete urinalysis and sediment evaluation (see handout “Urinalysis”) should be completed to determine if the sample is suitable for the protein: creatinine ratio test. The presence of blood and inflammation in urine may give a falsely high result for the protein:creatinine ratio, suggesting there is kidney disease when none is actually present.
When is the Protein:Creatinine ratio diagnostic for a kidney problem?
A protein:creatinine ratio greater that 1.0 on a “clean” urine sample indicates there is medically significant protein loss through the kidneys. A value between 1.0 and 3.0 represents relatively mild disease, while a value greater than 3.0 -5.0 indicates more serious disease is present in the kidneys. In advanced kidney disease, the ratio may be greater than 15.0.
Does an elevated Protein:Creatinine ratio explain the underlying problem?
No. The protein:creatinine ratio only helps to establish the fact that a problem exists. Further testing is usually required and may involve ultrasound of the kidney or possibly a kidney biopsy. Once a complete diagnosis is made, plans can be made to manage the disease as effectively as possible.
Margo S. Tant BSc, DVM, DVSc.
© Copyright 2004 Lifelearn Inc. Used with permission under license. December 9, 2011