IDEXX VetTest® Chemistry Analyzer

What does the IDEXX Urine P:C Ratio measure?

The IDEXX Urine P:C Ratio measures urinary protein loss. It can detect very low levels of protein (›5 mg/dL) in canine and feline urine samples. By also measuring urine creatinine levels and forming a ratio of urine protein to urine creatinine, the IDEXX Urine P:C Ratio measures urinary protein loss while automatically correcting for variations in urine volume and concentration.

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Does an elevated Urine P:C Ratio indicate renal disease?

An elevated Urine P:C Ratio indicates that there is a clinically significant amount of protein in the urine. In order to determine if renal disease is responsible for this urinary protein loss, you must first localize the protein loss to the kidneys by ruling out prerenal and postrenal causes (via a history, PE, CBC, biochemical profile and a complete urinalysis). And because the test is so sensitive, you must rule out transient proteinuria (which can be caused by fever, exercise and changes in temperature) to determine that the proteinuria is persistent.

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What are the reference ranges for the individual urine chemistries—urine protein and urine creatinine?

We do not have reference ranges for urine protein and urine creatinine. The individual urine protein and urine creatinine results should not be evaluated on their own since the individual measurements (UPRO and UCRE) can change significantly within a short time frame, and are sensitive to urine volume and concentration. The benefit of the urine protein:creatinine ratio is that it automatically corrects for variations in urine volume and concentration.

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Is a negative result for protein on a urine dipstick insignificant?

Urine protein dipsticks are semi-quantitative and are influenced by urine pH, volume, concentration and color. While it is very easy to perform, the urine dipstick is neither a sensitive nor specific indicator of urinary protein loss. The lower limit of detection for urine protein on a dipstick is 30 mg/dL. The IDEXX Urine P:C Ratio has a lower limit for urine protein of 5 mg/dL, and is highly specific for dog and cat proteinuria. Furthermore, the IDEXX Urine P:C Ratio corrects for variations in urine concentration and volume. You should perform a Urine P:C Ratio on all suspect renal disease patients regardless of a negative urine protein dipstick result.

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At what age should dogs and cats be tested for early renal disease with an IDEXX Urine P:C Ratio?

Given the high prevalence of renal disease in geriatric dogs and cats, IDEXX recommends adding the Urine P:C Ratio to your senior care diagnostic protocol. We also recommend performing a Urine P:C Ratio on all animals suspected of having renal disease, regardless of age. Special attention should be given to breeds predisposed to renal disease, as well as all patients with diseases associated with secondary renal complications.

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After identifying a dog or cat that tests positive on the IDEXX Urine P:C Ratio, what is the next step?

As described in the diagnostic protocol, the first step is to localize the protein to the kidney by ruling out prerenal and postrenal causes of proteinuria. This is done by assessing the physical examination, complete urinalysis (including sediment exam), serum chemistry panel and complete blood count for evidence of underlying disease conditions that could be responsible for the proteinuria. The next step outlined in the diagnostic protocol is to rule out transient proteinuria by repeating the IDEXX Urine P:C Ratio. After both of these steps are completed, the diagnostic protocol aids in the evaluation of urinary protein loss.

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Why do I have to determine persistence?

Because the urine protein:creatinine ratio is so sensitive, it can detect very small amounts of protein in the urine that are of a transient nature. You have to rule out this transient, or functional proteinuria, which can be associated with increases in blood pressure as well as stress, exercise and fever, in order to determine that the protein is significant.

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Does the Urine P:C Ratio result correlate to patient prognosis?

Several studies have indicated a strong correlation between the UPC result and patient prognosis. The higher the urine protein:creatinine ratio, the worse the prognosis. Since the IDEXX Urine P:C Ratio is fully quantitative, the veterinarian can use this test not only to diagnose renal disease, but also as a prognostic indicator. Sequential Urine P:C Ratios can be used to monitor patient response to treatment and disease progression.

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Why do some dogs and cats with end-stage renal disease test negative for protein on the Urine P:C Ratio or have a result that actually decreases over time?

Dogs and cats with end-stage renal disease can potentially have a negative result with the Urine P:C Ratio. As the number of functional nephrons (the functional units of the kidney) decline, proteinuria may decrease or become negative. It is not uncommon to find a decreasing trend in the magnitude of Urine P:C Ratio as renal disease progresses to a terminal state.

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Is kidney disease reversible?

At this time, it has not been proven that medical intervention can physiologically reverse nephron damage. However, by catching the disease in an early stage, the veterinarian has the ability to prevent further damage and arrest disease progression.

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Can I use the Urine P:C Ratio to monitor therapeutic response?

Yes. Because the Urine P:C Ratio is fully quantitative, it can be used to monitor therapy. In fact, recent studies have shown that persistently high urine protein:creatinine ratios are significantly correlated to a poor prognosis.

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Is the Urine P:C Ratio of benefit in dogs and cats that have evidence of a urinary tract infection?

In the majority of cases of postrenal disease, a urine protein:creatinine ratio offers little diagnostic benefit and may be misinterpreted as a false-positive result. The protein in postrenal disease is of cellular origin (RBC, WBC, bacteria, tumor cells, etc.), and is not indicative of glomerular disease. In this case, a high urine protein:creatinine ratio may result due to a high protein level without a corresponding high creatinine level. Glomerular function cannot be evaluated until the underlying postrenal disease is resolved. It is important to mention that pyelonephritis (bacterial infection of the kidneys) will also have bacteria in the urine and should be suspected in complicated UTI cases or whenever there is a UTI in a clinically ill patient.

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What is the difference between proteinuria and microalbuminuria?

Proteinuria refers to an excessive amount of protein detected in the urine. Urine protein can be a complex combination of components that may include albumin, globulins, immunoglobulin light chains and low molecular-weight proteins. Microalbuminuria refers to the measurement of small quantities of albumin in the urine. In other words, microalbuminuria alludes to a small urine albumin concentration, typically <30 mg/dL, that is undetectable by semi-quantitative dipstick tests.

The IDEXX Urine P:C Ratio measures all fractions of urine protein, including albumin. Different methodologies used for the urine protein measurement will have variable sensitivities to different protein fractions, especially the globulin fractions. However, almost all methodologies will detect the albumin fraction.

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Is it important to detect the other proteins in addition to the albumin?

Yes, it is important to detect the other proteins in addition to the albumin. In renal diseases, albumin can be the predominant protein; however, other urine protein fractions may also be present, and these concentrations can vary, depending on the underlying condition. Immunoglobulins and other proteins can have an impact on the urine protein results, depending on the nature of the underlying disease.

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For years, veterinarians have used the dipstick for detecting proteinuria. Isn't the dipstick good enough?

Unfortunately, many veterinarians today are depending on the urine protein dipstick dye test to determine proteinuria. This test is neither sensitive nor specific, and can often yield erroneous results.

"If you're interested in detecting a low level of protein in the urine, the dipstick is not sensitive enough. We're going to get a lot of false-positives, but we may also see some false-negatives with a low proteinuria level. The sulfosalicylic acid, urine microalbumin, and urine protein:creatinine ratio tests are much more sensitive than the dipstick at detecting these lower concentrations of protein in the urine." Dr. Gregory F. Grauer¹

Because of poor specificity of the dipstick as a screening tool, IDEXX Reference Laboratories routinely performs a confirmatory SSA with any urinalysis when a dipstick assay is positive for protein. The SSA test result is included in the urinalysis report.

"The standard dipstick tests for protein are of little help when screening cat urine because there are so many false-positives. There are two possible approaches: 1.) run a urine protein:creatinine ratio initially and forget the screening test, or 2.) screen with the microalbuminuria test."
Dr. Jonathon Elliott¹

Regardless of the screening test used, initial discovery of proteinuria requires localization, proof of persistence and tracking of trends via the UPC ratio.

"We mainly use serial urine protein:creatinine ratios to evaluate proteinuria magnitude because they are useful for measuring any level of proteinuria." Dr. George E. Lees¹

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How is proteinuria determined to be persistent?

Proteinuria can be transient and not associated with renal disease, therefore, it must be determined to be persistent. Persistent renal proteinuria in nonazotemic animals is a sign of early renal disease. After the urine protein is localized to the kidney and evidence of lower urinary tract disease is not identified, it must be determined to be persistent. Persistence in nonazotemic animals is determined by identifying proteinuria on three or more occasions at least two weeks apart. By detecting the damage to the kidneys before azotemia is present and the patient's urine concentration ability is impaired, the veterinarian can minimize disease progression and improve the patient's prognosis. If the animal is azotemic and proteinuric, and lower urinary tract disease is excluded, the proteinuria can be attributed to renal disease.

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