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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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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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