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Comparison of Methods Used for Determining Urine
Protein-to-Creatinine Ratio in Dogs and Cats.
The urine protein-to-creatinine (UPC) ratio is a cornerstone for
quantitative assessment of persistent proteinuria in dogs and cats.
Since there are no collectively accepted reference methods,
interlaboratory comparison of UPC ration are complicated by the variety of
assay methodologies used for measuring urine protein and urine
creatinine concentrations.
The purpose of this study was to evaluate common methodologies used
for the measurement of urine protein and urine creatinine
concentrations. Urine samples were collected from 21 dogs and 48 cats;
and for each sample, urine protein and urine creatinine concentrations
were measured using the VITROS® 250 chemistry system and Hitachi® 717
automated analyzer. Urine protein methods compared included a
colorimetric pyrocatechol violet dye-binding assay (UPRO dry slide,
Ortho-Clinical Diagnostics, Rochester NY) and a turbidimetric
benzethonium chloride assay (U/CSF protein, Roche Diagnostics,
Indianapolis, IN). Urine creatinine methods compared include an
enzymatic technique (CREA dry slide, Ortho-Clinical Diagnostics,
Rochester, NY) and a Jaffé reaction (Randox® creatinine, Equal
Diagnostics, Exton, PA). Data were analyzed by simple linear
regression scatterplots, Pearson’s correlation, and NCCLS EP9-A
difference and bias plot tests. Data were split and analyzed
separately for dogs and cats.
Linear regression analysis, correlation, bias data analysis for
canine urine samples
| |
VITROS (X) |
Hitachi (Y) |
Slope |
Intercept
(mg/dL) |
Correlation
(r) |
Mean
bias |
| Protein |
Pyrocatechol |
Benzethonium |
0.68 |
33.83 |
0.60 |
25.26 |
| Creatinine |
Enzymatic |
Jaffé |
1.03 |
-7.78 |
0.98 |
-2.21 |
| Ratio |
VITROS UPC |
Hitachi UPC |
0.26 |
0.35 |
0.47 |
0.05 |
Linear regression analysis, correlation, bias data analysis for
feline urine samples
| |
VITROS (X) |
Hitachi (Y) |
Slope |
Intercept
(mg/dL) |
Correlation
(r) |
Mean
bias |
| Protein |
Pyrocatechol |
Benzethonium |
0.48 |
50.70 |
0.85 |
-3.70 |
| Creatinine |
Enzymatic |
Jaffé |
1.02 |
2.04 |
0.97 |
6.99 |
| Ratio |
VITROS UPC |
Hitachi UPC |
0.64 |
0.19 |
0.99 |
-0.25 |
This study demonstrates that urine protein and urine creatinine
concentrations can vary depending on methodology, thereby making
interlaboratory UPC comparisons problematic. When monitoring renal
disease, serial UPC determinations require using the same methodology
as the baseline. If a new methodology is used, a new baseline must
be established.
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