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Effect of storage time on the urine protein: creatinine ratio in alkaline ovine urine.

ABSTRACT: The urine protein:creatinine (UPC) ratio is considered the reference method to assess proteinuria. Its diagnostic value in ovine medicine needs further elucidation. In population monitoring and/or for research purposes, it is convenient to collect many samples simultaneously and store them for later analysis. However, analyte stability data are required to ensure reliable results. We used 15 of 90 urine samples collected from sheep to assess the effect of storage time on the UPC ratio. After centrifugation, the supernatant of each sample was divided into 6 aliquots. Urine protein and creatinine concentrations were determined immediately in one aliquot using the pyrogallol red and a modified Jaffè method, respectively. The other aliquots were stored at -18°C. Based on the absence of active sediment, alkaline urine pH, and UPC ratio ≥0.2, we included 15 samples in our study. The UPC ratio was determined in the stored aliquots 2, 7, 14, 21, and 60 d after collection. The data were analyzed with univariate ANOVA. No significant difference was observed in the urinary concentrations of protein, creatinine, and the UPC ratio (0.8 ± 0.84 in conventional units and 0.09 ± 0.095 in SI units) among different times (p > 0.05). The UPC ratio remained stable for 2 mo in ovine urine samples stored at -18°C.

SUBMITTER: Athanasiou LV

PROVIDER: S-EPMC8546464 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Because there is substantial biologic intraindividual variation in albumin excretion, randomized trials of albuminuria-reducing therapies may need multiple urine samples to estimate daily urinary albumin excretion. Mailing spot urine samples could offer a convenient and cost-effective method to collect multiple samples, but urine albumin-to-creatinine ratio stability in samples stored at ambient temperatures for several days is unknown.Patients with kidney disease provided fresh urine samples in two tubes (with and without boric acid preservative). Reference aliquots from each participant were analyzed immediately, whereas remaining aliquots were subject to different handling/storage conditions before analysis, including delayed processing for up to 7 days at three different storage temperatures (4°C, 18°C, and 30°C), multiple freeze-thaw cycles, and long-term frozen storage at -80°C, -40°C, and -20°C. We calculated the mean percentage change in urine albumin-to-creatinine ratio for each condition, and we considered samples stable if the 95% confidence interval was within a ±5% threshold.Ninety-three patients provided samples with detectable albuminuria in the reference aliquot. Median (interquartile range) urine albumin-to-creatinine ratio was 87 (20-499) mg/g. The inclusion of preservative had minimal effect on fresh urine albumin-to-creatinine ratio measurements but reduced the changes in albumin and creatinine in samples subject to processing delay and storage conditions. The urine albumin-to-creatinine ratio was stable for 7 days in samples containing preservative at 4°C and 18°C and 2 days when stored at 30°C. It was also stable in samples with preservative after three freeze-thaw cycles and in frozen storage for 6 months at -80°C or -40°C but not at -20°C.Mailed urine samples collected with preservative and received within 7 days if ambient temperature is ?18°C, or within 2 days if the temperature is higher but does not exceed 30°C, are suitable for the measurement of urine albumin-to-creatinine ratio in randomized trials. Preserved samples frozen to -40°C or -80°C for 6 months before analysis also seem suitable.

Project description:BackgroundAlthough measuring albuminuria is the preferred method for defining and staging chronic kidney disease (CKD), total urine protein or dipstick protein is often measured instead.ObjectiveTo develop equations for converting urine protein-creatinine ratio (PCR) and dipstick protein to urine albumin-creatinine ratio (ACR) and to test their diagnostic accuracy in CKD screening and staging.DesignIndividual participant-based meta-analysis.Setting12 research and 21 clinical cohorts.Participants919 383 adults with same-day measures of ACR and PCR or dipstick protein.MeasurementsEquations to convert urine PCR and dipstick protein to ACR were developed and tested for purposes of CKD screening (ACR ≥30 mg/g) and staging (stage A2: ACR of 30 to 299 mg/g; stage A3: ACR ≥300 mg/g).ResultsMedian ACR was 14 mg/g (25th to 75th percentile of cohorts, 5 to 25 mg/g). The association between PCR and ACR was inconsistent for PCR values less than 50 mg/g. For higher PCR values, the PCR conversion equations demonstrated moderate sensitivity (91%, 75%, and 87%) and specificity (87%, 89%, and 98%) for screening (ACR >30 mg/g) and classification into stages A2 and A3, respectively. Urine dipstick categories of trace or greater, trace to +, and ++ for screening for ACR values greater than 30 mg/g and classification into stages A2 and A3, respectively, had moderate sensitivity (62%, 36%, and 78%) and high specificity (88%, 88%, and 98%). For individual risk prediction, the estimated 2-year 4-variable kidney failure risk equation using predicted ACR from PCR had discrimination similar to that of using observed ACR.LimitationDiverse methods of ACR and PCR quantification were used; measurements were not always performed in the same urine sample.ConclusionUrine ACR is the preferred measure of albuminuria; however, if ACR is not available, predicted ACR from PCR or urine dipstick protein may help in CKD screening, staging, and prognosis.Primary funding sourceNational Institute of Diabetes and Digestive and Kidney Diseases and National Kidney Foundation.

Project description:Urine albumin-creatinine ratio (ACR) and protein-creatinine ratio (PCR) are important markers of kidney damage and are used for prognosis in persons with chronic kidney disease (CKD). Despite how commonly these measurements are done in clinical practice, relatively few studies have directly compared the performance of these 2 measures with regard to associations with clinical outcomes, which may inform clinicians about which measure of urinary protein excretion is best. We studied the association of ACR and PCR with common complications of CKD.Cross-sectional study.3,481 participants with CKD in the Chronic Renal Insufficiency Cohort (CRIC) Study.ACR and PCR.We examined the association between ACR and PCR with measures of common CKD complications: serum hemoglobin, bicarbonate, parathyroid hormone, phosphorus, potassium, and albumin.Restricted cubic spline analyses adjusted for estimated glomerular filtration rate (eGFR; calculated by the MDRD [Modification of Diet in Renal Disease] Study equation) were performed to study the continuous association with our predictors with each outcome.Mean eGFR was 43±13 (SD)mL/min/1.73 m2 and median values for PCR and ACR were 140 and 46 mg/g, respectively. In continuous analyses adjusted for eGFR, higher ACRs and PCRs were similar and both were associated with lower serum hemoglobin, bicarbonate, and albumin levels and higher parathyroid hormone, phosphorus, and potassium levels. Across all outcomes, the associations of ACR and PCR were similar, with only small absolute differences in the outcome measure. Similar associations were seen in patients with diabetes mellitus.Participants largely had moderate CKD with low values for ACR and PCR, so results may not be generalizable to all CKD populations.In persons with CKD, ACR and PCR are relatively similar in their associations with common complications of CKD. Thus, routine measurement of PCR may provide similar information as ACR in managing immediate complications of CKD.

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Effect of storage time on the urine protein: creatinine ratio in alkaline ovine urine.

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