Peer-reviewed veterinary case report
How do storage factors affect urine tests for kidney disease in cats?
By Mortier, Femke et al.·Published in Journal of veterinary internal medicine·2023·Small Animal Department·View original on PubMed →
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Original publication title: Effect of laboratory and sample storage factors on urinary protein:creatinine ratios and clinical decision making in cats.
- Species:
- cat
Plain-English summary
This study looked at how different laboratories and storage methods can affect the results of urinary protein:creatinine ratios (UPC) in cats, which are important for diagnosing and managing chronic kidney disease. Researchers tested urine samples from 60 cats, sending them to multiple labs and storing them under various conditions. They found that while short-term storage (up to a week) didn't significantly change the UPC results, long-term storage (more than six months) could lead to different interpretations of the protein levels in some cases. In fact, half of the cats had at least one lab that gave a different classification for their protein levels. Overall, the study suggests that where and how urine samples are stored can impact clinical decisions, especially over longer periods.
Abstract
BACKGROUND: Urinary protein:creatinine ratio (UPC) results affect the diagnosis, prognosis, and therapy of chronic kidney disease in cats. OBJECTIVES: To investigate the interlaboratory and intralaboratory variability and the effect of storage on UPC and International Renal Interest Society (IRIS) proteinuria substaging in cats. ANIMALS: Healthy and diseased client-owned cats. METHODS: Prospective study. Urine of 60 cats was randomly sent to 4 (of 9) participating laboratories (to assess interlaboratory variability) and per cat, 2 laboratories each received 2 aliquots (to determine intralaboratory variability). Samples of 23 cats were analyzed in the same laboratory the day of collection, after preservation at 22°C for 1 day and at 4°C during 1-7 days (short-term storage) and at -24°C and -80°C for 6-12 months (long-term storage). Storage conditions were compared by equivalence testing. RESULTS: UPCs showed good interclass correlation (ICC-inter, 0.90) and excellent intraclass correlation (ICC-intra, 0.99). However, in 30/60 (50%) cats at least 1 of 4 laboratories assigned a different IRIS proteinuria substage. Urinary protein:creatinine ratio remained stable with short-term storage, but not after 6 months storage at -24°C and after 12 months storage at -24°C or -80°C. Long-term storage caused a change in IRIS proteinuria substage in 27% of cats, whereas a shift occurred only in 4% of cats during short-term storage. CONCLUSIONS AND CLINICAL IMPORTANCE: Laboratory choice for UPC measurement can result in different IRIS substaging for the same cat, whereas urine storage at room temperature for 1 day or in the refrigerator for up to 7 days does not clinically affect UPC.
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Search related cases →Original publication on PubMed: https://pubmed.ncbi.nlm.nih.gov/37015881/