Investigation of the association between serum amyloid A concentrations and proteinuria in cats

Objectives: Evaluate the association between serum amyloid A [SAA] concentrations and proteinuria in cats without known pre-renal, renal and post-renal causes of proteinuria and to document the magnitude of proteinuria in these cases. Methods: Cats with contemporaneous SAA and urine protein: creatinine ratio (UPC) data and without renal azotaemia, evidence of reduced urine concentrating ability, active urine sediment, hyperthyroidism, diabetes mellitus and recent steroid administration were included. Cats with SAA >3.9 µg/dL were classified as having increased SAA. UPC was compared between cats with and without increased SAA using the Mann Whitney U test, comparisons between the proportion of cases classified as proteinuric (UPC>0.4 or UPC >0.2) between the groups were made using the Fisher’s Exact test and correlations were assessed using Spearman’s correlation coefficient. Multivariable logistic regression analysis was performed to examine the association between SAA and UPC. Results: UPC was significantly higher in the increased SAA group than in the normal SAA (0.32 [0.11-1.25] vs. 0.17 [0.08-0.59]; P=0.002) and cats with increased SAA were also more likely to be borderline or overtly proteinuric (UPC >0.2) than cats in the normal SAA group (72% vs. 36%; P=0.02). There was also a moderate positive correlation between UPC and SAA (rs=0.519; P<0.001). Conclusions and relevance: increased urine protein: creatinine ratio is associated with increased SAA concentrations in cats, although the severity of proteinuria in these cases is usually mild. Systemic inflammation might contribute to proteinuria in some cats, although further studies are required to establish a causal relationship.