Electrophoretic patterns of proteinuria in feline spontaneous chronic kidney disease

Objectives: The purpose of this study was to describe the electrophoretic patterns of proteinuria in cats at risk of and cats with chronic kidney disease (CKD), and to investigate whether the presence of high-molecular-weight (HMW) and low-molecular-weight (LMW) proteins were associated with CKD, proteinuria and/or disease progression. Methods: Healthy cats at risk of developing renal disease (n = 17) and cats affected with CKD at different stages (n = 22) were prospectively enrolled and sampled over time. Seventy urine samples were included and assayed with a commercially available sodium dodecyl sulfate–agarose gel electrophoresis (SDS-AGE) method. Each sample (gel lane) was inspected to identify albumin, HMW and LMW proteins, and an electrophoretic pattern (albuminuria, glomerular, tubular, mixed or negative) were assigned accordingly. Fisher’s exact test was used to assess the distribution of HMW and LMW proteins in cats grouped according to International Renal Interest Society stage and to the magnitude of proteinuria, and to assess if HMW and LMW proteins at the time of inclusion were associated with development and progression of CKD. Results: In samples of cats at risk, the most common pattern was glomerular (84.6%); glomerular pattern was also common in cats with CKD (54.2%), although mixed proteinuria and tubular proteinuria were also present (29.5% and 11.4%, respectively). The presence of LMW proteins was associated with CKD (P <0.0001) and to a urine protein:creatinine ratio >0.2 (P = 0.025). Both HMW and LMW proteins were not associated with progression of CKD within 6 months (n = 14). Conclusions and relevance: Our results showed that HMW proteinuria is common in healthy cats at risk of developing CKD, although the pathological significance needs to be confirmed. The detection of LMW proteins in urine of cats suspected to be affected by CKD, especially in non-azotaemic, non-proteinuric or borderline proteinuric cats, suggests the presence of kidney damage.