Urine SDS-PAGE and Cystatin B in the Diagnosis of Kidney Disease

Urinary tests beyond standard urinalysis and the urine protein:creatinine ratio (UPC) have only relatively recently been introduced, with little published information regarding the two most recently offered tests: SDS-PAGE and Cystatin B (CysB). 
Urine SDS-PAGE involves separation of urinary proteins by their molecular weight (i.e., size) in order to distinguish glomerular from tubular damage / dysfunction, and the number and intensity of the bands corresponds with the severity of damage. Indications for urine SDS-PAGE testing include determining whether renal proteinuria is glomerular or tubular in origin, monitoring the response to treatment for renal proteinuria, and determining suspicion for particular diagnostic categories of renal disease. 
Urinary CysB has been shown to originate from damaged renal tubular epithelial cells; therefore, its increased presence in the urine is thought to represent renal tubular injury. Several studies demonstrate its elevation in dogs with conditions that commonly result in acute kidney injury, and it could serve as an early indicator of tubular damage in patients at risk of kidney injury, even if GFR markers remain unchanged. Additionally, a higher baseline urinary CysB in dogs presenting with acute kidney injury is associated with decreased survival. In dogs with chronic kidney disease, there is evidence that urinary CysB can distinguish between those with stable versus progressive disease. 
This session will discuss these two urinary tests of kidney disease, integrating case examples and polling to highlight indications for testing and test interpretation as well as possible test interferences.