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An Urban Experience
cat USG should exceed 1.035-40 although is frequently much higher in young cats. Dogs and cats with tubular disease will often have reduced concentrating ability but it is possible for both to retain a degree of concentrating ability particularly in the early stages of disease and therefore isosthenuria (USG 1.008-1.0150) is not a requirement for a diagnosis of renal disease. For patients with primary glomerular disease, urine concentrating ability may be normal given the location of the pathology.
Urinalysis including dipstick evaluation and sediment examination is an important component of assessing for renal disease. Dipstick assessment may give information relating to proteinuria but should be interpreted in light
of the urine specific gravity and may also be informative in terms of tubular function e.g. glucosuria and pH. Sediment examination can be important for identification of an active sediment e.g. urinary tract infection or pyelonephritis, but may also reveal changes such as crystalluria or cast formation. Ultimately if proteinuria is suspected or staging for proteinuria (see below) is being performed it is important to ensure that pre- and post- renal causes of proteinuria have been excluded and that quantitative assessment with a urine protein to creatinine ratio (UPC) is performed.
Diagnostic imaging may also form part of the diagnostic investigation of a patient with suspected kidney disease. Ultrasound is of particular use for evaluating the size, shape and architecture of the kidney. This may provide supporting evidence for whether a disease process is acute or chronic and may identify complicating factors such as nephro- or ureterolithiasis. However, again normal renal architecture does not preclude the presence of kidney disease, for example in patients with primary glomerular disease renal ultrasound may be considered unremarkable. Abdominal radiographs may be useful for patients where there is a suspicion for urolithiasis and contrast imaging may sometimes be performed e.g. anterograde pyelogram where there is concern regarding ureteral obstruction.
Having made a diagnosis of kidney disease it is widely recommended that staging according to the International Renal Interest Society (IRIS) is performed for patients with chronic disease. It is fundamental that staging is only performed after the diagnosis of CKD has been made and that patients are considered to have stable disease at the time of staging. Any pre-renal azotaemia should be corrected before staging is performed. IRIS have also recently released a grading system that is used for classification of AKI. Further details can be found at
Having made a diagnosis of CKD, individuals will be placed into a stage based on their plasma creatinine concentration. Note that patients in IRIS stage 1 and early IRIS stage 2 CKD may have Substaging should then be performed using both proteinuria (UPC
evaluation) and blood pressure. Phosphorus targets are also available in terms of optimal stage specific management of CKD-mineral and bone disorder. The criteria for IRIS staging can be found here: http://www.
Reflecting the evidence that SDMA may be able to identify an earlier stage of disease than creatinine concentration and that it may be of particular use in assessing GFR in patients with poor muscle condition, IRIS have recently released guidlelines for the use of SDMA within their CKD staging system: http://www. For example, a persistently elevated SDMA in a patient where creatinine is within reference interval is supportive of IRIS stage 1 disease. Note the importance of documenting that the elevation of SDMA is persistent in this situation with at least two samples obtained ideally 2-4 weeks apart. Similarly the addition of SDMA to the staging system allows patients with poor muscle condition to be more accurately classified in a potentially higher stage for management and treatment recommendations. It is likely that the use of SDMA for the management of both CKD and AKI will evolve as we become more familiar as clinicians with the utility of this marker.
Additional reading (1-6)
1. Relford R, Robertson J, Clements C. Symmetric Dimethylarginine: Improving the Diagnosis and Staging of Chronic Kidney Disease in Small Animals. Veterinary Clinics of North America: Small Animal Practice. 2016 11;46(6):941-60.
2. 30(3):794-802
3. Hall JA, Yerramilli M, Obare E, Yerramilli M, Jewell DE. Comparison of Serum Concentrations of Symmetric Dimethylarginine and Creatinine as Kidney Function Biomarkers in Cats with Chronic Kidney Disease. Journal of Veterinary Internal Medicine. 2014;28(6):1676-83.
4. Nabity MB, Lees GE, Boggess MM, Yerramilli M, Obare E, Yerramilli M, et al. Symmetric Dimethylarginine Assay Validation, Stability, and Evaluation as a Marker for the Early Detection of Chronic Kidney Disease in Dogs. Journal of Veterinary Internal Medicine. 2015;29(4):1036-44.
5. Jepson RE, Syme HM, Vallance C, Elliott J. Plasma asymmetric dimethylarginine, symmetric dimethylarginine, L-arginine and nitrite/nitrate concentrations in cats with chronic kidney disease and hypertension. J Vet Int Med. 2008;22:317-24.
6. Hall JA, Yerramilli M, Obare E, Yerramilli M, Yu S, Jewell DE. Comparison
of serum concentrations of symmetric dimethylarginine and creatinine as kidney function biomarkers in healthy geriatric cats fed reduced protein foods enriched with fish oil, L-carnitine, and medium-chain triglycerides. The Veterinary Journal. 2014 12//;202(3):588-96.

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