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Does this form of testing hold the key to diagnosing deterioration of the kidney in cats earlier?
Why they did it
Chronic kidney disease in cats is often not recognized in the clinical setting until there is evidence of azotemia and loss of urine concentrating ability. Identification of sensitive serum biomarkers, which would allow early identification of cats with renal disease, would facilitate early intervention and improve patient care. Symmetric dimethylarginine (SDMA) has been found to be an accurate surrogate for estimated glomerular filtration rate (GFR) in people and a more sensitive biomarker of renal function. These studies sought to evaluate the utility of this biomarker in the setting of feline renal disease.
What they did
Three studies have evaluated the possible role of SDMA as a biomarker for feline renal disease.
In the first article (“Comparison of serum concentrations of symmetric dimethylarginine and creatinine as kidney function biomarkers in cats with chronic kidney disease”), the authors retrospectively reviewed SDMA and serum creatinine concentrations in 15 cats with azotemia for ≥ three months, four nonazotemic cats with a greater than 30% decrease in GFR from normal, and two nonazotemic cats with calcium oxalate kidney stones. Data from 21 healthy geriatric cats were also evaluated. Over a six-month period prior to enrollment, these cats had three normal GFR test results, three normal serum creatinine concentrations and three urine specific gravity assessments > 1.040.
In the second article (“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 authors fed control food or one of two experimental diets supplemented with fatty acids to 32 healthy cats. Cats were fed these diets for six months, and serum chemistry profiles, including SDMA and serum creatinine concentrations, GFR, and metabolic profiles, were performed at baseline and at 1.5, three and six months.
In the third article (“Relationship between serum symmetric dimethylarginine concentration and glomerular filtration rate in cats”), the authors sought to determine whether SDMA concentrations would rise as expected in cats with reduced GFR. GFR was measured by using iohexal clearance in 10 client-owned cats. All cats were > 11 years of age, and both azotemic and nonazotemic cats were included.
What they found
In the first article, the authors found that both SDMA and serum creatinine concentrations correlated well to changes in GFR. However, SDMA was elevated before the serum creatinine concentration in 81% of cats (17 of the 21 subjects) by a mean of 17 months (range, 1.5 to 48 months). SDMA was elevated in all nonazotemic cats with a subnormal GFR. The SDMA and serum creatinine concentrations remained within the reference range for all the healthy geriatric cats.
In the second article, the authors found that diets supplemented with fatty acids did not result in any changes to renal biomarkers over the six-month period. However, they did find that SDMA appeared to be a more sensitive marker of renal dysfunction over that time frame, particularly in older cats with decreased lean body mass. The authors noted that serum creatinine concentrations were positively correlated with total lean mass and that as total lean mass declined with age, serum creatinine concentrations declined as well. Conversely, SDMA concentrations did not correlate in the same manner with lean body mass; these concentrations increased in cats with declining GFR and body mass.
In the final article, the researchers found a reciprocal linear relationship between the decline in GFR and elevations in SDMA concentration. And as expected, a direct linear relationship was also noted between SDMA and serum creatinine concentrations.
These results suggest that SDMA is a sensitive biomarker for early detection of feline kidney disease. Further studies will be needed to determine if early intervention in these cases will result in improved outcomes.
Hall JA, Yerramilli M, Obare E, et al. Comparison of serum concentrations of symmetric dimethylarginine and creatinine as kidney function biomarkers in cats with chronic kidney disease. J Vet Intern Med 2014;28(6):1676-1683.
Link to abstract: http://www.ncbi.nlm.nih.gov/pubmed/25231385
Hall JA, Yerramilli M, Obare E, et al.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. Vet J 2014;202(3):588-596.
Link to abstract: http://www.sciencedirect.com/science/article/pii/S1090023314004341
Braff J, Obare E, Yerramilli M, et al. Relationship between serum symmetric dimethylarginine concentration and glomerular filtration rate in cats. J Vet Intern Med 2014;28(6):1699-1701.
Link to abstract: http://onlinelibrary.wiley.com/doi/10.1111/jvim.12446/abstract