SDMA case study: Zeke
SDMA helps unmask chronic kidney disease in a hyperthyroid cat
Age: 14 years
Breed: Domestic shorthair
Gender: Neutered male
Presenting reason and history
Zeke’s owners were concerned that he seemed to be eating a lot but losing weight. They also noticed him drinking and urinating more and meowing more than he usually does. His owners said he seemed to be active, but they were concerned that his habits at home were not normal for him.
Zeke was thin with a low body condition score (BCS) of 2.5 on 9-point scale. He had moderate dental disease, a rapid heart rate, and a palpable nodule in his neck area.
Complete blood count (CBC); chemistry panel, including the IDEXX SDMA Test and electrolytes; complete urinalysis; and total T4 were recommended. Zeke’s CBC results were within normal limits. Other findings are shown here.
- Based on history, physical examination, and laboratory results, Zeke was diagnosed with hyperthyroidism.
- An increased SDMA* result guides us to investigate further: Chronic kidney disease (CKD) is a progressive disorder that may exist alongside other medical conditions. While attention to the hyperthyroid condition was a medical priority, based on the diagnostics performed, the kidneys required investigation and support as well.
- Possible further diagnostic investigation: Thoracic and abdominal imaging can help confirm and assess the medical conditions identified within the blood and urine diagnostics as well as other organ system impact (e.g., heart). An electrocardiogram would assess cardiac conductivity. Measurement of blood pressure was encouraged, as both kidney disease and hyperthyroidism are associated with high blood pressure. A urine culture and minimum inhibitory concentration (MIC) susceptibility and urine protein:creatinine (UPC) ratio are commonly performed as part of a complete kidney workup, also.
Diagnosis and case follow-up
Because Zeke’s owner had a difficult time pilling him, his hyperthyroidism was successfully treated with I-131, and he was ultimately diagnosed with concurrent International Renal Interest Society (IRIS) CKD Stage 2 disease.
- One month following treatment with I-131, Zeke’s total T4 level was at 0.7 μg/dL, his SDMA was measured at 17 μg/dL, and his creatinine increased from 0.9 to 1.8 mg/dL. His urine remained poorly concentrated, with specific gravity of 1.014.
- SDMA continues to indicate issues with kidney function, even though creatinine is within normal limits.
- Zeke did not return to his veterinarian for several months, but a recheck of his laboratory work at that time confirmed that his hyperthyroidism had been successfully treated. He continued to have an increased SDMA, a normal creatinine, and dilute urine.
- Following the IRIS CKD Staging Guidelines, Zeke has IRIS CKD Stage 2 disease. Without SDMA, his CKD would have gone undiagnosed. Zeke’s veterinarian followed the IRIS CKD Treatment Guidelines to treat him, which could help delay the progression of Zeke’s CKD and even extend his life.
Follow-up laboratory results
Zeke’s case reinforces that SDMA is more reliable than creatinine as a biomarker of kidney health.1–5 In this particular example, SDMA was more reliable than creatinine and accurately reflected loss of renal function, while creatinine underestimated renal function because of Zeke’s loss of lean muscle mass.
Both kidney disease and hyperthyroidism are common medical conditions in older cats. Further challenging the reliability of creatinine in this case was the concurrent hyperthyroidism, which increases metabolism and artificially increases glomerular filtration rate (GFR). Diagnosing chronic kidney disease in hyperthyroid cats is challenging. Creatinine, being a by-product of muscle, is underproduced in feline hyperthyroidism as a result of muscle loss and becomes a poor indicator of kidney function.
- 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. Vet J. 2014;202(3):588–596.
- Hall JA, Yerramilli M, Obare E, Yerramilli M, Melendez LD, Jewell DE. Relationship between lean body mass and serum renal biomarkers in healthy dogs. J Vet Intern Med. 2015;29(3):808–814.
- Nabity MB, Lees GE, Boggess M, et al. Symmetric dimethylarginine assay validation, stability, and evaluation as a marker for early detection of chronic kidney disease in dogs. J Vet Intern Med. 2015;29(4):1036–1044.
- 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. J Vet Intern Med. 2014;28(6):1676–1683.
- Hall JA, Yerramilli M, Obare E, Yerramilli M, Almes K, Jewell DE. Serum concentrations of symmetric dimethylarginine and creatinine in dogs with naturally occurring chronic kidney disease. J Vet Intern Med. 2016;30(3):794–802.