SDMA case study: Reese
SDMA helps lead to the diagnosis and treatment of suspect pyelonephritis and improvement in kidney function
Age: 16 years
Breed: Domestic shorthair
Gender: Spayed female
Presenting reason and history
Reese presented for her annual wellness examination. The owners felt that Reese was doing well for a senior cat. Her appetite was good, and they had not noticed any weight loss, coughing, sneezing, vomiting, diarrhea, or change in thirst or urination.
Reese was bright, alert, responsive, and hydrated. She was a little overweight with a body condition score (BCS) of 6 on a 9-point scale. Her temperature, pulse, and respiration were within normal limits. Thoracic auscultation and abdominal palpation were normal, and the remainder of the physical examination was unremarkable.
Complete blood count (CBC); chemistry panel, including the IDEXX SDMA Test and electrolytes; complete urinalysis; and total T4 were recommended for a senior wellness minimum database. Reese’s CBC results were within normal limits. Other findings are shown here.
Reese’s diagnostic results showed an increased SDMA* along with a normal creatinine and increased BUN. She also had inappropriate urine concentrating ability with a urine specific gravity of 1.018. In addition, Reese had an active urine sediment with >100 WBC/hpf and marked bacteriuria. Based on these findings, a urine culture and susceptibility were performed and >100,000 organisms/mL of Escherichia coli were grown that were susceptible to most antibiotics, including amoxicillin and amoxicillin/clavulanic acid.
Based on Reese’s increased SDMA with an inappropriately low urine specific gravity, it was clear that she had decreased kidney function in addition to having a urinary tract infection.
Differentials at this time included:
- Active or acute kidney injury (AKI) secondary to pyelonephritis.
- Chronic kidney disease (CKD) with a concurrent lower urinary tract infection (UTI).
- AKI from pyelonephritis superimposed on CKD, causing a worsening of existing kidney disease.
Additional diagnostics that should have been considered to investigate further but were not performed:
- Abdominal ultrasound to look for evidence of pyelonephritis and rule out urolithiasis
- Blood pressure, since hypertension is a common confounding factor with kidney disease, and measurement of a urine protein:creatinine ratio or UPC
- Amoxicillin/clavulanic acid 62.5 mg by mouth twice daily for 1 month for possible pyelonephritis
- Fresh, clean water sources available at all times
- Diet changed to kidney-therapeutic diet
- Ideally, recheck is scheduled in 2 weeks to determine response to treatment.
- However, recheck was done in 1 month to see if infection cleared and if kidney function improved.
- Follow-up diagnostics revealed that the SDMA concentration had decreased from 19 μg/dL to 15 μg/dL, there were no white blood cells or bacteria on the urine sediment, and the culture was negative.
Diagnosis and long-term management
- Suspect pyelonephritis based on improvement in kidney function after treatment of UTI.
- Acute kidney injury (AKI) from pyelonephritis superimposed on CKD.
- Treat for International Renal Interest Society (IRIS) stage 2 CKD, including continuing to feed a kidney therapeutic diet.1
- Recheck urine culture monthly for 3 consecutive months upon a negative result.
- Then recheck minimum database and urine culture every 3 months.
Urine culture and MIC susceptibility
- SDMA is a more sensitive indicator of kidney function than creatinine in AKI as well as CKD and increases earlier.2–4
- In pets like Reese, an increased SDMA in the face of a urinary tract infection should lead to additional investigation and a consideration for more aggressive treatment for pyelonephritis.
- Long-term management and monitoring of these pets can help detect future infections promptly for early treatment and slow progression of CKD.
- International Renal Interest Society. IRIS Guidelines. www.iris-kidney.com/guidelines. Accessed January 22, 2019.
- 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.