Serum concentrations of symmetric dimethylarginine and creatinine in cats with kidney stones

Abstract

Serum concentrations of symmetric dimethylarginine (SDMA) correlate with renal function in cats and SDMA has been shown to be a more reliable and earlier marker for chronic kidney disease (CKD) compared with serum creatinine (Cr). Calcium oxalate uroliths tend to develop in mid-to-older aged cats and kidney stones may cause a reduction in renal function with increased SDMA, but normal serum Cr. The purpose of this retrospective study was to determine if cats with kidney stones had increased serum SDMA concentrations, and whether SDMA increased earlier than serum creatinine concentrations. Cats in the colony with kidney stones diagnosed between August 2010 and December 2015 (n = 43) were compared with healthy geriatric cats (n = 21) without kidney stones. Serum SDMA concentrations were determined by liquid chromatography-mass spectrometry and serum Cr concentrations were determined by enzymatic colorimetry. Cats with kidney stones were diagnosed antemortem by radiographic imaging (n = 12) or by postmortem necropsy (n = 31). Retrospectively, serum SDMA was found to be increased above the upper reference limit in 39 of 43 cats with kidney stones. Serum Cr was increased above the upper reference limit in 18 of 43 cats; 6 of these 18 cats had terminal azotemia only. The mean time that serum SDMA was increased before serum Cr was increased was 26.9 months (range 0 to 60 months). Kidney stones were composed of calcium oxalate in 30 of 34 cats. The lifespan for cats with kidney stones (mean, 12.5 years; range, 6.1 to 18.1 years) was shorter (P < 0.001) than for control cats (mean, 15.2 years; range, 13.0 to 17.2 years), suggesting that non-obstructive kidney stones have an effect on mortality rate or rate of CKD progression. In conclusion, if SDMA concentrations are elevated in mid-to-older aged cats, further imaging studies are warranted to check for the presence of kidney stones.

Fig 1. Serum SDMA concentrations are illustrated for healthy cats, cats with kidney stones diagnosed antemortem at the time of diagnosis, and cats with kidney stones diagnosed postmortem at the time of death.

The dashed horizontal red line represents the upper limit of the reference interval for serum SDMA concentration (< 14 μg/dL). Individual cats in each group are represented by a black dot. The horizontal blue line represents the mean serum SDMA concentration for the group. The number and percent of cats ≥14 μg/dL in each group are also indicated.

Fig 2. Serum Cr concentrations are illustrated for healthy cats, cats with kidney stones diagnosed antemortem at the time of diagnosis, and cats with kidney stones diagnosed postmortem at the time of death.

The dashed horizontal red line represents the upper limit of the reference interval for serum Cr concentration (2.1 mg/dL). Individual cats in each group are represented by a black dot. The horizontal blue line represents the mean serum Cr concentration for the group. The number and percent of cats ≥ 2.1 mg/dL in each group are also indicated.