Variability of Symmetric Dimethylarginine in Apparently Healthy Dogs

BackgroundSymmetric dimethylarginine (SDMA) is a screening tool for early kidney dysfunction and monitoring treatment in cases of chronic kidney disease (CKD). There are no current studies describing the suitability of this test for use with published population-based reference intervals. Hypothesis/ObjectivesTo determine the components of biological variability, the index of individuality (IOI), the critical difference between sequential measurements (C-D) and the number of measurements required to assess the homeostatic set point (HSP), for both SDMA and serum creatinine (sCr), in apparently healthy dogs. AnimalsTwenty apparently healthy adult dogs owned by clients or staff at a veterinary teaching hospital. MethodsProspective, observational study. Blood was collected from each dog on 9 occasions, and SDMA and sCr were measured in duplicate using commercially available assays. ResultsSDMA and sCr had intermediate and low IOI values of 0.87 and 0.28, respectively. The C-D of SDMA and sCr, was 1.34 mu g/dL and 0.89 mu mol/L, respectively. The sample numbers required for estimation of an individual's HSP (with 90 and 95% CI) for SDMA and sCr were 8 and 45, and 2 and 12 sequential measurements, respectively. Conclusions and Clinical ImportanceBased on our findings, in comparison to sCr, SDMA is better suited for use with population-based reference intervals. False-negative test results could occur when comparing a single test result from an individual to such intervals. Ideally C-D should be used with sequential measurements.