Serum symmetric dimethylarginine in older dogs: Reference interval and comparison of a gold standard method with the ELISA

Abstract

AbstractBackgroundSerum symmetric dimethylarginine (SDMA) is used to screen for renal dysfunction in dogs. The gold standard technique for measuring SDMA, liquid chromatography‐tandem mass spectrometry (LC‐MS/MS) is not widely available. Age‐specific reference intervals for SDMA in older dogs are lacking.ObjectivesProspective study in older dogs to validate a commercially available LC‐MS/MS method for SDMA, compare SDMA concentrations with concentrations measured using ELISA and obtain a reference interval (RI) for older dogs using both methods.AnimalsClient‐owned older dogs undergoing health screening.MethodsThe LC‐MS/MS method was analytically validated (limit of detection, precision, and linearity). Serum was sent cooled overnight for ELISA or was frozen at −80°C until batch analysis using LC‐MS/MS. Results of LC‐MS/MS and ELISA were compared and RIs for older dogs were calculated according to international guidelines.ResultsThe LC‐MS/MS method showed good linearity (r2 = .99) and precision (coefficient of variation <10%), with a laboratory RI between 8.0 and 14.0 μg/dL. Paired measurements were available from 118 different dogs. Median SDMA concentration were 9.4 (range, 5.0‐21.2) using LC‐MS/MS and 12.0 (range, 5.0‐22.0) μg/dL using ELISA. Both methods significantly differed with a mean difference of 2.2 μg/dL. The RI for older dogs for LC‐MS/MS was 4.4‐15.0 μg/dL, and for ELISA was 6.4‐17.4 μg/dL.Conclusions and Clinical ImportanceThe ELISA provided significantly higher SDMA concentrations compared to the validated LC‐MS/MS method, indicating the need for device‐ or assay‐specific RI. The obtained age‐specific RI for SDMA is considerably higher in older dogs compared to the general laboratory RI.