Analytical quality performance goals for symmetric dimethylarginine in cats

Background: Symmetric dimethylarginine (SDMA) reflects the glomerular filtration rate (GFR) in people, dogs, and cats. Initial assays used a liquid chromatography-mass spectroscopy (LC) technique. A veterinary immunoassay has been developed for use in commercial laboratories and point-of-care (POC) laboratory equipment. There have been no independent assessments of these assays, and analytical performance goals for SDMA testing have not been defined. Objectives: This study sought to establish analytical performance goals for SDMA in cats from (a) biological variation (BV) data and (b) expert opinion. Methods: Analytical performance goals were determined from a prior BV study of SDMA in cats and a survey of veterinary internists who have used SDMA in practice. Results: Biological variation-based performance goals included an imprecision of +/- 10% (immunoassay and LC), bias of +/- 8% (immunoassay and LC), and total error of +/- 24% (immunoassay and LC). Expert opinion performance goals were +/- 0.10 mu mol/L (+/- 2 mu g/dL), or +/- 0.15 mu mol/L (+/- 3 mu g/dL), varying with starting SDMA concentrations. Conclusions: This study recommends analytical performance goals for SDMA based on BV and expert opinion. Wide dispersion of SDMA results using currently available assays implies that clinicians risk attaching medical significance to small SDMA changes that actually reflect analytical variability.