SDMA Values: Interpretation & Application

In the literature

Baral RM, Freeman KP, Flatland B. Analytical quality performance goals for symmetric dimethylarginine in cats. Vet Clin Pathol. 2021;50:57-61.

The Research …

Symmetric dimethylarginine (SDMA) is a biomarker used to assess glomerular filtration rate in the diagnosis, classification, and monitoring of chronic kidney disease. Veterinary immunoassays have been developed for regular use in commercial laboratories and point-of-care laboratory equipment but have not been evaluated independently. 

This study attempted to identify intraindividual analytic performance goals (ie, imprecision, bias, total error) using both reference laboratory and in-clinic assay data and determine what internal medicine specialists considered to be acceptable analytical variability in SDMA values. Comparison revealed marked discordance between performance capability of the tests and clinician expectations for test performance; clinicians expected much less variability. 

Clinicians risk attributing significance to and overinterpreting small changes in SDMA that may reflect either normal changes in the individual patient or analytical variability. An individual patient may have a normal analyte result whether healthy or sick, but the population-derived reference cutoff points may not apply to that patient. Changes (ie, trends) in an individual patient may be more meaningful. Information regarding reference change intervals that can aid in interpreting results is available (see Suggested Reading).¹ In addition, breed variation is significant for SDMA, creatinine, glucose, and total protein values. Age variation has also long been recognized for numerous analytes. 

This study evaluated SDMA, but biologic and analytic variations apply to all tests used in veterinary medicine.²

… The Takeaways

Key pearls to put into practice:

• History, physical examination findings, and clinical insight may be more important than laboratory test results.

• Trends in an individual patient may be more important than single measurements.

• Regular screening in healthy and sick patients can generate meaningful data that can aid in making medical decisions.

• In-clinic laboratory equipment should regularly undergo quality control.¹