SDMA

 
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SDMA (symmetric dimethylarginine) is the amino acid, arginine, that contains two methyl groups (dimethyl) in a symmetrical orientation. SDMA is considered a sensitive and early marker (more sensitive than serum creatinine) of declining GFR in dogs and cats (Hokamp and Nabity 2016 review).

Physiology

SDMA is produced by all nucleated cells at a constant rate, with highest concentrations in the brain, and is excreted primarily by the kidneys, with some evidence of liver uptake in humans. It does not appear to be reabsorbed in renal tubules or influenced by many non-renal factors, other than diet (Hokamp and Nabity 2016 review).

Methodology

SDMA testing is currently not offered by Cornell University. The gold standard method is high performance liquid chromatography-mass spectrophotometry, however an immunologic-based assay has been developed and is in current use (Hokamp and Nabity 2016 review).

Units of measurement

SDMA is measured in μg/dL (conventional units) or μmol/L (SI units).

Sample considerations

Sample type

Serum, heparinized plasma

Stability

Stable in canine and feline samples for one week at room temperature, 14 days at 4ºC and over a year frozen at -20 or -80ºC (Hokamp and Nabity 2016 review).

Test interpretation

Studies in dogs and cats to date show a good correlation (around 70-80%) between SDMA and GFR (as measured by inulin or iohexol clearance in some studies) and it is currently thought to be a more sensitive marker of GFR than creatinine, although few studies have been performed to date (Hokamp and Nabity 2016 review,

Increased serum/plasma cystatin C concentrations

A recommended upper limit of a reference interval for dogs and cats is 14 μg/dL (Hokamp and Nabity 2016 review).
  • Pathophysiologic: As indicated above, measurement of SDMA is currently being used as a sensitive and early marker of decreased GFR in dogs and cats (Hokamp and Nabity 2016 review).

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