Veterinary session

SDMA (symmetric dimethylarginine) is an endogenous methylated form of the arginine that is released into circulation during normal protein catabolism. It is a new biomarker for the early detection of kidney dysfunction in human and small animal medicine. SDMA is not reabsorbed through the renal tubules, and non-renal factors other than feed do not affect its excretion. The aim of this current study was to determine SDMA concentration and reference values in a larger population of healthy horses, furthermore, to compare SDMA, urea and creatinine values of healthy horses with a group of standardbred horses (when hypovolemia can develop after the race  standardbred group), and with a clinically sick group of horses (patients with chronic or acute renal failure).

Blood samples were taken from a total of 145 horses to measure SDMA, Crea, and urea concentrations. 95 healthy horses were included in the control group, when the SDMA was measured with the „gold standard” HPLC-MS method, so that a reference range and its correlation with breed, age, gender, fitness, and nutritional status was determined. 22 standardbred horses were included in the second group of horses and the 3 parameters were measured prior and after the race. 28 clinical patients were included in the sick group: 21 acute kidney injury (AKI) and 7 chronic renal disease (CRD) cases. Biochemistry values were compared among the three groups.

In the group of healthy horses, all three parameters were within the reference range: mean SDMA 7.2 (+1.27) µg/dL, urea 5.1 (0.89) mmol/L, Crea 104.1 (22.5) µmol/L. In the group of standardbred horses all three post-training parameters showed a slight increase compared to pre-race values. Comparing the pre-race values with the post-race values, the changes in Crea and urea were strongly correlated, with SDMA moderately. In the group of sick horses at AKI cases mean SDMA 12.9 (+5.6), Crea 263.2 (+90), urea 15.45 (+78) all increased compared to control horses. In the CRD group multiple values were measured: SDMA 87.1 (+100), Crea 482 (+307.6), urea 25 (+12.8). In horses with AKI, SDMA elevation moderately correlated with Crea elevation, but showed good correlation in horses with CRD. In all horses studied, urea and creatinine both correlated with SDMA elevation, Crea more.

Overall, serum SDMA concentrations were elevated in both AKI and CRD horses, however, in 8 AKI horses, SDMA was physiological, so acute hypovolemia and azotaemia were not always associated with high SDMA values. Similarly, SDMA did not appear to be a more sensitive marker in racehorses, however, further studies are warranted.