Using renal tubular enzymes to identify renal damage earlier

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About 66% to 75% of nephrons are no longer functioning by the time traditional blood and urine test results reveal renal abnormalities in dogs. So an earlier method to detect kidney tubular damage would be of great benefit. Researchers have proposed using the renal tubular enzymes N-acetyl-beta-D-glucosaminidase (NAG) and gamma-glutamyl transpeptidase (GGT) as indicators of early disease. A recent study in the American Journal of Veterinary Research sought to establish reference ranges in adult dogs for these two enzymes so that abnormal results can be identified. The researchers collected urine samples from 38 client-owned healthy dogs by using antepubic cystocentesis and measured NAG and GGT activities.

The results:

Reference range for GGT activity in dogs: 1.93 to 28.57 U/g

Reference range for NAG activity in dogs: 0.02 to 3.63 U/g

No difference was found between males and females for GGT activity, but there was a difference for NAG activity. So the reference ranges adjusted for sex for NAG activity were 0.02 to 3.65 U/g for male dogs and 0.02 to 2.31 U/g for female dogs. No differences were seen with changes in body surface area, but the GGT reference ranges were higher in dogs with a urine pH of 7 or above. The researchers concluded that GGT and NAG activities above these reference ranges may indicate renal tubular damage earlier than normal blood and urine testing. Urine GGT and NAG assays are available through most commercial laboratories and are cost-effective. Their use in detecting early renal tubular injury could prompt management changes that decrease morbidity and mortality in affected patients.

Brunker JD, Ponzio NM, Payton ME. Indices of N-acetyl-beta-D-glucosaminidase and gamma-glutamyl transpeptidase activities in clinically normal adult dogs. Am J Vet Res 2009;70(2):297-301.

Link to abstract: http://avmajournals.avma.org/doi/abs/10.2460/ajvr.70.2.297