N-Acetyl-ß-D-Glucosaminidase Index as an Early Biomarker for Chronic Renal Insufficiency in Cats with Hyperthyroidism
Hyperthyroid cats are at risk of developing chronic renal insufficiency (CRI) and diagnostic tools currently used to screen for renal insufficiency in hyperthyroid cats are either not reliable or impractical. The aim of this study was to determine whether n-acetyl-ß-D-glucosaminidase index (NAG) was a good biomarker for chronic renal insufficiency (CRI) in these cats.
Twenty-four newly diagnosed hyperthyroid cats with a normal renal biochemical profile and ten healthy (H) cats were enrolled and evaluated for HT4 at baseline. Hyperthyroid cats were started on methimazole and they were reevaluated once euthyroid. At the end of the study, three groups were discemed: H, normal euthyroid (NE) and euthyroid cats with CRI (ECRI). Baseline group characteristics were scrutinized to predict CRI. NAGi over time was also evaluated.
Baseline NAGi was significantly different between groups (P=.004). ECRI had a higher median value (13.12 U/g) when compared to H (1.38 U/g). NAGi values decreased significantly over time in NE. Using a NAGi > 2.76 U/g, negative and positive predictive values for CRI were 77.7% and 50%, while the combination of a urinary specific gravity (USG) < 1.035 and a T4 > 7.80 µg/dl enhance prediction level to 88.9% and 83.3%, respectively.
NAGi did not differentiate NE from ECRI at baseline. However, it appears to be a biomarker for active renal damage during HT4. The combination USG-T4 could optimize the identification of appropriate candidates for definitive treatment of HT4. NAGi could also be used to adjust methimazole dosage during medical treatment.