Variations of urinary N-acetyl-β-D-glucosaminidase levels and its performance in detecting acute kidney injury under different thyroid hormones levels: a prospectively recruited, observational study

OBJECTIVE: Changes in thyroid function will be accompanied by changes in urinary N-acetyl-β-D-glucosaminidase (uNAG) levels. Therefore, whether thyroid hormones interfere the ability of uNAG in detecting acute kidney injury (AKI) has raised concern in patients with critical illness. DESIGN: A prospectively recruited, observational study was performed. SETTING: Adults admitted to the intensive care unit of a grade A tertiary hospital in China. PARTICIPANTS: A total of 1919 critically ill patients were enrolled in the study. MAIN OUTCOME MEASURES: To investigate the variations of the ability of uNAG to detect AKI in patients with critical illness under different thyroid hormones levels (differences in area under the curve (AUC) for uNAG diagnosis and prediction of AKI with different thyroid hormones levels). RESULTS: The bivariate correlation analysis revealed that FT3 and TT3 levels were independently associated with uNAG levels (p<0.001). FT3 and uNAG also showed correlation in multivariable linear regression analysis (p<0.001). After stratification according to the levels of FT3 or TT3, significant variation was observed in the uNAG levels with different quartiles (p<0.05). However, in patients with varying FT3 and TT3 levels, no significant difference was found in the AUCs of uNAG to detect AKI (p>0.05). CONCLUSIONS: Even if uNAG levels varied with FT3 and TT3 levels, these hormones did not interfere with uNAG’s ability to detect AKI in patients with critical illness.