NAG is a protein excreted in urine in cases of tubular damage, and is considered a biomarker of kidney injury. Elevated urinary NAG is seen after cardiac surgery, but the clinical significance, pattern of excretion and links to perioperative factors are poorly described. We plan a study of the pattern of NAG-excretion during cardiac surgery with cardiopulmonary bypass, and explore possible associated variables.

The standard biomarker of AKI, serum creatinine, has poor specificity and sensitivity in the early phases of renal injury. Since the therapeutic window is likely to be in the earlier stages before renal injury is manifest, there is a need for novel diagnostic methods. In the recent years, several new biomarkers of kidney injury have been introduced. To date, none has proven outstanding regarding precision in early detection of AKI. NAG (N-acetyl-b-D-glucosaminidase) is a lysosomal enzyme with high molecular weight. Due to its size, NAG does not normally pass the glomerulus apparatus, but urine levels are elevated after tubulus damage. NAG excretion in urine is seen in AKI after cardiac surgery, exposure to nephrotoxic agents and after renal transplantation. However, its role in clinical decision-making is yet to be established.

We aim to study the excretion pattern of urinary NAG during and after cardiac surgery with cardiopulmonary bypass. Association with perioperative variables will be explored.

Inclusion Criteria:

• Expected cardiopulmonary bypass time exceeding 60 minutes
• Elective surgery

Exclusion Criteria:

• End-stage kidney disease with dialysis
• Ongoing treatment with nephrotoxic antibiotic agent

60 patients scheduled for complex cardiac surgery