The goal of this study is to learn if the TGFR device (which uses telmapirazin to continuously measure real-time GFR) works to provide accurate and dynamic kidney function assessment in critically ill adults with acute kidney injury (AKI). It will also learn how tGFR compares with the gold standard measured GFR (mGFR) and other commonly used estimate methods. The main questions it aims to answer are:

• Does tGFR show good agreement with mGFR over the 0-12 hour period in AKI patients?
• How do tGFR, mGFR, 4-hour creatinine clearance, kinetic GFR (keGFR), and CKD-EPI eGFR compare across different AKI stages?
• What are the bias and variability of each method over time?

Researchers will compare tGFR to mGFR (iohexol clearance) to see if tGFR is a reliable alternative for bedside, continuous GFR monitoring. They will also compare tGFR against 4-hour creatinine clearance, keGFR, and eGFR to assess consistency across AKI stages.

Participants will:

• Wear a single-use tGFR sensor patch on the chest for continuous GFR monitoring
• Receive iohexol injection for mGFR measurement (gold standard)
• Provide blood and urine samples for 4-hour creatinine clearance and other tests
• Undergo repeated GFR assessments over the 12-hour study period

Inclusion Criteria:

• CU stay ≤ 72 hours;
• meets KDIGO AKI criteria;
• age 18-85 years;
• able to complete blood/urine collection and monitoring

Exclusion Criteria:

• prior history of CKD stage 4 or higher;
• anuria;
• recent contrast agent exposure or kidney transplant history;
• pregnancy or breastfeeding; expected survival < 24 hours.