Although acute kidney injury (AKI) frequently complicates cardiac surgery, methods to determine AKI risk are lacking. Renal functional reserve (RFR), the capacity of the intact nephron mass to increase glomerular filtration rate (GFR), represents maximal filtration capacity. We hypothesized that preoperative RFR would predict postoperative AKI.

Acute kidney injury (AKI) is a frequent complication in patients undergoing cardiac surgery with an estimated prevalence of 36%. However, clinicians have limited tools to preoperatively identify patients at risk for AKI and/or progression to chronic kidney disease, particularly in patients with normal resting glomerular filtration rate (rGFR). Renal functional reserve (RFR) describes the capacity of the intact nephron mass to increase GFR from baseline in response to stimuli (e.g., protein load). We hypothesized that the presence or absence of RFR could separate patients at risk for developing AKI from patients with better-preserved renal function and a more favorable short- and long-term prognosis despite identical rGFR. The aim of this study is to examine whether preoperative assessment of RFR is able to predict risk for AKI after cardiac surgery.

Inclusion Criteria:

1. Subjects older than 18 years
2. Subjects undergoing elective cardiac surgery
3. Subjects who signed informed consent forms

Exclusion Criteria:

1. Pregnancy
2. Chronic kidney disease ≥ stage III
3. Solitary kidney
4. Diabetes mellitus type 1
5. Recent cardiac arrest
6. Liver failure or cirrhosis
7. Total parenteral nutrition
8. Hemoglobin <11 g/dl
9. Sepsis
10. History of malabsorption, chronic inflammatory bowel disease, short bowel, or pancreatic insufficiency
11. Transplant donor or recipient
12. Active autoimmune disease with renal involvement
13. Rhabdomyolysis
14. Prostate hypertrophy with International Prostate Symptom Score ≥20
15. Neoplasm

Withdrawal criteria:

All patients included in the study were to be followed up until the scheduled end of the study. Data collection could be terminated prior to the scheduled time only under the following conditions:

• General criteria

  1. A patient or his/her legal representative may refuse further participation in the study at any time (withdrawal of consent),

  2. The investigator may withdraw a patient from the participation in the study at any time for the following reasons:

     • a severe protocol violation,
     • the development of incidents/near-incidents/other severe clinical complications related to the study protocol

• Criteria related to the study

  1. Subjects who could not stop taking angiotensin-converting enzyme inhibitors and/or angiotensin II receptor blockers a minimum of 48 hours before the protein load.
  2. Subjects who received non-steroidal anti-inflammatory drugs within the 48 hours before the protein load.
  3. Subjects who received intravenous radiocontrast agents within the 72 hours before the protein load.

Adult patients undergoing elective cardiac surgery