Preoperative Concentrated Urine Increases the Incidence of Plasma Creatinine Elevation After Major Surgery.

Postoperative elevation of plasma creatinine is a frequent complication to major surgery. A rise by 50% fulfills the criterion for Acute Kidney Injury. We studied the relationship between concentrated urine before surgery, which is usually a sign of chronically low intake of water, and the perioperative change in plasma creatinine. The creatinine concentration was measured in plasma and urine just before and at 6 h, 1 day, and 2 days after major abdominal surgery in a consecutive series of 181 patients. Receiver operating curve analysis was used to find the optimal cut-off to separate concentrated from diluted urine. Urine creatinine of 11.3 mmol/L before the surgery started was exceeded in one third of the patients and associated with greater increase in plasma creatinine at 6 h (median 21 vs. 10%) and at 1 day postoperatively (21 vs. 7%; < 0.0001). Elevation of plasma creatinine of >25% occurred in 41% and 19% in those with high and low urine creatinine, respectively ( < 0.001) and an increase by >50% in 16% and 10% ( = 0.27). Patients with high urine creatinine before surgery failed to further concentrate their urine during the perioperative period, which is normally associated with intensified renal fluid conservation. High urinary concentration of creatinine before surgery should be considered as a risk factor for postoperative elevation of plasma creatinine. The mechanism is probably that the renal threshold is then more easily reached.