Proteinuria associated with AKI, readmissions in surgical patients

Preoperative urinalysis assessments to identify patients at risk for acute kidney injury (AKI) may improve outcomes, according to the study authors, who called for prospective studies on the topic.

Preoperative proteinuria may indicate higher risk for postoperative acute kidney injury (AKI) and unplanned 30-day readmission, according to a new study.

Researchers performed a retrospective, population-based study in patients with and without known preoperative renal dysfunction who were having elective inpatient surgery at 119 Veterans Affairs facilities from Oct. 1, 2007, to Sept. 30, 2014. Preoperative proteinuria was defined as the closest value within six months of surgery, as assessed by urinalysis, in one of five categories: negative (0 mg/dL), trace (15 to 29 mg/dL), 1+ (30 to 100 mg/dL), 2+ (101 to 300 mg/dL), and 3+ (301 to >1,000 mg/dL). Patients were considered to have normal preoperative renal function if their estimated glomerular filtration rate (eGFR) was above 60 mL/min/1.73 m2. The study's primary outcome was postoperative AKI before discharge and unplanned readmission within 30 days. Results were published online July 3 by JAMA Surgery.

A total of 153,767 nonemergent surgeries in 134,765 patients met the inclusion criteria. Of these, 37.1% were orthopedic, 28.8% were general, and 13.8% involved vascular procedures. The patients' mean age was 63.7 years, and most patients were white (80.6% ) and male (93.2%). Overall, 86,631 surgeries (56.3%) were in patients with no proteinuria, 31,738 (20.6%) were in the trace category, 24,511 (16%) were in the 1+ category, 8,511 (5.5%) were in the 2+ category, and 2,376 (1.6%) were in the 3+ category. In the trace, 1+, 2+, and 3+ categories, 20.4%, 14.9%, 4.3%, and 0.9% of patients, respectively, had a normal eGFR before surgery.

Unadjusted analyses found a significant association between preoperative proteinuria and both postoperative AKI and readmission (negative, 8.6% and 9.3%; trace, 12% and 11.3%; 1+, 14.5% and 13.3%; 2+, 21.2% and 15.8%; and 3+, 27.6% and 17.5% [P<0.001 for all comparisons]). After adjustment, a dose-response relationship was observed between preoperative proteinuria and both postoperative AKI (odds ratios, 1.2 [95% CI, 1.1 to 1.3] in the trace category vs. 2.0 [95% CI, 1.8 to 2.2] in the 3+ category) and 30-day unplanned readmission (odds ratios, 1.0 [95% CI, 1.0 to 1.1] in the trace category vs. 1.3 [95% CI, 1.1 to 1.4] in the 3+ category).

The authors noted that they could not assign causation due to their study's observational, retrospective design and that preoperative urinalysis is not routinely performed on all patients, among other limitations. They concluded that preoperative proteinuria appears to be a marker of perioperative risk for AKI and readmission in patients with and without renal dysfunction before surgery. “Identification and early intervention with patients at risk for AKI (eg, patients with diabetes, chronic kidney disease) through preoperative urinalysis assessments may improve patient outcomes by alerting care teams of excess risk despite normal eGFR,” the authors wrote. “Future prospective studies are warranted to further understand how preoperative proteinuria affects perioperative outcomes.”