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The presence of proteinuria may be telling of poor surgical outcomes for patients regardless of their estimated glomerular filtration rate (eGFR), according to a retrospective analysis.

Among those getting elective inpatient surgeries (n=153,767) performed at 119 Veterans Affairs facilities, 43.8% had had some degree of proteinuria on urinalysis in the 6 months preceding surgery, reported Mary Hawn, MD, MPH, of Stanford University, Calif., and colleagues.

Proteinuria was tied to postoperative acute kidney injury (AKI) in a dose-dependent relationship, with even trace amounts (15-29 mg/dL) linked to a slightly increased risk (adjusted OR 1.2, 95% CI 1.1-1.3) and class 3+ proteinuria (301-1,000 mg/dL) tied to doubled odds (adjusted OR 2.0, 95% CI 1.8-2.2), the researchers reported in .

Trace urine protein levels were also tied to 30-day unplanned readmissions (adjusted OR 1.0, 95% CI 1.0-1.1), as were class 3+ levels (adjusted OR 1.3, 95% CI 1.1-1.4).

"Proteinuria was associated with postoperative AKI and 30-day unplanned readmission independent of preoperative eGFR," Hawn's group concluded. "Simple urine assessment for proteinuria may identify patients at higher risk of AKI and readmission to guide perioperative management."

More likely to have preoperative proteinuria were patients with diabetes who were black and had chronic kidney disease, non-independent functional status, and a higher American Society of Anesthesiology class burden. These individuals in particular should be screened for proteinuria with a urine dipstick urinalysis, the investigators suggested.

"However, with proteinuria having an estimated prevalence between 8% and 33% in the general population, preoperative urinalysis assessments for proteinuria may be beneficial among all surgical patients. Assessing preoperative urine dipstick analysis for proteinuria ... regardless of baseline creatinine level or eGFR, may be a useful strategy for assessing the risk of postoperative AKI because proteinuria can manifest before changes in eGFR and serum creatinine level," according to the group.

For now, urine testing is not the current standard of care in the U.S. even though patients undergoing elective surgery often already receive preoperative evaluation with routine laboratory work consisting of a basic metabolic profile (with serum creatinine levels and eGFRs provided), a complete blood cell count, and coagulation assessment, the investigators said.

Their retrospective population-based study included a cohort of mostly elderly white men who underwent surgery in 2007-2014; excluded were those having cardiac, transplantation, and urology procedures.

Orthopedic (37%), general (29%), and vascular procedures (14%) were found to be the most common surgeries in the dataset.

"Further investigations are warranted, including detailed cost-effectiveness analyses for preoperative urinalysis assessment," the researchers noted.

They added that the retrospective nature of the study left room for selection bias and residual confounding despite multivariable adjustment.

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