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Kidney Injury

Preoperative Proteinuria and AKI: What’s the Connection?

Proteinuria—a known indicator of renal dysfunction in medical patients—is also associated with the risk for acute kidney injury (AKI) and short-term hospital readmission among surgical patients.1

Researchers made this determination based on findings from a study of 153,767 surgeries performed on patients with and without known preoperative renal dysfunction between October 1, 2007, and September 30, 2014.

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Urinalysis was performed to assess preoperative proteinuria. Each patient was placed in one of the following proteinuria categories:

  • Negative (0 mg/dL)
  • Trace (15 to 29 mg/dL)
  • 1+ (30 to 100 mg/dL)
  • 2+ (101 to 300 mg/dL)
  • 3+ (301 to 1000 mg/dL)
  • 4+ (more than 1000 mg/dL)

The primary outcome was defined as postoperative discharge AKI and 30-day unplanned readmission following discharge, while secondary outcomes included any 30-day postoperative events.

Of the 153,767 surgeries, most were orthopedic, general and vascular procedures (37%, 29%, and 14%, respectively). Approximately 43.8% of patients in this cohort demonstrated evidence of proteinuria:

  • Trace: 20.6% (proportion of patients with normal estimated glomerular filtration rate [eGFR]: 20.4%)
  • 1+: 16.0% (normal eGFR: 14.9%)
  • 2+: 5.5% (normal eGFR: 4.3%)
  • 3+: 1.6% (normal eGFR: 0.9%)

The researchers found that preoperative proteinuria was significantly associated with postoperative AKI (negative: 8.6%, trace: 12%, 1+: 14.5%, 2+: 21.2%, 3+: 27.6%) and 30-day unplanned readmission (negative: 9.3%; trace: 11.3%; 1+: 13.3%; 2+: 15.8%; 3+: 17.5%). A dose-dependent relationship was observed for both outcomes after adjustment.

The odds ratios (ORs) ranged from 1.2 for trace to 2.0 for 3+ for postoperative AKI, and from 1.0 for trace to 1.3 for 3+ for unplanned readmission.

The association of preoperative proteinuria with postoperative AKI was found to be independent of eGFR.

 “Simple urine assessment for proteinuria may identify patients at higher risk of AKI and readmission to guide perioperative management,” the researchers wrote.

—Christina Vogt

Reference:

1. Wahl TS, Graham LA, Morris MS, et al. Association between preoperative proteinuria and postoperative acute kidney injury and readmission [Published online July 3, 2018]. JAMA Surg. doi:10.1001/jamasurg.2018.2009