Meredith P Schuh1, Edward Nehus1, Qing Ma1, Christopher Haffner1, Michael Bennett1, Catherine D Krawczeski2, Prasad Devarajan3. 1. Division of Nephrology, Cincinnati Children's Hospital Medical Center, University of Cincinnati, Cincinnati, OH. 2. Division of Pediatric Cardiology, Lucile Packard Children's Hospital, Stanford University, Palo Alto, CA. 3. Division of Nephrology, Cincinnati Children's Hospital Medical Center, University of Cincinnati, Cincinnati, OH. Electronic address: prasad.devarajan@cchmc.org.
Abstract
BACKGROUND: Recent meta-analyses support the utility of urinary biomarkers for the diagnosis and prognosis of acute kidney injury. It is critical to establish optimal sample handling conditions for short-term processing and long-term urinary storage prior to widespread clinical deployment and meaningful use in prospective clinical trials. STUDY DESIGN: Prospective study. SETTING & PARTICIPANTS: 80 children (median age, 1.1 [IQR, 0.5-4.2] years) undergoing cardiac surgery with cardiopulmonary bypass at our center. 50% of patients had acute kidney injury (defined as ≥50% increase in serum creatinine from baseline). PREDICTORS: We tested the effect on biomarker concentrations of short-term urine storage in ambient, refrigerator, and freezer conditions. We also tested the effects of multiple freeze-thaw cycles, as well as prolonged storage for 5 years. OUTCOMES: Urine concentrations of neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule 1 (KIM-1), and interleukin 18 (IL-18). MEASUREMENTS: All biomarkers were measured using commercially available kits. RESULTS: All 3 biomarkers were stable in urine stored at 4°C for 24 hours, but showed significant degradation (5.6%-10.1% from baseline) when stored at 25°C. All 3 biomarkers showed only a small although significant decrease in concentration (0.77%-2.9% from baseline) after 3 freeze-thaw cycles. Similarly, all 3 biomarkers displayed only a small but significant decrease in concentration (0.84%-3.2%) after storage for 5 years. LIMITATIONS: Only the 3 most widely studied biomarkers were tested. Protease inhibitors were not evaluated. CONCLUSIONS: Short-term storage of urine samples for measurement of NGAL, KIM-1, and IL-18 may be performed at 4°C for up to 24 hours, but not at room temperature. These urinary biomarkers are stable at -80°C for up to 5 years of storage. Our results are reassuring for the deployment of these assays as biomarkers in clinical practice, as well as in prospective clinical studies requiring long-term urine storage.
BACKGROUND: Recent meta-analyses support the utility of urinary biomarkers for the diagnosis and prognosis of acute kidney injury. It is critical to establish optimal sample handling conditions for short-term processing and long-term urinary storage prior to widespread clinical deployment and meaningful use in prospective clinical trials. STUDY DESIGN: Prospective study. SETTING & PARTICIPANTS: 80 children (median age, 1.1 [IQR, 0.5-4.2] years) undergoing cardiac surgery with cardiopulmonary bypass at our center. 50% of patients had acute kidney injury (defined as ≥50% increase in serum creatinine from baseline). PREDICTORS: We tested the effect on biomarker concentrations of short-term urine storage in ambient, refrigerator, and freezer conditions. We also tested the effects of multiple freeze-thaw cycles, as well as prolonged storage for 5 years. OUTCOMES: Urine concentrations of neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule 1 (KIM-1), and interleukin 18 (IL-18). MEASUREMENTS: All biomarkers were measured using commercially available kits. RESULTS: All 3 biomarkers were stable in urine stored at 4°C for 24 hours, but showed significant degradation (5.6%-10.1% from baseline) when stored at 25°C. All 3 biomarkers showed only a small although significant decrease in concentration (0.77%-2.9% from baseline) after 3 freeze-thaw cycles. Similarly, all 3 biomarkers displayed only a small but significant decrease in concentration (0.84%-3.2%) after storage for 5 years. LIMITATIONS: Only the 3 most widely studied biomarkers were tested. Protease inhibitors were not evaluated. CONCLUSIONS: Short-term storage of urine samples for measurement of NGAL, KIM-1, and IL-18 may be performed at 4°C for up to 24 hours, but not at room temperature. These urinary biomarkers are stable at -80°C for up to 5 years of storage. Our results are reassuring for the deployment of these assays as biomarkers in clinical practice, as well as in prospective clinical studies requiring long-term urine storage.
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