Acute Kidney Injury Biomarker Analysis at the Point-of-care in Critically Ill Neonates

Background: Acute kidney injury (AKI) contributes to mortality and morbidity in critically ill neonates. Current AKI definitions are based on serum creatinine (Cr) levels: however, analysis of multiple biomarkers including Neutrophil Gelatinase-Associated Lipocalin (NGAL) and Cystatin C (CysC) may help to differentiate the etiology, differentiate between a change in kidney function vs. tissue injury, and determine injury progression. These biomarkers are not currently suitable for rapid clinical diagnosis due to long assay turnaround times and the relatively large sample volume required for existing tests. Therefore, AKI testing in newborns using small volumes of sample, preferably in real-time, using near patient methods may greatly improve the ability to optimize care.

Methods: We developed a novel, near-patient digital microfluidic (DMF) platform to combine biochemical and immunoassays using disposable cartridges that are preloaded with dried assay reagents (R44HD095225). A biochemical assay for Cr and immunoassays for NGAL and CysC were programmed on the cartridge. Sample input is 50 µL of whole blood or urine.

Results: The analytical performance of Cr, CysC, and NGAL assays was evaluated using blood samples. Precision in blood was 5.97, 4.48 and 12.98% for Cr, CysC, and NGAL, respectively, at low concentrations and 6.46, 4.3 and 8.05% at high concentrations. Linearity was excellent for all three analytes across the clinically relevant ranges for newborns: 0.14 -400 mg/dL for Cr, 13.2-300 ng/mL for NGAL, and 0.2 – 6,480 ng/mL for CysC. Method comparison analysis for the Cr and CysC assays using both blood and urine samples showed high correlation of the DMF assays to standard reference methods: correlation values of 0.86 (Cr – blood), 0.88 (CysC – blood), 0.98 (Cr – urine), 0.88 (NGAL – urine), and 0.86 (CysC – urine).

Conclusion: A digital microfluidic cartridge can perform both biochemical (Cr) and immunoassays (NGAL, CysC) from both urine and blood samples. A wide measurement range has been achieved to accommodate both types of samples, some of which have non-overlapping concentrations. Such assay integration and sample breadth allow maximizing diagnostic yield from limited samples available which is critical in neonates. Though further clinical validation is required, these multiple biomarker assays can provide clinicians with a comprehensive understanding of kidney function and injury in neonates with limited sample volume.