Dimensionality reduction identified 4 candidate proteins (FABP3, REST, IL-6, NF-H) that were integrated with spinal cord–derived cfDNA to derive the Spinal Cord Injury Index (SCII), which has high sensitivity and specificity for SCI diagnosis (AUC: 0.91, 95% CI 0.82–0.99, P < 0.0001), correlates with injury severity (P < 0.0001), and predicts 6-month neurologic improvement (AUC: 0.77, 95% CI 0.61–0.93, P = 0.006). The gene discussed is NEFH; the disease is spinal cord injury.