A correction formula for neuron-specific enolase measurement in hemolyzed neonatal serum samples

As a specific biomarker in neonatal hypoxic-ischemic encephalopathy (HIE), the measurement of neuron-specific enolase (NSE) has been advocated as a predictor of outcome in neurological injury. However, the measured levels of NSE may be influenced by hemolysis. In the current study, the change in the concentration of NSE in serum was measured by chemiluminescence prior to and following the addition of individual frozen and thawed red blood cells from 86 neonates that were collected within 24 h of birth. The changes in the concentration of NSE were compared with the changes in the concentration of hemoglobin (Hb), measured by the hemoglobin cyanide (HiCN) method, to establish a correction formula. The performance of the correction formula was evaluated by comparing the corrected concentration of NSE using the individual constants and the correction formula. The average individual constant of NSE from the 86 hemolyzed neonatal serum samples was 25.15±3.94 mg/g Hb. The concentration variation between NSE and Hb in neonatal sera could be described by the equation ΔNSE_serum=1.8594+24.0670 xΔHb_HiCN (r²=0.8045, P<0.001). There was no statistically significant difference in the NSE corrected results between the individual constant group and the correction formula group (Z=-1.645, P=0.100). The linear regression formula of Hb measured with the instrumental method compared with the HiCN method was Hb_instr=0.9816×Hb_HiCN+0.5596 (r²=0.9924, P<0.001). Based on these regression analyses, the correction formula for NSE in hemolyzed neonatal serum was determined as NSE_corr=NSE_meas-24.0670×Hb_HiCN-1.8594 or NSE_corr=NSE_meas-24.5181×Hb_instr+11.8609. In conclusion, hemolysis has a substantial influence on the accurate measurement of NSE in neonatal serum samples. For hemolyzed neonatal serum samples, correcting the NSE results using a correction formula is essential to evaluate the severity of neonatal hypoxic ischemic encephalopathy.