Lateral Flow Immunoassay Using Europium (III) Chelate Microparticles and Time-Resolved Fluorescence for Eosinophils and Neutrophils in Whole Blood

Abstract

Abstract Background: A simple point-of-care method for measuring leukocyte counts in a doctor’s office or emergency room could be of great importance. We developed a protocol for measuring cell count by disrupting the cell membrane and analyzing specific proteins within the cells and used it to analyze proteins from eosinophils and neutrophils. Methods: Lateral immunochromatographic (ICR) assays have been developed for eosinophil protein X (EPX) and human neutrophil lipocalin (HNL) as measures of the concentration of eosinophils and neutrophils. The correlation between the lateral ICR assays and cell counting of eosinophils and neutrophils was performed manually and with an automated cell counter. RIA assays measuring the same analytes were also compared with the results from cell counting and lateral ICR assays. Results: The optimized assays showed analytical detection limits below the clinical ranges of 3.36 μg/L and 2.05 μg/L for EPX and HNL, respectively. The recovery was 114.8%–122.8% for EPX and 94.5%–96.9% for HNL. The imprecision was 3%–17% CV for EPX over the whole range and 5%–16% CV for HNL. The correlation coefficients between manually counted cells and lateral ICR assays were 0.9 and 0.83 for EPX and HNL, respectively. Conclusion: The numbers of eosinophils and neutrophils in small amounts of blood can be estimated in the point-of-care setting by means of fast lateral ICR assays of EPX and HNL.