Time-Dependent EDTA Effect on Leukocyte Differential Count and Morphology Compared to Blood Smear Made by Direct Finger Prick.

Introduction: The impact of ethylenediaminetetraacetic acid (EDTA) on leukocyte count and morphology has led to the current recommendation that smears made from EDTA blood should be prepared within 4 h of sampling. However, previous studies have only been performed on smears with normal cell counts, and smears made from K₂EDTA blood have not been studied in comparison with smears made from direct finger prick. The aim of this study was to investigate the time limit for performing a morphological assessment on smears from EDTA blood without compromising the results.

Methods: Blood samples from 37 patients with known or suspected abnormal leukocyte morphology were selected, with smears from direct finger prick used as controls. Smears were prepared from the original EDTA tube every 4 h up to 24 h after sampling. The smears were evaluated for differential count, morphological assessment, and smear quality scoring.

Results: No significant difference in cell count was observed on smears made up to 12 h after sampling for neutrophils (p = 0.430), lymphocytes (p = 0.080), monocytes (p = 0.948) eosinophils (p = 0.398), basophils (p = 0.460), and blast cells (p = 0.239) compared to smears made by finger prick. However, smears prepared later than 8 h postsampling showed a significant increase in morphological changes.

Conclusion: A manual differential leukocyte count can be reliably performed on smears from EDTA blood within 12 h, whereas a comprehensive morphological assessment requires smears to be prepared within 8 h of sampling.