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We report the case of a newborn whose complete blood count showed unusual interferences on the XN-series analyzer (Sysmex, Kobe, Japan). Venipuncture was performed on the back of the hand after the administration of local anesthesia with a Eutectic Mixture of Local Anesthetics (EMLA) patch (Aspen, France). White blood cell (WBC) scattergram was abnormal, with unidentified populations (red arrows) leading to an overestimation of the raw WBC count in the WBC differential and white cell nucleated channels (panel A). Platelet counts also showed discrepancies with an overestimation of the optical platelet counts (not shown). Purple crystal-shaped fragments of various sizes displaying branching patterns were observed on the blood smear after May-Grünwald Giemsa staining (panel B: blood smear, 50× and 100× objectives).

Surcharging blood samples with the EMLA patch emulsion led to the same interferences on the different XN channels and blood smears. Therefore, we concluded that during blood collection from our patient, the cleaning procedure was insufficient, resulting in the contamination of the blood sample with residual EMLA premedication. This case shows a rare interference in hematology analyzers and how blood smear examination can detect it. It highlights the importance of pre-analytical steps to obtain reliable results.

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2023
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