White blood cell counts by automated and manual methods with backlighting

Area of Science:

• Hematology
• Clinical Pathology
• Laboratory Medicine

Background:

• Automated hematology analyzers, like the Coulter S-Plus Jr, provide rapid white blood cell (WBC) counts.
• Specimen interferences, such as platelet aggregates, can lead to questionable automated results, often indicated by a "backlighting" flag.
• Ethylenediamine tetraacetic acid (EDTA) is a common anticoagulant used in blood collection, but its different salt forms may affect analytical accuracy.

Purpose of the Study:

• To compare automated WBC counts flagged with backlighting from samples collected in sodium EDTA (Na 2EDTA) and potassium EDTA (K 3EDTA) against manual hemocytometer counts.
• To investigate the causes of backlighting interference in automated WBC counts.
• To determine the preferred EDTA salt form for accurate automated whole blood analysis.

Main Methods:

• Comparison of automated WBC counts from Coulter S-Plus Jr with backlighting against manual hemocytometer counts.
• Analysis of 29 automated backlighted WBC counts from Na 2EDTA and K 3EDTA anticoagulated samples.
• Microscopic smear examination to identify interfering factors like platelet clumps and large platelets.

Main Results:

• Automated WBC counts with backlighting showed good agreement with manual counts.
• Platelet aggregates and large platelets were identified in 66% of samples collected in Na 2EDTA tubes, causing interference.
• Backlighting in K 3EDTA tubes was primarily associated with low WBC counts, not platelet interference.

Conclusions:

• Platelet interference is a significant cause of backlighting in automated WBC counts using Na 2EDTA.
• K 3EDTA is a superior anticoagulant for whole blood analysis, minimizing platelet clumping and backlighting.
• Using K 3EDTA enhances the reliability of automated WBC counts by reducing analytical interferences.