Aim To identify and report the falsely elevated white cell count associated with the use of soft paraffin and avoid unnecessary anxiety associated with this.

Method We analysed the blood samples collected with the assistance of paraffin and without the assistance of paraffin and analysed it using the common Full blood count analyser Sysmex XE 2100. Some of the blood samples were spiked with paraffin and analysed to see if consistent results can be produced.

Results Samples with paraffin were noted to have higher white cell count (up to 50%) compared to the true value. The soft paraffin can get dispersed in the blood sample. Being similar in size to the white cell volume, the paraffin globules scatter the laser light in a similar way to white cell count and affect the total white cell count, falsely elevating the white cell count. They produce a characteristic short broad curve.

Conclusion Paraffin used to assist blood sampling can cause false leucocytosis. Neonatal full blood counts with elevated white cell count need to be considered with caution when paraffin is used to assist the collection of the blood sample.