This week’s case featured an 84-year-old male referred after routine blood tests showed an extremely elevated white cell count. He reported increasing fatigue but no other significant symptoms.

Summary of key findings:

• WBC: 823 ×10⁹/L
• Exceeded analyser linearity → dilution required for accurate quantitation
• RBC: 2.69 ×10¹²/L
• Hb: 84–106 g/L (corrected for WBC interference)
• Platelets: 164 ×10⁹/L

Blood film features:

• A pleomorphic population of lymphocytes
• Small to medium-sized cells with a high nuclear-cytoplasmic ratio
• Clumped (“soccer-ball”) chromatin
• Occasional prolymphocytes
• Presence of smear cells

These features are classical for CLL. The combination of a markedly elevated lymphocyte count, characteristic morphology, and a supporting clinical picture strongly points to chronic lymphocytic leukaemia as the final diagnosis.

Dealing with results outside the analyser linearity range:

This case also raised an interesting challenge from an analytical perspective. How do we deal with results that are outside the linearity range of an analyser? Best practice includes:

• Performing a manual or automated dilution of the sample using the analyser’s recommended protocol
• Repeating the test on the diluted specimen to obtain a reliable, linear result (remember to multiply the diluted result by the dilution factor to get the actual result!)
• Documenting the action including the dilution factor
• Correcting impacted parameters, such as haemoglobin (WBC interference), if required
• Reviewing histograms/scatterplots for flagging patterns that may require additional checks