EVALUATION OF THE AUTOMATED LEUKOCYTE COUNT AND DIFFERENTIAL FROM THECELL-DYN(R)-3500 IN SICKLE-CELL DISEASE

Erythrocytes resistant to standard lysing reagents are known to occur in sickle cell disease. These lyse-resistant erythrocytes can cause ab errant automated leucocyte counts and differentials. The ability of th e Cell-Dyn(R) 3500 automated haematology analyser to eliminate resista nt erythrocytes and accurately count and differentiate leucocytes was evaluated. Samples were obtained from paediatric patients with sickle cell disease or haemoglobin SC disease. The Cell-Dyn(R) 3500, using im pedance and optical counting with a hypotonic salt 'extended lyse mode ', was compared to the Cell-Dyn(R) 3000, an optical analyser that also uses a hypotonic salt lyse, the Cell-Dyn(R) 400, a 'hard detergent ly se' impedance counter, and a reference 400-cell manual white cell diff erential (National Committee for Clinical Laboratory Standards [NCCLS] Approved Guideline H20-A). Seventy-Eve samples from patients with sic kle cell disease or haemoglobin SC disease were evaluated for total le ucocyte count, percentage of lymphocytes, percentage of neutrophils, a nd nucleated red blood cells (NRBC) nags. The Cell-Dyn(R) 3500 correla ted well with Cell-Dyn(R) 400 leucocyte counts, with a correlation coe fficient of 0.95. When compared to the manual differential, the correl ation coefficient for lymphocytes was 0.93 and for neutrophils 0.95. T he Cell-Dyn(R) 3500 NRBC nag had a sensitivity of 47.7% and a specific ity of 80.6%. The predictive value of a positive nag was 77.7%. The Ce ll-Dyn(R) 3500's extended lyse mode clearly enhances the accuracy of l eucocyte counts and differentials in patients with sickle cell disease .