Neutrophil CD64 expression, a marker of sepsis/infection, can be performed on a hematology blood counter and has variable correlation to C-reactive protein, procalcitonin and soluble CD163
© BioMed Central Ltd 2007
Published: 26 September 2007
Neutrophil CD64 expression (PMN CD64) has been proposed as an improved laboratory indicator of severe infection and sepsis. Little is published on the interrelationship between PMN CD64 and the soluble phase indicators of inflammation, such as C-reactive protein (CRP), procalcitonin (PCT), and soluble CD163.
We studied PMN CD64 in three clinical groups: neonates (390 specimens), hospitalized patients (236 specimens), and ambulatory outpatients (96 specimens). PMN CD64 was measured as an index using the Leuko64 (Trillium Diagnostics). Samples were also processed in parallel for the measurement of CD64 using the Leuko64 assays for flow cytometry on a FACScan (Becton Dickinson) and the blood cell counter Cell Dyn Sapphire (Abbott Diagnostics). Data were analyzed using Leuko64 software (Trillium Diagnostics). Results from both platforms were expressed as the PMN CD64 index, the monocyte CD64 index, and the monocyte CD163 index. CRP was measured in parallel. Plasma samples were stored at -70°C for subsequent measurement of procalcitonin (B.R.A.H.M.S.) and soluble CD163 (Trillium Diagnostics).
PMN CD64 correlated best with CRP, closely followed by PCT, but the degree of correlation varied among the clinical groups. The correlation was best in neonates (r = 0.592 for CRP and r = 0.391 for PCT), followed by hospitalized patients (r = 0.345 for CRP and r = 0.349 for PCT), and less so in outpatients (r = 0.251 for CRP and r = 0.257 for PCT). The correlation between PMN CD64 and the soluble markers was higher than that between CRP and PCT (r = 0.331 for hospitalized patients, r = 0.305 for neonates, and r = 0.196 for ambulatory patients). Soluble CD163 levels only weakly correlated with PMN CD64, CRP and PCT. The Sapphire results were highly correlated with flow cytometry (r = 0.99). The measured level of imprecision of both assays was <12% CV for PMN CD64, monocyte CD64, and monocyte CD163 indices. The assay results were available in <1 hour.
This study shows a moderate correlation of PMN CD64 with the 'acute phase reactants' CRP and PCT. Soluble CD163 is only weakly correlated with the other parameters and may independently define further subsets of patients based upon different anti-inflammatory responses to the clinical condition. The interrelationship of these parameters varies in different clinical situations. We demonstrate it is feasible to automate cellular assays for infection/sepsis in a routine hematology laboratory providing access to a larger patient population.