Infections are the most common presentation of primary immunodeficiency diseases (PIDs). The increase of nucleated red blood cell (NRBC) count is interpreted as a systemic inflammatory response. Platelets play an important role in the pathogenesis of inflammatory disease. The relationship of platelet indices (PIs) and disease activity have been demonstrated in various inflammatory diseases. The aims of this study was to evaluate and compare NRBC and platelet/lymphocyte ratio (PLR), PIs [mean platelet volume (MPV), platelet distribution width (PDW), platelet large cell ratio (PLCR)] with a possible indirect inflammatory marker in children with PIDs. Data were recorded retrospectively from 66 PIDs patients, < 16 years of age. The relationships between peripheral NRBC, C-reactive protein (CRP) and PIs were analyzed. NRBC was positively correlated with CRP (p < 0.037), white blood cells (WBC) (p < 0.020), PLR (p < 0.044), PDW (p < 0.037) and PLCR (p < 0.001) and it was negatively correlated with platelet distribution width (PDW) (p < 0.036) in PIDs patients. A cutoff level of 0.80% NRBC, ≥15.55% PDW, ≥8.65 MPV and ≥43.67 PLR showed the best performance to predict PIDs, with 81% sensitivity, 27% specificity; 61% sensitivity, 37% specificity; 70% sensitivity, 43% specificity; 54% sensitivity, 40% specificity, respectively. Our results suggested that these indices may be used as auxillary diagnostic markers of PIDs with positive NRBC, showing more meaningful results than those known as the traditional infection markers for PIDs prediction. Elevated NRBC and MPV and low PDW are associated with infections and could be helpfull in the early diagnostic susception of PIDs. They can be used as rapidly accessible parameters for awareness of PIDs. These markers are easy to use in daily practice and without extra costs.

Keywords: infection, nucleated red blood cells, platelet indices, platelet-to-lymphocyte ratio, primary immunodeficiency