The Value of the Neutrophil to Lymphocyte Ratio in the Diagnosis of Bacterial Infections
The Value of the Neutrophil to Lymphocyte Ratio in the Diagnosis of Bacterial Infections
The "gold standard" for diagnosing a bacterial infection is isolation of the pathogenic germ, which is not easy in routine clinical practice.
Conventional markers do not have sufficient diagnostic value for making a rapid diagnosis on admission. A 2004 literature calculated the diagnostic values of C-reactive protein (CRP) and procalcitonin (PCT) levels for the diagnosis of bacterial infections, relative to other causes of inflammation. For CRP, the sensitivity was 75% (95% CI: 62%-84%) and the specificity was 67% (95% CI: 56%-77%). For PCT, the sensitivity was 88% (95% CI: 62%-84%) and the specificity was 81% (95% CI: 67%-90%).
The first cellular immune response to infection consists of the mobilization of polynuclear neutrophils from the bone marrow to the infection site under the effect of pre-inflammatory cytokines, as well as the apoptosis of lymphocytes and their sequestration at the infection site. This results in lymphopenia and the elevated polynuclear neutrophil count (PNN) observed in bacterial infections.
Hence, it is legitimate to hypothesize that the neutrophil to lymphocyte ratio (NLR) can be used in the diagnosis of bacterial infection. This ratio's value in the diagnosis of sepsis in the emergency department was studied and the researchers found higher diagnostic values than for CRP and PCT.
The NLR's potential value in the diagnosis of a bacterial infection in a context of fever or hyperthermia (regardless of the presence or absence of bacteraemia) has not been studied before. This ratio could also be compared with standard biomarkers (CRP and PCT levels, the white blood cell count and the PNN).
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