A Comparative Study Between Neutrophil/Lymphocyte Ratio and Lactate/Albumin Ratio as Predictive Inflammatory Markers for Sepsis in Patients With Lower Respiratory Tract Infection in ICU

Lower respiratory tract infection (LRTI) is one of the most common infectious diseases that lead to admission of patients to ICU. It includes a wide range of respiratory infections; such as pneumonia, bronchitis, empyema and lung abscess. Furthermore, it is associated with considerable morbidity and mortality. Because delay in the ICU admission of patients with LRTI has been shown to be associated with increased mortality, it can be helpful to predict the mortality of LRTI patients in hospitals.

Sepsis is a life-threatening medical emergency induced by uncontrolled systemic inflammatory response of the host to infection. Without an early and aggressive management, sepsis can rapidly lead to organ failure, tissue hypoperfusion, and death. Bacterial infections cause most cases of sepsis, but it can also be a result of other infections; such as viral, fungal or parasitic infections. Sepsis-3 definitions for sepsis management were established in 2016 according to the Surviving Sepsis Campaign guidelines. They define sepsis as "a life-threatening organ dysfunction caused by a dysregulated host response to infection", and septic shock as "a subset of sepsis in which underling circulatory and cellular/metabolic abnormalities are profound enough to substantially increase mortality".

According to Sepsis-3 criteria, sepsis and septic shock are currently diagnosed as follows: sepsis-suspected or documented infection plus SOFA (Sequential Organ Failure Assessment) score ≥2; septic shock-sepsis plus vasopressor therapy needed to maintain mean arterial pressure (MAP) ≥65 mmHg plus lactate ≥2 mmol/L (18 mg/L) despite adequate fluid resuscitation. However these diagnosis criteria, the early evaluation of sepsis severity and prognosis is still imprecise and significant research is being performed to address this issue.

The neutrophil/lymphocyte ratio (NLR) was studied in order to provide an easier way to diagnose sepsis. This ratio can be calculated both from the absolute number of neutrophils and lymphocytes, and from their relative number. The importance of this report derives from the fact that physiological stress causes an increase in the number of neutrophils and a decrease in the number of lymphocytes. Sepsis stimulates lymphocyte apoptosis, so this ratio is increased in these cases. Septic shock causes a dramatic decrease in lymphocyte count, so the NLR ratio increases significantly.

Increased lactate production is a prognostic marker of generalized hypoxia in distributive shock. Previous studies have reported that lactate levels are a dependable parameter in diagnosis, therapeutic evaluation, and prognosis in circulatory shock. Increased lactate levels are used worldwide for early diagnosis, management, and in risk stratification of patients with septic shock .