CAP is believed to be a heterogeneous disorder, either in the range of the causative organisms or in the response of the affected host . Although being an acute illness, CAP is associated with long-term morbidity and mortality even after apparent recovery leading to extra costs and consumption of available resources .
Platelets are well known to play an important role in both the coagulation system and the host defense against different microbial agents. Hence, platelet count might be considered as an additional marker to judge the severity of illness in patients hospitalized with CAP .
In the current study, it was found that the number of CAP patients with thrombocytosis was 33 with a percentage of 13.2%, while, the number of CAP patients with thrombocytopenia was 15 with a percentage of 6% of all hospitalized patients with CAP. This is consistent with the study carried out by Mirsaeidi et al. who showed that 13% of CAP patients presented with thrombocytosis and 5% presented with thrombocytopenia .
In this study, it was found that CAP patients with thrombocytosis were younger with a mean age of 54.2 ± 12.6 years compared to CAP patients with normal platelet count with mean age 59 ± 19 and CAP patients with thrombocytopenia with mean age of 73 ± 9.5. This is consistent with the study by Prina et al. who stated that younger patients are healthier with more strong inflammatory response so there is an increase of the platelet count as a part of the inflammatory response while older patients have more frequent comorbidities and less inflammatory response so there is decreased platelet count .
In this study, the CURB-65 severity score was significantly higher among CAP patients with thrombocytopenia when compared to those patients with normal platelet count or those with thrombocytosis. This could be explained that thrombocytopenia is associated with more severe pneumonia.
In the current study, respiratory complications including pleural effusion, empyema, and lung abscess were significantly higher among patients with thrombocytosis when compared to patients with thrombocytopenia or patients with normal platelet count. This is adherent to other studies by Chalmers et al. and Prina et al. That could be referred to the tendency of compartmentalization of infection with thrombocytosis [5, 14].
Pleural effusion is common among patients with CAP. It may develop in up to 57% of patients hospitalized with pneumonia. Furthermore, pleural effusion is considered to be a marker of pneumonia severity and is linked to an increased risk of treatment failure . Empyema is recognized to be associated with unfavorable outcomes in CAP and is a common etiology of prolonged treatment (either medical or surgical) and hospital stay .
CAP is one of the most common etiologies of severe sepsis and septic shock resulting in up to 45% of cases admitted to hospitals . In this work, it was observed that severe sepsis and septic shock were more common in patients with thrombocytopenia. This is consistent with other studies by Mirsaeidi et al. and Prina et al. That could be attributed to loss of effect of platelets that tend to quarantine the infection resulting in spread of infection with the occurrence of more systemic complications [5, 13].
Thrombocytopenia is frequently encountered in patients admitted to ICU with severe sepsis and septic shock. Patients with thrombocytopenia developed more attacks of life-threatening bleeding, increased occurrence of acute kidney injury, and longer ICU stay. Persistent thrombocytopenia was linked to higher 28-day mortality .
Different mechanisms are implicated in the occurrence of thrombocytopenia in patients with sepsis. In sepsis, platelets are believed to be activated and adhere to the endothelium, leading to their sequestration and destruction. Immune-mediated mechanisms like nonspecific platelet-associated antibodies and cytokine-driven hemophagocytosis of platelets can also contribute to sepsis-induced thrombocytopenia .
In the current study, CAP patients with thrombocytopenia significantly needed mechanical ventilation either invasive or even non-invasive, when compared to CAP patients both with thrombocytosis or with normal platelet count.
CAP patients with acute respiratory failure (ARF) often need non-invasive ventilatory support. Invasive mechanical ventilation is indicated in patients with life-threatening ARF or in those who have failed to respond to non-invasive ventilation (NIV) treatment .
Results of this study showed that CAP patients with thrombocytopenia and CAP patients with thrombocytosis had significant 30 days readmission and significant 30 days mortality when compared to CAP patients with normal platelet count. This could be attributed to more frequent complications and more severe pneumonia among those patient [12, 13].
In the current study, 30 days mortality was independently associated with septic shock, older age more than 65 years, confusion at admission, thrombocytopenia, PaO2/FIO2 < 200 mmHg, and thrombocytosis.
This is consistent with other studies by Laserna et al. and Prina et al. [5, 20].
While thrombocytosis and thrombocytopenia as shown in this study and other studies are important factors in predicting morbidity & mortality in CAP, complications with thrombocytosis were more as local complications in the form of lung abscess, empyema, and pleural effusion while complications with thrombocytopenia were more as general complications in the form of severe sepsis and septic shock. Higher mortality in CAP patients with thrombocytosis could be attributed to insufficient management of the respiratory complications for several causes, e.g., late diagnosis and drainage, inadequate antibiotic, inadequate treatment duration, or absence of adequate follow-up . The prognostic impact of platelets in patients admitted to ICU for severe CAP was demonstrated since the lower was the initial platelet count, the higher was the mortality rate .
This study had the following limitations: first, small number of studied patients; second, causative organisms were not studied to explore their potential relation to platelet count although it showed no significant statistical difference in other studies; third, biomarkers were not analyzed; and finally, we recommend inclusion of thrombocytosis and thrombocytopenia in severity assessment of patients with CAP. Also, further studies on platelet count in CAP patients to evaluate its impact on the outcome are needed.