From the Guidelines
COVID-19 typically causes leukopenia, particularly lymphopenia, rather than leukocytosis, as evidenced by the disease's impact on the immune system and inflammatory response 1. When considering the effects of COVID-19 on white blood cell counts, it's essential to understand the disease's progression and the body's response to the infection. The virus's impact on the immune system, including the reduction of lymphocytes, is a key aspect of its pathology.
Key Points to Consider
- Most viral infections, including COVID-19, tend to decrease the total white blood cell count, particularly affecting lymphocytes (lymphopenia) 1.
- Leukocytosis may occur in severe cases of COVID-19, especially if there is a secondary bacterial infection or as part of an inflammatory response, such as a cytokine storm 1.
- The virus primarily affects the respiratory system by binding to ACE2 receptors on cells, leading to infection and inflammation, which can influence white blood cell counts 1.
- Monitoring a COVID-19 patient's complete blood count (CBC) is crucial to track white blood cell counts and differentials, helping clinicians distinguish between viral and bacterial causes and guide appropriate treatment decisions 1.
Clinical Implications
In clinical practice, understanding the patterns of white blood cell counts in COVID-19 patients is vital for making informed treatment decisions.
- If leukocytosis is observed in a COVID-19 patient, it may indicate disease progression, a cytokine storm, or a secondary bacterial infection that might require additional treatment such as antibiotics 1.
- Clinicians should be aware of these potential complications and adjust their treatment strategies accordingly, prioritizing the patient's morbidity, mortality, and quality of life outcomes.
From the Research
Leukocytosis in COVID-19
- Leukocytosis, an increase in white blood cell count, has been observed in some COVID-19 patients, particularly those with severe infections 2, 3, 4.
- A study published in 2020 found that leukocytosis was associated with poor outcomes in COVID-19 patients, with an odds ratio of 4.51 (95% CI 2.53-8.04) 2.
- Another study published in 2023 found that leukocytosis was a strong predictor of COVID-19 severity, with a crude odds ratio of 3.866 (95% CI 1.815-8.236) 3.
- However, some studies have also reported leukopenia, a decrease in white blood cell count, in COVID-19 patients, particularly those with mild or asymptomatic infections 5, 3, 4.
Viral Load and Inflammation
- The viral load and level of systemic inflammation have been found to affect the severity of COVID-19 and the response to treatment 6.
- A study published in 2022 found that remdesivir decreased the risk of mortality and need for invasive mechanical ventilation in hospitalized COVID-19 patients with high viral loads and low-grade systemic inflammation 6.
- The study found that the benefits of remdesivir differed depending on the cycle threshold (Ct) values and C-reactive protein (CRP) levels, with the greatest benefit seen in patients with Ct <25 and CRP <38 mg/L 6.
Laboratory Findings
- Laboratory findings, including white blood cell count, neutrophil count, monocyte count, basophil count, and neutrophil to lymphocyte ratio, have been found to differ between COVID-19 patients with mild or asymptomatic infections and those with moderate or severe infections 4.
- A study published in 2021 found that COVID-19 may affect the count of some leukocytes in patients with severe infection, with significant differences in white blood cell count, neutrophils count, monocytes count, basophils count, and neutrophil to lymphocyte ratio between patients with mild or asymptomatic infections and those with moderate or severe infections 4.