Researchers, led by Canan Akkus, investigated the levels of neutrophil-to-lymphocyte (NLR) and platelet-to-lymphocyte (PLR) ratios in patients who experienced a pulmonary embolism (PE) during COVID-19 infection. They found that, while NLR and PLR ratios were higher in PE patients, they could not identify a relationship between NLR and PLR levels and PE development in COVID-19.
Their report, published in the Indian Journal of Critical Care Medicine, highlighted that increased NLR and PLR ratios were poor prognostic indicators in both COVID-19 and PE. Additionally, “NLR and PLR displayed higher values in the COVID-19 cases with the mortal course who were detected to have PE.”
The study was conducted on retrospective records of 1,452 patients with COVID-19, among which 17 (1.2%) were diagnosed with PE. In patients with PE, leukocyte counts (P = 0.001), neutrophil counts (P <0.001), neutrophil percentages, (P = 0.001) NLR (P <0.001), and PLR (P = 0.006) were higher than in controls, while lymphocyte counts (P = 0.004) and lymphocyte percentages (P <0.001) were relatively lower.
Among patients who died, the investigators reported increased leukocyte and neutrophil counts, neutrophil percentages, NLR, and PLR (all P <0.001) compared with surviving patients. Relative to the surviving patients, those who died also had decreased lymphocyte counts and percentages (both P <0.001), hemoglobin (P = 0.005), hematocrit (P = 0.012), and platelet counts (P <0.001).
Notably, while NLR and PLR level cutoffs for predicting PE were found at 4.338 and 187.83, the cutoff values of NLR and PLR for predicting mortality were, respectively, 4.301 and 172.5. Investigators also observed that all hematological parameters had no impact on the development of PE.
The study’s authors closed with the observation that “there is no study evaluating NLR and PLR levels in those with PE developing in the course of COVID-19,” and theorized that their findings will be beneficial to prevent PE or diagnose it before development in patients with COVID-19. They called for larger prospective studies to further examine the increase NLR and PLR ratios in COVID-19 patients with PE.