Correctly judging the severity and prognosis of critically ill patients is the core concern of clinicians. Making a more accurate judgment of the severity and development trend of the disease through some indicators is extremely important for adjusting the treatment measures. For critically ill patients with large burns and sepsis, some indicators are considered to be of value in determining the severity and prognosis of the disease, such as monocyte surface human leukocyte antigen-DR (HLA-DR) expression, Th1/Th2 ratio, NK cell function, etc. However, the dynamic monitoring of these indicators is complicated or expensive, and their routine application will certainly cause a waste of medical resources and a significant increase in costs. Therefore, these tests are still only in the laboratory stage and have not been widely used and confirmed in clinical practice. In contrast, platelets, a simple and easy-to-measure indicator, have become a common indicator for clinicians to determine the condition of the disease, and a sustained and significant decrease in its count is a typical sign of a dangerous condition and has early warning significance. As an early warning indicator, the specificity and sensitivity of platelet count has not been compared with other indicators, but it is undeniable that the ease of obtaining platelet count and the simplicity of interpreting the test results are unparalleled by most other indicators. Sepsis is the leading cause of death in patients with massive burns. Abnormal immune function is currently considered to be one of the major causes of sepsis. Therefore, it would be more straightforward to judge the progress and prognosis of the disease by indicators reflecting immune function than by platelets – an indirect indicator of the severity of sepsis through damage to the hematopoietic and coagulation systems. In clinical practice, the indicators for evaluating immune function are lacking, and the strength of immune function is difficult to be discerned by general clinical indicators, while the detection of HLA-DR and Th1/Th2 ratio is difficult to be promoted, and even the simpler and easier T-lymphocyte subpopulation analysis is difficult to be carried out in most primary hospitals. In this study, we found that patients who died of sepsis had significantly lower lymphocyte counts, which were very similar and synchronous with the lower platelet counts; in some cases, the lower lymphocyte counts preceded the lower platelet counts; and statistical analysis showed that the relative risk of death in those with significantly lower lymphocyte counts was 2.25 times higher than that in those with normal lymphocyte counts. These results suggest that a decrease in lymphocyte count, similar to a decrease in platelet count, is one of the signs of critical illness and is a marker of poor prognosis. The present study was taken from patients with critical burns, and similar conditions to the present study have been observed in patients with other severe infections: in 1998, it was reported that peripheral blood lymphocyte counts were significantly lower in patients in the death group of pulmonary infections than in the surviving group; based on monitoring of 135 patients with critical SIRS, it was found that platelets and lymphocytes were lower in the death group than in the surviving group at all time points, and that platelet and lymphocyte counts in the death group In patients with severe acute respiratory syndrome (SARS), the lymphocyte count in the critically ill patients was significantly lower than that in the mildly ill patients, and was lowest in the most severe stage of the disease, so the reduced lymphocyte count was included as one of the diagnostic criteria of SARS. It has been shown that there is a linear positive correlation between CD4+ T lymphocyte count and total lymphocyte count in healthy adults, and the value of CD4+ T lymphocytes can be inferred from total lymphocyte count; while T lymphocyte subpopulation analysis showed that decreased CD4+ T lymphocytes were the main change in the composition of lymphocyte subpopulation in critically ill burn patients. It can be inferred that the decrease in lymphocyte counts observed in this study reflects a decrease in CD4+ T lymphocytes. hotchkiss et al. reported a significant decrease in lymphocytes in those who died of sepsis, a significant increase in lymphocyte apoptosis in the spleen and lymph nodes, and the apoptotic cells were dominated by CD4+ T cells, B cells and dendritic cells; in severe sepsis, CD4+ T cells and The absence of CD4+ T cells and dendritic cells would be catastrophic in severe sepsis, because the loss of B cells, CD4+ T cells and dendritic cells signals the loss of antibody production, macrophage activation and antigen presentation. In sepsis, the body is immunosuppressed, such as loss of delayed hypersensitivity, reduced pathogen clearance, and susceptibility to infection, etc. The decrease in lymphocyte count due to massive lymphocyte apoptosis is an important cause of these manifestations, and inhibition of lymphocyte apoptosis can help improve the body’s immune function and thus increase survival. The main pathways of lymphocyte apoptosis have been recognized, but based on the complexity of apoptosis, there is still a long way to go to obtain effective therapeutic means to inhibit its excessive apoptosis, and the ultimate solution may be to investigate the mechanisms leading to lymphocyte apoptosis in sepsis at the signal transduction level, to find specific signaling pathways and/or targets, and to inhibit excessive lymphocyte apoptosis in order to improve immune function and The results of the present study suggest that sepsis can be treated with the best possible treatment. In conclusion, the results of this study showed that the lymphocyte count in critically ill burn patients who died of sepsis was significantly reduced, which can be used as a simple and effective indication to reflect the criticality of the disease and judge the prognosis in combination with the reduction of platelet count; however, it is not clear how the lymphocyte count changes in different stages of the disease and its correlation with the criticality of the disease in patients who died and survived sepsis, and even how the application of immunomodulators such as thymidine affects the lymphocyte count. The effect of immunomodulators such as thymidine on lymphocyte count is yet to be studied in a large sample.