The coronavirus disease 2019 (COVID-19) virus had a devastating experience since its inception. Coronavirus infections lead to severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome in humans. Unlike other viral diseases, COVID-19 has significantly affected both biochemical and hematological values. The world has been witnessing multiple ongoing waves of the COVID-19 pandemic, and its complications have been reported globally in the world including the need for intensive care unit (ICU) admission and mortality in a huge number of cases.
The infection leads to a mild disease in the majority of the patients, whereas others can have severe morbidity and mortality.[3,4] The classification of disease into mild, moderate, and severe cases is important to guide the proper management and prognosis of the patient.[3,4] The analysis of routine hematological laboratory parameters could be helpful in classifying mild, moderate, and severe cases and thus help in predicting the patient’s outcome.[5,6] During the initial first week of the disease, when patients generally have nonspecific symptoms, the white blood cell (WBC) counts and the absolute lymphocyte (LYM) counts are normal or slightly reduced. Between the 7th and 14th day of infection, from the onset of the initial symptoms, there is a rapid surge in the symptoms of the disease. This is with the rise of inflammatory mediators and cytokines, which can even lead to “cytokine storm” with characteristic significant lymphopenia. This happens because LYMs express angiotensin converting enzyme 2 receptor on their surface and it is possible that SARS‐CoV‐2 virus may directly infect the LYMs, causing their lysis and subsequent inflammation.[10,11] This finding was more evident in deceased individuals due to the COVID-19 infection compared to those who survived. Therefore, these parameters are of significant value and are important for the stratification of patients into mild, moderate, and severe cases. The study aims to observe and highlight the changes in the hematological parameters and their prognostic value on COVID-19 hospitalized patients. Hence, we raise the following doubts: Does any of the hematologic parameters have a relevant prognostic value. Could any of the hematological parameters be used as biomarkers of prognosis? Is there a pattern of hematological changes during hospital stay associated with increased hospital and intensive admission and stay?
Materials and Methods
A retrospective study was conducted at a tertiary care hospital for nine months from March 1, 2020 to November 30, 2020.
The patients with confirmed reverse transcriptase-polymerase chain reaction COVID-19 patients between 18 and 70 years of age admitted to ICU and non-ICU wards were included in the study.
There were 150 cases consisting of 96 male patients and 54 female patients. The patients were divided into subgroups depending on the severity of infection (ICU vs. non-ICU) and their outcome (survivor vs. non-survivor). There were a total of 62 COVID-19 positive patients admitted to the ICU compared with 88 non-ICU patients. The patients were divided into three groups [Table 1]: recovered ICU patients (n = 50), recovered non-ICU patients (n = 82), deceased from both the groups [n= 18 (ICU = 12 and non-ICU = 6)].
The patients with COVID-19 reverse transcriptase-polymerase chain reaction negative infection or suffering from one or more comorbidities were excluded from the study. The patients with less than three routine blood examinations were also excluded because of a short stay in the hospital.
Data comprising of complete clinical workup, physical examination, and the differential hematological parameters of confirmed reverse transcriptase-polymerase chain reaction positive COVID-19 patients were retrieved from the records at the Departments of Pathology and Critical Care Medicine and medical record section throughout admission was considered the first sample for the study of hematological parameters. If not available, the first sent sample to the lab was considered as the day 1 sample. Only three samples were collected on different days of admission, preferably, day 1, day 5, and day 7. The hematological parameters evaluated were leukocyte count (LEU, 10/µL), neutrophil count (NEU, %), lymphocyte count (%), eosinophil count (EO, %), monocyte count (MONO, %), hemoglobin concentration (Hb, g/dL), platelet count (PLT, 10/µL), red cell distribution width (RDW), and neutrophil–lymphocyte ratio (NLR). The data were compiled and analyzed by the investigators. Results were checked by two co-investigators in a blindfolded manner and were finally analyzed and vetted by the principal investigator. Statistical analysis was done for the data collected from the department. For each parameter, median values corresponded to 95% confidence intervals. 95% were calculated based on the values of parameters from all patients. Mann–Whitney test was applied to compare the data between the described groups, and statistical analysis of the data was done using Statistical Package for Social Sciences (manufacturer IBM, Chicago (Ils), USA) version 22.0 and a P value of 0.05 was considered statistically significant.
The study was performed with the data compiled from the Departments of Pathology and Critical Care Medicine at a tertiary care hospital for 9 months. The patients were aged between 18 and 70 years who were admitted to ICU and non-ICU wards with COVID-19 infection. There was no significant difference in male-to-female ratio in survivors compared to non-survivors in ICU and non-ICU, respectively (76/24 vs. 11/7, respectively, P ≥ 0.05).
There were 82 non-ICU recovered patients, 50 ICU-recovered patients, and 18 patients who died during hospitalization. Table 2 and Figure 1 shows the differences in median values of hematology parameters between COVID-19 patients in non-ICU and ICU departments based on values from all patients analyzed after admission. There were significant differences in the routine laboratory hematological parameters between the above segregated groups. The WBC count and the NEU counts were high in both groups. Patients admitted to ICU had a higher WBC count (P < 0.0001), a higher NEU count with a mean of 9200 mm3/L in non-ICU compared to 15,000 in ICU patients (P < 0.0001) a higher NLR ratio (5.3 in non-ICU and 7.08 in ICU patients with P < 0.05 and a lower LYM count of 15% in non-ICU and 12% in ICU (P < 0.05). There were no significant differences in Hb and EO count (P > 0.05). PLT counts in both groups remained within normal reference values. There was a slight decrease in Hb concentration in both groups but it was non-significant. P-values of differences in LYM count between these two groups were significant.
There were 150 patients included in the study consisting of 96 male patients and 54 female patients, respectively. There was no significant difference between the male-to-female ratio in survivors and deceased patients.[12-14] Wu et al. and others observed that the male sex and older age are associated risk factors for early hospital admission and death. Mousavi et al. observed that the mean age of non- survivors was higher than the survivor, and in ICU was higher than non-ICU. We found that the mean age of patients in the ICU was 50.44 and in non-ICU was 49.46
WBC count and neutrophil count
It was observed in this study that there was increased total leucocyte count and NEU counts in ICU patients compared to non-ICU patients. The NLR was also high among ICU patients and the difference was statistically significant. This could be due to superimposed bacterial infections, which could lead to an increase in LEU and NEU count.[2,16,17] Blomme et al. also observed that the total leucocyte count and NEU count were significantly higher in the deceased COVID-19 patients compared to the recovered COVID-19 patients. They also found that the increased risk of acute respiratory distress syndrome (ARDS) was significantly associated with neutrophilic leucocytosis (P < 0.001) and lymphopenia (P < 0.001).
A retrospective study from China on 187 COVID‐19 patients found that patients with high troponin‐T levels had leukocytosis (P < 0.001), increased NEUs (P < 0.001), and decreased LYM counts (P = 0.01). Urbano et al. Observed that only 4.7% (n = 13) were admitted to the ICU and the overall deceased were 15.4% (n = 2). There were significantly lower values for PLT counts, Hb concentration and MCHaC and significantly higher values were found for the LEU count, NEU/LEU ratio and lactate dehydrogenase. They concluded that age, sex, LYMs, NEUs, NLR, PLTs, erythrocyte count, and mean corpuscular haemoglobin concentration at hospital admission are independent variables for the prognosis of COVID-19 infection They also hypothesized that patients with LEU elevation, NEU elevation, LYM decrease, or PLT count increase and decreased level of erythrocytes, and Hb are more likely to end up in the ICU.
Mousavi et al. observed lymphopenia and neutrophilia in 52.7% and 21.4% of patients, respectively, at the time of admission. They also found that the NEU count was significantly higher in the deceased at the time of admission (P = 0.032). The NLR was within normal limits lying between 1 and 3 in 28.6% of patients. Raised NLR was significantly associated with increased mortality (P = 0.004 and P < 0.001, respectively). Elevated NLR was associated with ICU admission (P = 0.012).
It was also observed in another study raised WBC counts and increased NLR could be used for predicting mortality in COVID-19 patients. Yang et al. observed that elevated NLR can be used as an independent biomarker for assessing poor clinical outcomes in COVID-19 patients. Elshazli et al. performed a systematic review till April 22, 2020 with 52 articles and 6320 laboratory-confirmed COVID-19 cohorts included. The comparison of severe versus mild disease, ICU versus ward admission, and expired versus survivors was performed for 36 laboratory parameters. The mean and 95% confidence intervals (CI) were calculated. They found that increased white blood cells (OR = 1.75) and NEU count (OR = 2.62) have higher odds of progression to severe cases. Similarly, ICU patients had higher levels of WBCs (OR = 5.21), NEUs (OR =6.25), and prolonged PT (OR = 2.18). Patients with high IL-6 (OR = 13.87), CRP (OR =7.09), D-dimer (OR = 6.36), and NEUs (OR = 6.25) had the maximum incidence of mortality. They concluded that numerous hematological parameters mainly NEU count and immunological markers, aid in deciding the prognosis and should be included in evaluating risk stratification and effective management.
Lymphopenia as observed in this study, which was significant in ICU patients compared to non-ICU count was significantly lower in the deceased group compared to recovered patients. They also found that the median LYM count was less in the deceased population but it rose to normal in the patients who were recovering from the disease. They reported a significant difference in LYM count between the ICU, non-ICU, and deceased COVID-19 groups. They also stated that patients with a LYM count of more than 10% over the period had a significantly better chance of recovery than patients with LYMs of less than 10% LYMs have a major role in maintaining the immune status and eliciting an inflammatory response.[17,23-25] In the viral infection, there is a decrease in LYM count which makes the body vulnerable to other superadded bacterial infections.[3,4,26,27] LYMs count has a strong association in COVID-19 patients.[11,28,29]
Fan et al. also found that COVID-19 patients requiring ICU support had significantly lower LYM levels (P < 0.001) at the baseline level during admission. Lymphopenia was also found in another study in China in 85% of patients. Guan et al. observed 1099 COVID‐19 patients during the first 2 months of the COVID-19 epidemic in China. They observed that on admission, the majority of the patients presented with lymphocytopenia (83.2%), 36.2% had thrombocytopenia, and 33.7% were having leukopenia. These parameters were more prominent among severe versus non‐severe cases (96.1% vs. 80.4% for lymphocytopenia, 61.1% vs. 28.1% for leukopenia, and 57.7% vs. 31.6% for thrombocytopenia). This was also reported by other studies in China which included 41, 99, 138 and 201 cases of COVID‐19, respectively.[3,29,30] Lymphopenia is associated with a worse outcome and the need for ICU care, ARDS, and longer hospital stay.[9,29] Similarly, neutrophilia has also been associated with an increased risk of death. Huang et al. and Wang et al. observed an association between lymphopenia and the need for ICU care. Wu et al. found an association between lymphopenia and ARDS development.
There was reduced EO count in both the ICU as well as non-ICU patients, but the difference between the two groups was not statistically significant. Eosinopenia has been observed in the majority of COVID-19 patients.[22,31] EO counts were significantly lower in deceased patients compared to recovered ICU patients as observed by Blomme et al. that there was a low EO count during admission to the hospital and it remained low during the disease and later gradually increased in all COVID-19 groups. Although low EO counts are difficult to monitor due to an already low normal reference value and are difficult to correlate its value and the outcome of COVID-19 disease. A delay in the recovery of EO count toward normal can predict an increased risk of severe progression of COVID-19 disease.
The MONO count observed in this study was within normal limits in both the ICU as well as non-ICU. There was no significant difference in the MONO number between both groups. Similarly, Bloome et al. found that were only slight reduction in the MONO count in COVID-19 patients. The MONO counts were on the lower side in the deceased group compared to the recovered group but were still in the normal reference ranges (2%–10%). In a meta-analysis by Ghahramani et al., they observed a decrease in MONO count along with reduced Hb, PLT, LYM, EO, albumin, serum sodium, LYM to C-reactive protein ratio (LCR), LEU to C-reactive protein ratio, LEU to IL-6 ratio, and an increase in the NEU.
There was thrombocytopenia seen in patients admitted to ICU compared to non-ICU in this study but the mean PLT value was within the normal range and the difference was not statistically significant. Thrombocytopenia is seen in severe cases of COVID-19 infection.[25,26] There is a risk of developing coagulopathies which can eventually lead to multi-organ damage. Thrombocytopenia is multifactorial. The production of PLT may be affected by the direct effect of the virus or due to bone marrow impairment. There can be fragmentation of megakaryocytes due to damage caused to the lung and pulmonary capillary bed due to COVID-19 infection. Stimulation of anti-PLT autoantibodies by SARS-CoV‐2 also triggers immune-mediated PLT destruction. Multi-organ failure may also exacerbate thrombocytopenia.[33,34]
Dysfunctional PLTs might also lead to increased bleeding despite PLT count being in the normal range. It can also occur through the use of antivirals, antibiotics, heparin, and other commonly used agents, as well as hemodialysis and extracorporeal membrane oxygenation. Lupi et al. and others observed that thrombocytopenia was seen in patients infected by COVID-19 patients. Unlike these findings, Blomme et al. did not observe any association between thrombocytopenia and severity or mortality in COVID-19 patients was seen in approximately 36% of COVID-19 hospitalized patients in one study. The study performed by Blomme et al. also found thrombocytopenia in up to 57% of deceased patients. Mousavi et al. observed that the PLTs count was lower than normal. Platelet-to-lymphocyte ratio (PLR) also correlated with mortality and was significantly higher in deceased than recovered patients (299 vs. 203, respectively, P = 0.034). Thrombocytopenia and lower PLT counts were more observed in non-survivors.
A meta‐analysis was performed on nine studies and suggested that thrombocytopenia is significantly associated with the severity of the COVID‐19 infection, especially in the deceased patient, although there is a huge heterogeneity in the data. Qu et al. reported in 30 hospitalized patients that those with thrombocytosis during the disease course had worse outcomes. They also found that the PLR at the time of PLT peak can act as an independent prognostic factor for prolonged hospitalization. Thrombocytopenia is associated with the severity of the disease. Others observed that significantly elevated PLTs had longer average hospitalization stays. This could be because there is a correlation between the PLT count and the SARS-CoV‐2-associated cytokine storm, as the IL-6 promotes megakaryocyte production, by stimulating thyroid peroxidase levels. PLR at the time of the PLT peak (especially during the cytokine storm) is observed as an independent prognostic factor for the more prolonged hospitalization.
There was anemia in patients admitted due to COVID-19 infection. We found reduced Hb in ICU patients compared to non-ICU but the difference was not statistically significant. An increase in the inflammatory cytokines may reduce erythropoiesis and increase red blood cell damage leading to anemia.[22,29] Mousavi et al. found that Hb concentration was lower than 12 gm/dL in 42.4% of patients and low Hb significantly correlated with mortality and ICU admission (P = 0.04). In a meta-analysis, Lippi and Mattiuzzi stated that Hb values are significantly reduced in COVID-19 patients with severe disease, compared to those with milder forms. Blomme et al. also observed that there was a decrease in Hb in all the groups of patients classified into ICU, non-ICU, and deceased patients, suggesting that there was a direct cytopathic effect of the COVID-19 virus on RBCs although it was not significant. They found that there was reduced Hb in patients infected by COVID-19 compared to the other non-COVID-19 influenza viruses, suggesting that the SARS-CoV‐2 virus has a greater effect on RBCs as compared to other viruses like the Influenza virus.[14,36]
Red cell distribution width
There is growing evidence to suggest that elevated red cell distribution width (RDW) can be a predictor of mortality in patients with COVID-19, particularly those who are not admitted to the ICU. RDW is a measure of the variability in the size of red blood cells, and it is often included as part of a standard blood test. Several studies have reported an association between elevated RDW and mortality in COVID-19 patients. For example, a study published in the Journal of Medical Virology in September 2020 found that elevated RDW was a significant predictor of mortality in patients with COVID-19 who were not admitted to the ICU. RDW was associated with an increased risk of death in COVID-19 patients, even after adjusting for other risk factors. While the exact mechanisms underlying the association between elevated RDW and mortality in COVID-19 patients are not yet fully understood, it is thought that elevated RDW may reflect underlying inflammation, oxidative stress, and impaired immune function, all of which can contribute to the severity of COVID-19.
There were a few limitations in this study. The sample size is small to generalize our findings to the general population. Age and comorbidities including hypertension, diabetes, etc., were not taken into account to compare the difference in the result of these hematological parameters on patient outcomes.
This study was performed to see the changes in the hematological parameters and its association with the clinical severity of the disease was also observed. The routine hematological lab parameters were compared between severe and mild (ICU vs. non-ICU) COVID-19 patients. Most of these parameters were significantly different in ICU, non-ICU, and deceased COVID-19 groups compared to recovered COVID-19 patients of which the increase in WBC count, NEUs, NLR, and a decrease in LYMs were the most significant findings. The EOs and PLT count appeared to be low in all COVID-19 patients, and thus there was no significant difference between these two groups.
Thus, an attempt has been made to observe the changes in the hematological parameter with COVID-19 and to see whether these variations can be used for prognosis and to notify the severity of the disease.
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Conflicts of interest
There are no conflicts of interest.
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