to detect the SARS-CoV-2 virus or had been diagnosed in the community, were over the age of 18, and were admitted and discharged from the hospital between 03/01/2020 and 05/07/2020. Data were collected and extracted from an electronic medical record system and included many variables, such as demographic, clinical outcomes, and laboratory data. We define severe disease as those patients who required admission to the ICU; non-severe disease is classified as those admitted to the hospital, but did not require ICU admission.
Admission to the ICU was determined by clinical factors, namely respiratory failure and hemodynamic instability. Lymphocytopenia was not part of these criteria. Acute Kidney Injury (AKI) is defined as a rise in serum creatinine > 0.3 mg/dL from baseline within 48 hours at any time during admission (if baseline data were unavailable, the lowest value during admission was presumed to be the baseline; if only one value was available, the patient was not presumed to have an AKI).
All laboratory data were collected within 24 hours of admission.
Laboratory data were analyzed by our hospital's hematology laboratory. All laboratory samples are typically processed within hour of receipt. Complete blood counts (CBCs) were measured on automated CBC and differential analyzer (X-N 3000), if the XN3000 could not classify a WBC an attached module (SP10) automatically made the blood smear slides. This blood smear side was manually loaded onto a cell locator imaging (DM96). Technician classified WBC with differential, if technician had difficulty in interpreting results; the pathologist reviewed the slide. Quality control materials were run every 8 hours. Lymphocytopenia is defined as an absolute lymphocyte count (ALC) < 1.0 × 10 3 cells/µL. Anemia is defined as hemoglobin < 14 gm/dL for men or < 12 gm/dL for women.
Thrombocytopenia is defined as platelet count < 150.0 × 10 3 cells/ µL. Leukopenia is defined as leukocyte count < 4.4 × 10 3 cells/µL. Leukocytosis is defined as a leukocyte count > 11.0 × 10 3 cells/µL. analyses, a P-value < .05 was used to reject the null hypothesis that either there was no difference between two samples tested or that samples were independent. Odds ratios and confidence intervals were calculated using the package epiR 9 in the R-studio software.
Code is available upon request. Figures were prepared using the gg-plot2 10 software in the R software platform.
We obtained a cohort of 57 patients who were admitted to and discharged from the hospital between 03/01/2020 and 05/01/2020.
The cohort was predominantly male (59%), obese (average BMI of 32.3 ± 1.19 kg/m 2 ) with an average age of 58.2 ± 2.08 years. Our cohort consisted mostly of patients with minority backgrounds (86%). Thirty-one percent of patients (N = 18) were admitted to the ICU and mortality was 16% (N = 9). Of note, two patients had a diagnosis of Human Immunodeficiency Virus (HIV) infection.
The median Charlson comorbidity index was 4 (1.5-6), indicating an median 10-year survival rate of 53%. 11 In our study, we found that 50% (9/18) of patients admitted to the ICU required intubation and 38% (7/18) required vasopressors (Table 3) . Thus, patients admitted to the ICU were classified as having severe disease given the relatively common occurrence of hemodynamic instability and respiratory failure in this population.
The average ALC count obtained at the time of admission to the hospital in patients requiring ICU admission was lower (0.8 ± 0.11 × 10 3 cells/µL) relative to those not needing ICU admission (1.4 ± 0.15 × 10 3 cells/µL; P = .01; Table 1, Figure 1 ). Additionally, more patients admitted to the ICU had lymphocytopenia (62%) at the time of admission to the hospital compared to those not admitted to the ICU (32%; P = .04; Table 2 
We found that patients admitted to the ICU were more likely to have anemia (78% of ICU patients versus 49% of non-ICU patients, P = .04; Table 2 ) than those that were not and there was a nonsignificant trend toward a lower hemoglobin concentration in ICU patients (Table 1) . Additionally, platelet count was found to be higher in patients admitted to the ICU versus those who were not (P = .02, 
Although lymphocytopenia was not seen to be associated with mortality in this study, the finding of an association with AKI warrants further research. Nevertheless, it is apparent here that lymphocytopenia may serve as a prognostic marker for AKI in Covid-19 patients.
Finally, although lymphocytopenia was not found to be statistically related to other clinical outcomes, such as mortality and need for intubation, the trend was largely in favor of a correlation; our sample size was likely small to demonstrate this association. Indeed, mortality is higher in patients with lower lymphocyte counts, 16 thus confirming the trends observed here. Future studies should address ICU outcomes such as the need for intubation based on lymphocytopenia with appropriate statistical power to validate these findings.
The limitations of this study include smaller sample size and focus on one community hospital. Additionally, other leukocyte subtypes such as eosinophil and neutrophil counts were not examined in this study. The strengths of this study include the use of an easily obtained laboratory value that is associated with clinical outcomes and a focus on a predominantly minority population of patients who seem to be heavily impacted by Covid-19. In summary, we find that lymphocytopenia and anemia are more common in patients admitted to the ICU, with an odds ratio of approximately 3.4 and 3.6, respectively. Additionally, patients with lymphocytopenia are more likely to develop an AKI relative to those without lymphocytopenia by an odds ratio of 4.2. Thus, it appears likely that lymphocytopenia is related to disease severity and clinical outcomes in Covid-19.
None declared for JW, AD, SL, AF, and BC.
JW and AF were involved in planning the study and collected data.
JW, AD, SL, BC, and AF performed data analysis and wrote the manuscript. All authors have approved of the final draft.
Ahmad Farooq https://orcid.org/0000-0002-3477-0404