Introduction Symptoms of COVID-19 vary in severity and presentation. When admitting patients to the hospital, it is desirable to isolate patients with COVID-19 from those without the disease. However, reliably identifying patients with COVID-19 in the emergency department before hospital admission is often limited by the speed and availability of testing. Previous studies determined a low lymphocyte count is commonly found in patients with COVID-19. We sought to explore the sensitivity of absolute lymphocyte count in patients presenting to the emergency department requiring subsequent hospitalization who were found to have COVID-19. Methods A retrospective chart review was performed on 312 patients with laboratory-confirmed COVID-19 who were admitted to the hospital from the emergency department. The absolute lymphocyte count for these patients was used to calculate sensitivities at various cut-off values. The relationships between absolute lymphocyte count and variables, including age, sex, need for intubation, and mortality, were also explored. Results Cut-off values for absolute lymphocyte count ranged from 1.1 K/uL to 2.0 K/uL, with sensitivities of 72% and 94%, respectively. Additionally, lower mean absolute lymphocyte counts were identified in males, patients who required intubation, and patients who died. Conclusion Knowing the sensitivity of absolute lymphocyte count in patients with COVID-19 may help identify patients who are unlikely to have the disease. Additionally, absolute lymphocyte count can be used as a marker of disease severity in patients with COVID-19.

Poly-ADP ribose polymerase 1 (PARP1) is clinically important because of its synthetic lethality with breast cancer allele 1 and 2 mutations, which are causative for inherited breast and ovarian cancers. Biochemically, PARP1 is a single-stranded DNA break repair protein that is needed for preserving genomic integrity. In addition, PARP1 has been implicated in a veritable plethora of additional cellular pathways and thus its precise contribution(s) to human biology has remained obscure. To help address this deficiency, we utilized gene editing to construct genetically-null PARP1 human cancer cells. We found a minor role for PARP1 in an alternative form of DNA double-strand break (DSB) repair, but only when these cells were deficient for the classical form of DSB repair. Despite being proficient for DSB repair, however, cell cycle progression defects and elevated endogenous DNA damage signaling were observed. These deficiencies were instead linked to telomere defects, where PARP1−/− cells had short telomeres that co-localized with markers of endogenous DNA damage and were compromised in their ability to escape a telomere-driven crisis. Our data suggest that while PARP1 does not participate significantly in DNA DSB repair itself, it does prevent the incidence of telomeric DSBs, which, in turn, can drive genomic instability.