Patient encounter length of stay (LOS) remains an important measurable factor in evaluating emergency department (ED) performance. Previous studies examined how daily ED volumes, inpatient hospital occupancy, number of elective surgical admissions, and ED physician level of training affect ED throughput. There are limited studies to date that directly examine how ED nursing hours affect ED patient LOS and number of patient that leave without been seen (LWBS) by a provider. We hypothesize that below median nursing hours adversely affected ED LOS metrics: door-to discharge LOS, door-to-admit LOS and number of patient who LWBS. Our hospital is an urban, tertiary care, safety-net hospital with 254 medical/surgical inpatient beds and 80 ED beds. All electronic hospital records of 105,887 ED visits were retrospectively reviewed from January 1, 2015 to December 31, 2015. Daily ED LOS for admitted and discharged patients was recorded as well as daily ED patient volume and number of patients who LWBS each day from the ED. Daily nursing hours were determined from nursing staff records over the same time period. The effect of ED nursing hours on ED metrics was evaluated using analysis of covariance and controlled for total daily ED volume as well as hospital occupancy. Daily nursing hours were reflected in a binary variable that compared days with above-median nursing hour to days with below-median nursing hour days as a fixed factor. ED patients’ daily door to discharge LOS, door to admit LOS, and the rate of LWBS were used as the dependent variable in each model. SPSS Univariate GLM procedure was utilized for all analyses. Controlling for daily ED volume and hospital occupancy, days with below median nursing hours compared to above median nursing hours led to a 19.7-minute increase per patient in door to discharge LOS, F(1, 360) = 24.07, < 0.001. There was also an increase of 7 patients per day who LWBS, F(1, 360) = 80.96, p = < 0.001. Door to admit LOS was not significantly affected by nursing hours, F(1, 359) = 1.52, p = 0.22.Table 1ED LOS for Discharged PtsED LOS for Admitted PtsLWBSDays With Nursing Hours Below-Median259.0 minutes(95% CI 253.9-264.2)463.3 minutes(95% CI 447.8-478.8)21 patients(95% CI 20-22)Days With Nursing Hours Above-Median239.3 minutes(95% CI 234.1-244.6)456.4 minutes(95% CI 445.2-467.7)14 patients(95% CI 13-15)Covariates appearing in the model are evaluated at the following values: Daily ED Volume = 290.3, Hospital Occupancy = 249.7 (98.3%) Open table in a new tab Covariates appearing in the model are evaluated at the following values: Daily ED Volume = 290.3, Hospital Occupancy = 249.7 (98.3%) ED LOS metrics remain an important marker in evaluating ED performance. In this study, nursing hours was identified as a factor, independent of daily ED volume and hospital occupancy, that contributed to ED LOS and number of patients who LWBS. Below median-nursing hours contribute to a statistically significant adverse increase in door-to-discharge LOS and number of patients who LWBS. Such analysis is a pivotal step towards identifying optimal nursing hours and maximizing throughput for our safety net hospital.