['This study sought to determine if the automated absolute lymphocyte count (ALC) predicts a "low" (<200 × 10(6) cells/μL) CD4 count in patients with known human immunodeficiency virus (HIV+) who are admitted to the hospital from the emergency department (ED).', 'This retrospective cohort study over an 8-year period was performed in a single, urban academic tertiary care hospital with over 85,000 annual ED visits. Included were patients who were known to be HIV+ and admitted from the ED, who had an ALC measured in the ED and a CD4 count measured within 24 hours of admission. Back-translated means and confidence intervals (CIs) were used to describe CD4 and ALC levels. The primary outcome was to determine the utility of an ALC threshold for predicting a CD4 count of <200 × 10(6) cells/μL by assessing the strength of association between log-transformed ALC and CD4 counts using a Pearson correlation coefficient. In addition, area under the receiver operator curve (AUC) and a decision plot analysis were used to calculate the sensitivity, specificity, and the positive and negative likelihood ratios to identify prespecified optimal clinical thresholds of a likelihood ratio of <0.1 and >10.', '\u2002 A total of 866 patients (mean age 42 years, 40% female) met inclusion criteria. The transformed means (95% CIs) for CD4 and ALC were 34 (31-38) and 654 (618-691), respectively. There was a significant relationship between the two measures, r = 0.74 (95% CI = 0.71 to 0.77, p < 0.01). The AUC was 0.92 (95% CI = 0.90 to 0.94, p < 0.001). An ALC of <1700 × 10(6) cells/μL had a sensitivity of 95% (95% CI = 93% to 96%), specificity of 52% (95% CI = 43% to 62%), and negative likelihood ratio of 0.09 (95% CI = 0.05 to 0.2) for a CD4 count of <200 × 10(6) cells/μL. An ALC of <950 × 10(6) cells/μL has a sensitivity of 76% (95% CI = 73% to 79%), specificity of 93% (95% CI = 87% to 96%), and positive likelihood ratio of 10.1 (95% CI = 8.2 to 14) for a CD4 count of <200 × 10(6) cells/μL.'] Does absolute lymphocyte count in the emergency department predict a low CD4 count in admitted HIV-positive patients?