Association Between Absolute Lymphocyte Count And Severity Of Covid-19: A Retrospective Cross-Sectional Study.

Abstract

Background: Lymphopenia is a frequently reported hematological abnormality in coronavirus disease 2019 (COVID-19) and has been associated with severe illness. Absolute lymphocyte count (ALC), being routinely available from a complete blood count, may provide an inexpensive marker for assessing disease severity, particularly in resource-constrained settings. Objectives: To estimate ALC among hospitalized patients with COVID-19 and determine its association with disease severity. Serum ferritin levels were additionally evaluated. Materials and Methods: This retrospective cross-sectional study included 200 adult patients with RT-PCR-confirmed COVID-19 admitted to Government Medical College, Thiruvananthapuram. Patients were classified into severity categories A, B, and C according to the prevailing state guidelines. Demographic characteristics, comorbidities, ALC, serum ferritin, and other hematological parameters were obtained from medical records. Quantitative variables were compared using one-way analysis of variance, followed by Tukey post-hoc testing where applicable. Categorical associations were evaluated using the chi-square test. A P value <0.05 was considered statistically significant. Results: Of 200 patients, 20 (10.0%) belonged to category A, 99 (49.5%) to category B, and 81 (40.5%) to category C. Mean ALC declined progressively from 1990.74 ± 620.78 cells/µL in category A to 1120.09 ± 624.37 cells/µL in category B and 780.45 ± 305.85 cells/µL in category C (F[2,197]=44.585, P<0.001). Mean serum ferritin increased from 134.34 ± 224.90 ng/mL in category A to 539.84 ± 623.02 ng/mL in category C (F=11.357, P<0.001). ANC, NLR, and ESR also increased significantly with severity, whereas hemoglobin did not. Conclusion: ALC showed a significant inverse association with COVID-19 severity. Its routine availability, rapid turnaround, and low cost support its potential utility as a simple severity-associated laboratory marker in hospitalized COVID-19 patients.