Changes in White Blood Cell Count After Steroid Administration in Asthma Patients With and Without Infection

Distinguishing whether leukocytosis reflects a viral or bacterial infection or noninfectious etiology remains a challenge in asthma exacerbations. Systemic corticosteroids, well-recognized to cause leukocytosis, can confound interpretation of white blood cell (WBC) counts, particularly when infection is suspected. We sought to quantify WBC changes following steroid administration in patients hospitalized for asthma exacerbation and to compare these changes among patients with asthma alone, asthma with pneumonia, and asthma with viral respiratory infections.

We conducted a retrospective cohort study of adults presenting to the ED with acute asthma exacerbation between January 1, 2023, and December 31, 2024. Eligible patients had a baseline complete blood count (CBC) prior to steroid administration, received oral or patenteral corticosteroids, and had at least one subsequent CBC during hospitalization. Patients on antibiotics prior to admission, pregnant patients, those requiring ICU care, or those who died during hospitalization were excluded. Changes in WBC over time were analyzed using linear mixed-effects models with random patient intercepts and fixed effects for disease group, time, baseline WBC, age, sex, Charlson Comorbidity Index, and Emergency Severity Index.

Seventy-four patients met inclusion criteria: 44 with asthma alone, 9 with asthma and pneumonia, 19 with asthma and viral infection, and 2 with both pneumonia and viral infection. Compared with asthma alone, patients with asthma and pneumonia had a mean WBC change that was 0.48 K/µL lower (95%CI−4.17 to 3.64). Patients with asthma and viral infection demonstrated a 0.34 K/µL higher change (95%CI−4.13 to 4.57), while those with both pneumonia and viral infection had a 0.83 K/µL lower change (95% CI−10.17 to 7.94). None of these differences were statistically significant.

Among patients hospitalized for asthma exacerbation, steroid-associated leukocytosis did not differ significantly between those with asthma alone and those with concurrent bacterial or viral respiratory infections. These findings suggest that changes in WBC count after steroid administration have limited utility in distinguishing infectious from steroid-related leukocytosis in this population and should be interpreted cautiously when guiding antibiotic decisions.