Infection‑Driven Leukocytosis in Systemic Lupus Erythematosus

Epidemiology and Clinical Priority

• In patients with systemic lupus erythematosus, infection is the predominant cause of an elevated white‑blood‑cell count and represents a critical diagnostic priority because infections are among the leading contributors to morbidity and mortality in this population. 1

Specific Infectious Risks to Screen For

Tuberculosis

• The prevalence of active tuberculosis in SLE patients ranges from 2.5 % to 13.8 % in endemic regions and 0 % to 1.4 % in non‑endemic regions; therefore, tuberculosis testing is recommended before initiating glucocorticoids or other immunosuppressive agents. 1

Cytomegalovirus (CMV)

• CMV antigenaemia is detected in 18 % to 44 % of SLE patients, particularly those receiving pulse methyl‑prednisolone or cyclophosphamide; CMV testing should be considered in patients on high‑dose glucocorticoid regimens. 1

Viral Hepatitis and HIV

• Screening for HIV, hepatitis B, and hepatitis C is advised prior to the commencement of immunosuppressive therapy to identify latent infections that could be reactivated. 1

Diagnostic Work‑up Recommendations

• When leukocytosis is identified, obtain appropriate cultures (blood, urine, sputum, etc.) and imaging studies guided by clinical presentation to evaluate for occult infection. 1

• In patients receiving high‑dose glucocorticoids or pulse immunosuppression, add CMV testing to the infectious work‑up. 1

Medication‑Induced Leukocytosis

• Glucocorticoid doses greater than 20 mg/day are commonly associated with drug‑induced leukocytosis (granulocytosis), which can mimic infection‑related elevations. 1

Immunologic Markers of Infection Susceptibility

• Low serum immunoglobulin levels—IgG3 ≤ 60 µg/mL or IgG4 ≤ 20 µg/mL—are linked to a heightened risk of infection in SLE patients. 1

• Peripheral lymphocyte counts ≤ 1 × 10⁹/L are associated with increased susceptibility to infectious complications. 1

Systemic Lupus Erythematosus and White Blood Cell Count

Characteristic Hematological Patterns

• The European League Against Rheumatism notes that severe neutropenia (<500 cells/mm³) and severe lymphopenia (<500 cells/mm³) are specifically monitored as infection risk factors, according to EULAR guidelines 2, 3
• Autoimmune leukopenia is common in SLE but rarely needs treatment; however, careful work-up is recommended to exclude other causes, especially drug-induced leukopenia 4, 5

Infection Diagnosis

• The European League Against Rheumatism notes that CRP levels, especially above 50 mg/L, suggest superimposed infection rather than SLE disease activity 6
• Many SLE patients rarely have elevated CRP levels during disease flares alone, making significant CRP elevation a red flag for infection 7

Treatment Considerations

• Do not overlook drug-induced leukopenia when evaluating low WBC counts, as immunosuppressive medications commonly used in SLE can cause myelosuppression 4, 5
• Leukopenia with WBC <3.0 × 10⁹/L is associated with disease activity and warrants closer monitoring, but severe neutropenia (<500 cells/mm³) requires assessment for infection risk 2