Which laboratory finding would support a diagnosis of pertussis in an adolescent?

Which laboratory finding would support a diagnosis of pertussis in an adolescent?

• A. Lymphocytosis on CBC
• B. Hyperinflation on chest x-ray
• C. Persistent night-time cough
• D. Productive cough

Answer: (A)

Pertussis often causes a distinctive lymphocytosis because the pertussis toxin disrupts lymphocyte trafficking and promotes release of lymphocytes from lymphoid tissues. A CBC showing elevated lymphocytes in the setting of compatible symptoms strongly supports the diagnosis. Imaging like hyperinflation can be seen but is not a lab finding and isn’t specific. A persistent night-time cough is a clinical symptom rather than a lab result, and a productive cough is not typical of pertussis, especially in the paroxysmal stage when the cough is usually nonproductive.

Pertussis often causes a distinctive lymphocytosis because the pertussis toxin disrupts lymphocyte trafficking and promotes release of lymphocytes from lymphoid tissues. A CBC showing elevated lymphocytes in the setting of compatible symptoms strongly supports the diagnosis.

Imaging like hyperinflation can be seen but is not a lab finding and isn’t specific. A persistent night-time cough is a clinical symptom rather than a lab result, and a productive cough is not typical of pertussis, especially in the paroxysmal stage when the cough is usually nonproductive.