Reduced neutrophil counts in patients with a viral respiratory tract infection

In patients with a viral respiratory tract infection the complete blood count (CBC) may reveal transient abnormalities. One such finding is a reduced neutrophil count, which usually does not fulfil the criteria of neutropenia but raises concerns of worsening or a more serious underlying condition. How should we interpret such results and approach such patients? What should we pay attention to?

Bertrand Godeau, MD, PhD: It is a very good question and it is difficult to answer. I think that the first point is to look at the previous blood test, because if the patient had a normal leukocyte count, it is clear that if they have a viral infection, it is probably transient neutropenia with no risk for the patient. The practice is not to perform tests and to survey your patients. Usually neutropenia will be cured spontaneously in the weeks following the viral infection.

If neutropenia is chronic, it is necessary to test for anti–white blood cell antibodies, large granular lymphocytes (LGLs), lupus, sicca syndrome, to perform tests to make sure that the patient does not have a hematological disease, and to discuss bone marrow aspiration. But if you have isolated neutropenia just after a viral infection, I think that the first step is to wait and to survey.