Lymphopenia in a newborn or infant is perhaps the most important indicator for urgent referral to a higher centre. Often absolute lymphocyte count is ignored in a differential count as emphasis is mainly given to total WBC and neutrophil count. Most patients with severe combined immunodeficiency are lymphopenic at birth and they are uniformly fatal before 1 year of age unless definitive therapy is instituted.
Lymphocytosis is usually a feature of viral infections and rarely points to PIDs.
Persistent Eosinophilia is observed in primary immunodeficiencies including Hyper IgE syndromes.
Monocytopenia also has been defined with primary immunodeficiencies with susceptibility to mycobacterial, fungal and viral infections.
Platelet Counts - In PIDs, thrombocytopenia has been observed as a direct effect of the disease or as a feature of autoimmunity.
Anemiais commonly observed in many immunodeficiencies as a result of repeated infections and malabsorption.