Interpretation of lymphocyte subset counts by the general pediatrician

The immune system poses one of the greatest challenges for the scientific community. The general pediatrician should be able to screen and identify an immunodeficient patient based on certain clinical indications. Further investigation is crucial for the distinction between primary or secondary immunodeficiency as well as for between cellular and humoral immunity defects. Full blood count is the best initial laboratory test when suspecting a primary immunodeficiency, focusing on the absolute lymphocyte count, while lymphocyte subset count offers the advantage of detecting the cell type that causes the immune defect. The aim of the present review was to guide the general pediatrician in the investigation and diagnosis of an immunodeficient patient. Even though an immunodeficiency may seem a very difficult disease to diagnose, a balanced and rational way of thinking, along with the help of modern technological advances, can easily guide us in the right direction.