Markers of lymphocyte subsets used in flow cytometric evaluation of inborn errors of immunity

When ordering a flow cytometric analysis, it is important to obtain a complete blood count (CBC) with differential at the same time to allow for calculation of the absolute numbers of each subset of lymphocytes. Each has clinical significance in different contexts. For T cell lymphopenias in the newborn period, the proportion of naïve T cells is paramount to determining whether the genesis of T cells is compromised. Similarly, the proportion of memory B cells among the total B cells is key to ascertain if there is a block on the progression of B cell development, as often seen in the common variable immunodeficiency (CVID) phenotype. On the other hand, in adulthood, the absolute number of naïve helper T cells is often prognostic for the susceptibility to opportunistic infections.