Full blood count and differential. If neutropenia, identify cause. If neutrophil count normal, depending on clinical features tests for chronic granulomatous disease (nitro blue tetrazolium assay, dihydro rhodamine assay) or leukocyte adhesion defect type 1 (CD18, CD 11 a, CD 11b, CD 11c by flowcytometry) and type 2 (CD 15 by flowcytometry). Here, ITGB2 is linked to neutropenia.