Pediatricians and internists must consider the possibility of CGD in any person with pneumonia with a characteristic CGD organism, such as Staphylococcus aureus, Burkholderia cepacia complex, Serratia marcescens, Nocardia and Aspergillus. The most accurate test for CGD, called the dihydrorhodamine reduction (DHR), measures the ability of phagocytes to produce oxygen free radicals in phagocytes using a chemical called dihydrorhodamine. In the past, the Nitroblue Tetrazolium (NBT) slide test was used to diagnose CGD, but this is less commonly used now since it is more prone to incorrect reading. Once the diagnosis of CGD is made, it is valuable to determine the specific gene and mutation involved for purposes of prognosis and genetic counseling. The severity of CGD can partly be determined from the specific mutation in the gene and its impact on the DHR result.