Use of the Nitro Blue Tetrazolium Test in Clinical Pediatrics

The rediscovery in 1966 that phagocytizing leukocytes reduce soluble yellow nitro blue tetrazolium (NBT) to an insoluble purple formazan led to the design of tests to more accurately quantitate this observation.¹ As is often the case, the initial observation of this unique response was reported in 1953² but ignored for more than a decade. Those who wish to observe NBT reduction by phagocytizing leukocytes will be both delighted and intrigued by it. The procedure is simple: a drop of anticoagulated, leukocyte-rich plasma removed from a sedimented sample of whole blood is placed on a glass slide containing a drop of NBT dissolved in normal saline and both are mixed with a suspension of ingestable particles, eg, zymosan.³ Shortly after the phagocyte reaches the particle, a violaceous color appears precisely at that point of contact. As the particle becomes entrapped within the cell, a deep purple precipitate develops