Spontaneous test with NST
Last reviewed: 23.04.2024
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Spontaneous test with NST (nitrosinium tetrazolium) allows to evaluate the state of oxygen-dependent bactericidal mechanism of phagocytes (granulocytes) of blood in vitro.
Normally, the number of HCT-positive neutrophils in adults is up to 10%.
It characterizes the state and degree of activation of the intracellular NADP-H-oxidase antibacterial system. The principle of the method is based on the restoration of the absorbed phagocyte soluble HCT dye into insoluble diformazan under the influence of superoxidanion (intended for intracellular destruction of the infectious agent after its absorption), formed in the NADPH-oxidase reaction. Indicators of the NST test are increased in the initial period of acute bacterial infections, whereas in the subacute and chronic course of the infectious process, they decrease. Sanitation of the organism from the pathogen is accompanied by the normalization of the indicator. A sharp decline indicates a decompensation of anti-infectious protection and is considered a prognostically unfavorable sign.
The test with the NST plays an important role in the diagnosis of chronic granulomatous diseases, which are characterized by the presence of defects in the NADP-H-oxidase complex. Patients with chronic granulomatous diseases are characterized by the presence of recurrent infections (pneumonia, lymphadenitis, lung, liver, skin abscesses) caused by Staphylococcus aureus, Klebsiella spp., Candida albicans, Salmonella spp., Escherichia coli, Aspergillus spp., Pseudomonas cepacia, Mycobacterium spp. And Pneumocystis carinii.
Neutrophils in patients with chronic granulomatous diseases have normal phagocytic function, but due to a defect in the NADP-H-oxidase complex they are not capable of destroying microorganisms. Hereditary defects of NADP-H-oxidase complex are in most cases linked to chromosome X, less often autosomal recessive.
Reduction of the spontaneous test with NST is characteristic for chronic inflammation, congenital defects of the phagocytic system, secondary and primary immunodeficiencies, HIV infection, malignant neoplasms, severe burns, trauma, stress, malnutrition, treatment with cytostatics and immunosuppressants, and exposure to ionizing radiation.
An increase in the spontaneous test with NST is noted in antigenic stimulation due to bacterial inflammation (prodromal period, acute manifestation of infection with normal phagocytosis activity), chronic granulomatosis, leukocytosis, enhancement of antibody-dependent cytotoxicity of phagocytes, auto-allergic diseases, allergies.
Activated test with NST
Normally, the number of HCT-positive neutrophils in adults is 40-80%.
The activated test with NST allows to evaluate the functional reserve of the oxygen-dependent bactericidal mechanism of phagocytes. The test is used to identify the reserve capacity of intracellular phagocyte systems. With preserved intracellular antibacterial activity in phagocytes, there is a sharp increase in the amount of formazan-positive neutrophils after their stimulation with latex. Reduction of the parameters of the activated HCT-test of neutrophils below 40% and monocytes below 87% indicates a lack of phagocytosis.
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