Neutrophil alkaline phosphatase activity in respiratory viral infection

Neutrophil alkaline phosphatase (NAP) is used as a diagnostic marker in several hematological disorders. In regard to the role of NAP in infectious diseases, previous investigators have presented the hypothesis that NAP activity is useful to distinguish viral infections from bacterial infections. Because the numbers of patients enrolled in previous studies of viral infections were limited, we intended to evaluate the hypothesis by measuring NAP activity in a large number of pediatric patients with respiratory viral infections. A cytochemical analysis of NAP was performed in 160 patients with various types of respiratory infections. In patients with adenovirus or respiratory syncytial (RS) virus infection, NAP activity was significantly higher than the control value newly established at our department, while in patients with Epstein-Barr virus, measles, or influenza infection, it was comparable to the control value. On an individual basis, NAP scores (determined from NAP cytochemical activity) in 22 of 26 patients (84.6%) with adenovirus infection, and 31 of 42 patients (73.8%) with RS virus infection were found to exceed the 95% confidence upper limit of the control group. In conclusion, NAP activity is quite varied among different respiratory viral infections. When NAP activity is high in respiratory infections, adenovirus or RS virus infection, as well as bacterial infections, should be taken into consideration.