Circadian variations of the absolute eosinophil count and serum histaminase activity in tropical pulmonary eosinophilia.

Nine healthy volunteers and 25 tropical pulmonary eosinophilia (TPE) patients were used to study circadian variations of absolute eosinophil count (AEC) and serum histaminase activity (SHA). A marked circadian variation was found in AEC for healthy volunteers and TPE patients with the worst symptoms in the late evening and morning hours only; no rhythm could be detected in SHA for healthy subjects. However, TPE patients with worst symptoms in the late evening hours did exhibit a significant rhythm in SHA. Increased SHA in all TPE patients at all time-points of the 24 hour day-night cycle, irrespective of the worsening hours of symptoms in comparison to healthy controls, could be due to increased histamine production in such situations.