Pulmonary activity on labelled leukocyte images: patterns of uptake and their significance

The objective of this study was to characterize, and determine the significance of, pulmonary activity on labelled leukocyte images. This retrospective review included 137 immunocompetent patients who had undergone 111In labelled autologous leukocyte chest imaging and chest X-ray within 7 days. Pulmonary activity was classified as normal, focally increased, or diffusely increased. Images were correlated with chest X-rays and final diagnoses. One hundred and twelve patients (82%) had normal pulmonary activity. Seventy-six had normal chest X-rays; none had pulmonary infection. Thirty-six patients had chest X-ray abnormalities; only one had pulmonary infection. Twenty-five patients had abnormal pulmonary activity. In 13 patients it was segmental or lobar in distribution. The chest X-ray was abnormal in 12: pneumonia (11) and cystic fibrosis (one). The chest X-ray was normal in one patient with pneumonia. Two patients with non-segmental pulmonary activity did not have pulmonary infection. The chest X-ray was abnormal in one (pulmonary edema) and normal in one (sepsis). Ten patients had diffuse pulmonary activity. Chest X-ray was abnormal in two patients: adult respiratory distress syndrome (ARDS) (one) and drug toxicity (one). No patient with diffuse pulmonary activity had pulmonary infection. In summary, negative labelled leukocyte imaging excludes pulmonary infection with a high degree of certainty (the negative predictive value was 99% in this series), and can exclude pneumonia as the cause of a chest X-ray abnormality. Focal pulmonary activity strongly suggests pneumonia, while diffuse pulmonary activity is unlikely to indicate infection.