Plasma levels of the leucocyte L1 protein in febrile conditions: relation to aetiology, number of leucocytes in blood, blood sedimentation reaction and C-reactive protein.

Plasma levels of a novel leucocyte protein (L1) were determined in a series of 176 febrile patients and compared with CRP, BLC, and BSR. Among 82 patients with bacterial infection, 81 had L1 levels above the 0.95 interval. Levels of 40 to 130 times the normal mean were seen frequently during life-threatening infections like septicaemia, meningitis, or pneumonia. In contrast, 23 of 27 patients with viral infections had normal L1 levels. A poor correlation was found between L1 levels, CRP, BLC, and BSR, suggesting that these parameters reflect different aspects of the response to tissue damage and inflammation. L1 and CRP seem equal in distinguishing between bacterial and viral infections. Low or normal L1 levels argue strongly against a bacterial infection, while elevated L1 levels discriminate poorly between bacterial and non-infectious inflammatory or malignant diseases.