Immunoradiometric assay of plasma lactoferrin.

The concentration of lactoferrin, a non-heme iron binding glycoprotein, was determined in more than 1500 EDTA plasma samples by a 2-site solid phase immunoradiometric assay to assess the significance of lactoferrin in plasma and to investigate applications for this assay. The use of commercially available antibody and antigen and a relatively short assay time make this assay more suitable for use in routine clinical laboratories than previous methods. A normal range of 250-750 micrograms/l was established. There was a correlation between plasma lactoferrin concentration and the circulating blood neutrophil count in most patients except those with splenomegaly, post-splenectomy and undergoing intensive chemotherapy. Patients with gross splenomegaly usually had an increased and post-splenectomy patients a decreased lactoferrin/neutrophil ratio indicating a respective increase and decrease in the marginated pool. In patients with acute leukemia after chemotherapy or transplantation plasma lactoferrin levels increased 1 to 5 d before blood neutrophil counts rose. As plasma lactoferrin seems to be derived from neutrophils, its concentration is probably related to the size of the total blood granulocyte pool. Calculation of the lactoferrin/neutrophil ratio demonstrated variations in the size of the bone marrow reserve and the marginated neutrophil pool.