Circulating mucin in breast carcinoma and automated leukocyte counts

Circulating mucin was found in a 40-year-old woman with metastatic ductal carcinoma of the breast. Unusually high white blood cell counts by an automated hematology cell analyzer (Ortho ELT-8/ds) did not match hemocytometer counts, prompting further investigation. The artifactually increased white blood cell count was caused by the precipitation of mucin in contact with acetic acid which was used as the red cell lysing agent prior to the automated leukocyte count. To our knowledge there is no previously published report of interference in the automated cell count by circulating mucin produced by an adenocarcinoma.