Circulating mucin in Wilms' tumor and nephroblastomatosis. Effect on leukocyte counts

Two children with advanced Wilms' tumor and one with extensive nephroblastomatosis showed artifactually elevated white blood cell (WBC) counts due to circulating mucin. Wilms' tumor is known to produce mucin identifiable in serum, urine, and touch imprints. To our knowledge, circulating mucin has not been described in nephroblastomatosis. When patients' blood was mixed with lysing reagent in the Ortho ELT-800, mucin was precipitated by acetic acid; this was confirmed by microscopy. Precipitates were counted as nuclei, producing abnormal WBC counts and histograms. When measured by the Ortho ELT-8/ws using osmotic lysis, the WBC counts matched hemocytometer counts. Mucin was not seen on Wright-stained smears but was evident with alcian blue staining and was largely abolished by hyaluronidase. Treatment led to disappearance of the artifactual WBC elevation.