Accuracy of blood cytological screening techniques for the diagnosis of a possible hematopoietic neoplasm in the bivalve mollusc, Mya arenaria

The two in vivo bleeding techniques currently in use in our laboratory to diagnose a hematopoietic neoplasm in Mya arenaria are: (1) phase-contrast microscopy with fresh unstained hemocytes, and (2) bright-field microscopy with Giemsa-stained hemocytes. All in vivo diagnoses were checked by histopathological studies on tissues of the same mollusc. For both methods the correct diagnosis (true + or true −) was made in 94 out of 100 clams examined. A gradation of tissue involvement was observed in the diseased clams and the accuracy of the in vivo diagnosis is related to the disease severity. There is a positive correlation between the degree of tissue involvement and the number of circulating neoplastic cells. For this reason the more extensive the neoplasm the better is the ability to diagnose the neoplasm by the in vivo bleeding techniques. Depending on the percentage of neoplastic cells present in the hemolymph, the neoplasm was graded from level 1 to 5, with 5 being the most severe. In general, at level 1, the accuracy of a single in vivo diagnosis varied from 66 to 71% and at level 2, the accuracy of diagnosis varied from 76 to 93%, while at all other levels the accuracy was 100%. The percentage of diseased clams detected by the in vivo bleeding technique was 89–91% and the percentage of nondiseased clams detected was 95%. These values can be further improved by combining the two tests and/or through multiple bleedings. Between the two types of in vivo tests, the Giemsa-stained hemocytes provided better precision of diagnosis than the fresh unstained cells, although the differences were slight.