DNA analysis of atrial myxomas.

The atrial myxoma is a primary tumor of the heart which may have an uncertain clinical course. In this study, we performed flow cytometric DNA analysis of 15 paraffin-embedded atrial myxomas and correlated DNA ploidy status and proliferative fraction with clinical findings. Twelve of 15 cases (80 percent) were diploid and the remaining three cases (20 percent) were aneuploid. Two patients with aneuploid histograms were free of tumor at the time follow-up; the third patient experienced local tumor recurrence and metastases. Five patients with diploid myxomas demonstrated an elevated (greater than or equal to 17 percent) proliferative cell cycle fraction; four of these patients experienced embolic phenomenon or tumor recurrence. This pilot study suggests that an atrial myxoma with either aneuploid DNA content or elevated proliferative fraction may be associated with aggressive biologic behavior.

A radioassay for angiotensin converting enzyme.

Current methods for measuring angiotensin converting enzyme activity (EC 3.4.15.1, ACE) are somewhat cumbersome and have limited the general availability of the test. We describe here a simple four-step radioassay for ACE which uses the substrate 14C-Hippurate-L-Histidyl-L-Leucine and measures the product, 14C-Hippurate. We found that incubation at pH 7.0 (Hepes buffer) increased the sensitivity of the test by 50 percent when compared to results obtained with the pH 8.0 buffer normally used for ACE assays. A split sample comparison study between the radioassay and the spectrophotometric method showed good correlation (n = 47; mean, spectrophotometric, 26.0 U/mL; mean, radioassay, 26.1 U/mL; m = 0.86; b = 3.9; r = 0.868). We found that there was no significant difference between the spectrophotometric, kinetic and radioassay (Newman-Keuls multiple range test), but the liquid chromatographic method gave results significantly different from the other methods. The assay for ACE described here combines enhanced technical ease with the sensitivity of a radioassay.

Reference ranges for lymphocyte subsets. A comparison of standard vs rapid whole-blood lysis techniques.

Reference ranges for lymphocyte subsets may vary with processing techniques, monoclonal reagents, or analytic methods. We compared reference ranges obtained for T- and B-lymphocyte subsets by means of standard manual whole-blood lysis with a wash step vs a rapid, no-wash whole-blood lysis system. Both techniques demonstrated reference ranges similar to those in previous literature reports. The ranges established with standard and rapid lysis were similar when antibodies directed to the same cluster designation were used. Although slight statistical differences in relative percentages of CD2 and CD3 lymphocytes were observed, these differences were probably not clinically significant. These data indicate that the rapid technique provides a standardized method for enumerating T and B lymphocytes in peripheral blood.