Groups of darkly stained chromosomes may be artifacts.

Groups or conglomerations of darkly stained chromosomes (GDSC) observed in this study appeared to be artifacts as they were strictly technique dependent. Two methods of cell fixation were compared. In method I, fixative was added drop by drop to cell pellets and agitated continuously over a rotamixer. In method II, a few drops of fixative were added to hypotonic solution suspended with cells and mixed using a Pasteur pipette. In 11 patients with acute myeloid leukemia (AML) and in one patient with preleukemia studied using method I, no GDSC were found in the total of 325 metaphases examined. In 36 patients with AML, one with Klinefelter's syndrome and one with neutropenia studied using method II, GDSC were found in 18 patients. A further comparative study using different methods for cell fixation was performed in three patients. The frequency of cells with GDSC varied sharply with different methods used in two patients. In one patient the cells with GDSC were analyzed in detail. The number of darkly stained chromosomes in each cell was found to vary from 4 to 14 with a mean of 8.26 and D- and G-group chromosomes were preferentially involved.