Comparison of several fixation methods for cytomegalovirus antigenemia assay

Two fixation methods based on formaldehyde or acetone for qualitative cytomegalovirus antigenemia assay were evaluated on 405 consecutive blood samples. Cytomegalovirus was detected in 40 samples by the antigenemia assay: 36 were detected by formaldehyde fixation; 22, by acetone; and 18, by both methods. Differences were statistically significant (P = 0.0043). In addition, four fixation methods (two based on formalin [with and without permeabilization] and two using acetone at different fixation times) for quantitative antigenemia assay in a different set of 32 samples from known viremic patients were evaluated. Formalin-based methods were superior to acetone-based methods, showing statistically significant differences in either the number of positive samples detected (P < 0.02; McNemar test) or the mean positive cell counts (P < 0.003; two-tailed Student's t test for paired samples). No differences between the two formalin-based methods were found. We recommend the formaldehyde fixation procedure without subsequent permeabilization because of its simplicity and sensitivity.