Effect of leukocyte concentration and inoculum volume on the laboratory identification of cytomegalovirus in peripheral blood by the centrifugation culture-antigen detection methodology.

OBJECTIVE

To investigate the rate of Cytomegalovirus (CMV) detection in peripheral blood by shell vial assay-indirect immunofluorescent assay technology using two leukocyte inocula concentrations and different inoculum volumes containing equivalent cell concentrations.

DESIGN

Leukocyte inocula concentrations of 2 x 10(5) and 4 x 10(5) cells per 0.2 mL were assayed for the presence of CMV by shell vial assay-indirect immunofluorescent assay. The effect of different inoculum volumes (0.2 and 0.4 mL) containing an equivalent cell concentration of 4 x 10(5) was evaluated as well. The data were compared to conventional MRC-5 tube cultures, including blind passage.

PATIENTS

Ninety-five patients (101 specimens) were tested sequentially. The test population consisted primarily of patients suffering from the acquired immunodeficiency syndrome.

SETTING

The diagnostic virology laboratory, acquired immunodeficiency syndrome clinics, and hospital wards.

RESULTS

Among the 101 specimens tested by shell vial assay-indirect immunofluorescent assay, the rate of CMV sensitivity increased by 36% using the higher leukocyte inoculum concentration of 4 x 10(5) cells per 0.2 mL (P = .002; Cochran's Q test). No significant difference in CMV yield was identified using equivalent cell concentrations with inocula volumes of 0.2 or 0.4 mL. The CMV sensitivity rate using the higher leukocyte inoculum surpassed that obtained by conventional tube culture-blind passage.

CONCLUSION

These data denote the importance of leukocyte concentration on the rate of CMV detection in peripheral blood by the shell vial assay-indirect immunofluorescent assay. The data also point out the need to establish a standardized blood preparation protocol to achieve optimal clinical relevance of this widely used laboratory test.