Toward standardization of CD34+ cell enumeration: an international study

BACKGROUND: An international multicenter study, involving six sites in North America and six sites in Europe, was undertaken to assess the performance of standardized methods for the enumeration of CD34+ cells in peripheral blood over the dynamic range from 200 cells per mu L to zero. Two commercially available techniques were studied, a flow cytometry method and a microvolume fluorimetry method. STUDY DESIGN AND METHODS: Coded samples were centrally prepared and sent to test sites by overnight mail. Samples included internal replicates, linear dilutions, and specimens at the lower limit of detection. In addition, commercially available reagent positive control cells were sent to a subset of laboratories. RESULTS: Over the sample range studied, the intersite precision among different laboratories was good with coefficients of variation ranging from 14 percent to 24 percent for microvolume fluorimetry and from 20 percent to 31 percent for flow cytometry. Intrasite precision ranged from 7 percent to 21 percent. Test linearity was excellent with sites demonstrating a mean r(2) = 0.992 for microvolume fluorimetry and r(2) = 0.984 for flow cytometry. The lower limit of detection was 5 CD34+ cells per mu L for both commercial assays. Over the range of 5 to 50 CD34+ cells per mu L, the microvolume fluorimetry assay reported slightly higher values than the flow cytometry assay. Preliminary analysis of reagent positive control cells showed very good precision and accuracy. CONCLUSIONS: Standardization of CD34+ cells enumeration is improving and commercially available assays provide accurate and precise methods. More investigation of reagent positive control cells is warranted.