To determine the potential advantage of single-platform technology in the enumeration of CD4+ T lymphocyte and CD34+ stem cells, data has been analysed from the UK NEQAS for Leucocyte Immunophenotyping schemes. The inter-laboratory CVs for CD4+ T lymphocyte counts were consistently lower for single-platform (mean 13.7%, range 10-18.3%) compared to dual-platform methodology (mean 23.4%, range 14.5-43.7%). Subgroup analysis of single-platform users demonstrated mean overall inter-laboratory CVs of 17.2%, 13% and 7.1% for the FlowCount, TruCount and volumetric approach respectively. The lowest inter-laboratory CVs obtained for a single sample by each single platform approach were 4% (TruCount), 4.4% (volumetric), 4.6% (FACSCount) and 12.7% (FlowCount). Similarly, the mean inter-laboratory CV for CD34+ stem cell enumeration using non-standardized single-platform approaches was 18.6% (range 3.1-36.9%) compared to 28.6% (range 19-44.2%) for the dual-platform technology. Our results suggest absolute cell subset enumeration should be performed by single-platform technology and that such an approach should improve the quality control of multi-centre clinical trial data for CD4+ T lymphocyte and CD34+ stem cells.

Summary Analysis of short tandem repeats (STR) is the predominant method for post‐transplant monitoring of donor engraftment. It can enable early detection of disease relapse, level of engraftment and provide useful information on the graft‐versus‐host disease (GVHD)/graft‐versus‐tumour (GVT) effect, facilitating therapeutic intervention. Harmonization and standardization of techniques and result interpretation is essential to reduce the impact of laboratory variability on both clinical management and the results of multi‐centre clinical trials. However, the United Kingdom National External Quality Assessment Service for Leucocyte Immunophenotyping (UK NEQAS LI) has highlighted significant issues inherent in STR testing that impact upon inter‐ and intra‐ laboratory variation. We present here consensus best practice guidelines and recommendations for STR chimerism testing, data interpretation and reporting that have been drawn up and agreed by a consortium of 11 UK and Eire clinical laboratories. This document uses data obtained from the UK NEQAS LI Post‐Stem Cell Transplant (SCT) Chimerism Monitoring Programme.

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The human immunodeficiency virus (HIV) global epidemic has necessitated the routine enumeration of T-lymphocyte subsets, which has created a need for external quality assurance (EQA). The United Kingdom National External Quality Assessment Scheme (UK NEQAS) for Immune Monitoring provides EQA for 296 laboratories in 40 countries. In 1993, UK NEQAS developed and incorporated into its program stabilized whole blood that enables the accurate monitoring of laboratory performance. Overall, the mean interlaboratory coefficient of variation (CV) for percentage CD4 ؉ T-lymphocyte subset enumeration has fallen from 15% to less than 5%, as a direct result of the increased use of CD45/ side scatter (SSC) gating. Laboratories using alternative gating strategies (i.e., CD45/CD14 or forward scatter [FSC]/SSC) were about 7.4 times more likely to fail an EQA exercise. Furthermore, the adoption of single-platform technology resulted in a reduction of the overall mean interlaboratory CV for absolute CD4 ؉ T lymphocytes from 56% (prior to the widespread use of single-platform technology) to 9.7%. Individual laboratory deficiencies were also identified using a performance monitoring system and, through re-education by collaboration with the coordinating center, satisfactorily resolved. In conclusion, during the last 9 years, the UK NEQAS for Immune Monitoring program has highlighted the significant technological advances made by laboratories worldwide that undertake lymphocyte subset enumeration. Cytometry (Clin. Cytometry) 50:102-110, 2002.

Summary. The European Working Group on Clinical CellAnalysis (EWGCCA) has, in preparation for a multicentre peripheral blood stem cell clinical trial, developed a singleplatform¯ow cytometric protocol for the enumeration of CD34 stem cells. Using this protocol, stabilized blood and targeted training, the EWGCCA have attempted to standardize CD34 stem cell enumeration across 24 clinical sites. Results were directly compared with participants in the UK National External Quality Assessment Scheme (NEQAS) for CD34Stem Cell Quanti®cation that analysed the same specimens using non-standardized methods. Two beadcounting systems, Flow-Count and TruCount, were also evaluated by the EWGCCA participants during trials 2 and 3. Using Flow-Count, the intralaboratory coef®cient of variation (CV) was # 5% in 39% of the laboratories (trial 1), increasing to 65% by trial 3. Interlaboratory variation was reduced from 23´3% (trial 1) to 10´8% in trial 3. In trial 2, 70% of laboratories achieved an intralaboratory CV # 5% using TruCount, increasing to 74% for trial 3; the interlaboratory CV was reduced from 23´4% to 9´5%. Comparative analysis of the EWGCCA and the UK NEQAS cohorts revealed that EWGCCA laboratories, using the standardized approach, had lower interlaboratory variation. Thus, the use of a common standardized protocol and targeted training signi®cantly reduced intra-and interlaboratory CD34 cell count variation.