Current laboratory practices in flow cytometry for the enumeration of CD 4(+) T-lymphocyte subsets

CD4(+) T-lymphocyte subset enumeration is routinely used for monitoring HIV disease progression, with approximately 300,000 tests performed annually in the UK alone. Technical variables can impact upon any laboratory test and therefore the final result obtained. Here, we report the findings of a survey questionnaire issued to 1,587 clinical flow cytometry laboratories to: (a) determine if the UK NEQAS for Leucocyte Immunophenotyping (UK NEQAS LI) lymphocyte subset external quality assessment (EQA) programme was suitable for current laboratory needs and practices; and (b) assess the impact of these responses on clinical practice where CD4(+) T-lymphocyte subsets analysis is undertaken. The survey covered areas not traditionally examined by EQA such as: staffing numbers, flow cytometer age and service intervals, plus six test specific sections covering: leukaemia immunophenotyping, CD4(+) T-lymphocyte subsets analysis (reported here), CD34(+) stem cell testing, low level leucocyte enumeration, minimal residual disease testing and PNH testing.

The responses revealed major methodological variations between centres undertaking CD4(+) T-lymphocyte subset analysis. Significant differences existed in basic laboratory practices such as: normal range derivation; pipetting techniques; instrument maintenance and units of reporting, all of which results in non-adherence to international guidelines.

Despite the availability of international guidelines our survey highlighted a lack of concordance amongst laboratory techniques. Such variation could adversely impact on patient care and clinical trial data. Therefore, it is recommended centres undertaking flow cytometric CD4(+) T-lymphocyte subsets analysis urgently review their methodologies and normal ranges to ensure they are fit for purpose and meet current international guidelines.