BACKGROUND: The United Kingdom National External Quality Assessment Service (UK 
NEQAS) for Leucocyte Immunophenotyping Immune Monitoring Programme, provides 
external quality assessment (EQA) to non-U.S. laboratories affiliated with the 
NIH NIAID Division of AIDS (DAIDS) clinical trials networks. Selected 
laboratories are required to have oversight, performance monitoring, and 
remediation undertaken by Immunology Quality Assessment (IQA) staff under the 
DAIDS contract. We examined whether laboratory accuracy improves with longer EQA 
participation and whether IQA remediation is effective.
METHODS: Laboratory accuracy, defined by the measurement residuals from trial 
sample medians, was measured on four outcomes: both CD4+ absolute counts 
(cells/μL) and percentages; and CD8+ absolute counts (cells/μL) and percentages. 
Three laboratory categories were defined: IQA monitored (n = 116), United 
Kingdom/non-DAIDS (n = 137), and non-DAIDS/non-UK (n = 1034). For absolute count 
outcomes, the groups were subdivided into single platform and dual platform 
users.
RESULTS: Increasing EQA duration was found to be associated with increasing 
accuracy for all groups in all four lymphocyte subsets (P < 0.0001). In the 
percentage outcomes, the typical IQA group laboratory improved faster than 
laboratories from the other two groups (P < 0.005). No difference in the overall 
rate of improvement was found between groups for absolute count outcomes. 
However, in the DPT subgroup the IQA group ultimately showed greater 
homogeneity.
CONCLUSIONS: EQA participation coupled with effective laboratory monitoring and 
remedial action is strongly associated with improved laboratory accuracy, both 
incrementally and in the proportion of laboratories meeting suggested standards. 
Improvement in accuracy provides more reliable laboratory information 
facilitating more appropriate patient treatment decisions. © 2017 International 
Clinical Cytometry Society.