Table 1

Quality control of CD4 counts

Machine opticsFluorescent beads
AntibodyNegative controls not required for antibodies producing discrete positive and negative peaks, such as CD3, CD4, and CD8
Gating and stainingThe “lymphosum” should be checked; that is, the percentage of CD4+, CD8+, CD19+ (B cell), and CD56+ (natural killer cell) cells = 100% ±10%. US guidelines suggest doing lymphosum on each occasion. It is acceptable to do this only on new patients and in case of queries
Entire processCheck no unexpected deviations from previous counts
Daily use of commercial lyophilised cells with analysis of results. Cells from normal donors may show unexpected variations and should not be used