Quality control of CD4 counts
| Machine optics | Fluorescent beads |
| Antibody | Negative controls not required for antibodies producing discrete positive and negative peaks, such as CD3, CD4, and CD8 |
| Gating and staining | The “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 process | Check 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 |