Table 1. Operating characteristics of flow cytometric methods for CD4+ T-cell enumeration, using conventional flow cytometers.
| FLOW CYTOMETRY USING CONVENTIONAL FLOW CYTOMETER a | |||||
|---|---|---|---|---|---|
| Conventional dual platform | Bead-based single platform technology on conventional flow cytometer | Panleucogating | |||
| Assay name | Various | Trucount tubes | Flow-Count beads | Perfect-Count | PLG CD4 |
| Manufacturer | Various | Becton Dickinson | Beckman Coulter | Cytognos | Beckman Coulter |
| Compatible with various reagent systems and flow cytometers | Compatible with various reagent systems and flow cytometers | ||||
| Instrumentation | Flow cytometer plus haematology analyser | Flow cytometer | Gating strategy | ||
| Assay principle | Absolute count calculated using results from flow cytometry together with the total lymphocyte count from haematology analyser | Absolute CD4 counts determined using ratio of CD4 to a known quantity of fluorescent beads—no need for haematology analyser | Gating strategy using total white cell count | ||
| Trucount tubes contain premeasured quantity of lyophilised beads | Liquid beads need accurate pipetting by operator | Two different bead populations allow detection of inadequate mixing | |||
| Parameters measured | Absolute CD4 and CD4% | Absolute CD4 and CD4% | Absolute CD4 and CD4% | ||
| Others depend on reagent kits/methods | |||||
| Specimen | 500μl whole blood in EDTA | Up to 100μl whole blood in EDTA | 100μl whole blood in EDTA | ||
| Throughput | Up to 250 samples/day | Up to 250 samples/day | Up to 250 samples/day | ||
| Compatible with independent EQA/PT programmes? | Yes | Yes | Yes | Yes | Yes |
| Is there access to compatible full process QC reagent? | Yes | Yes | Yes | Yes | N/A |
| Maximum length of time from blood draw to testing | 24 hours | 24 hours | 5 days | ||
| Can the test be performed on fixed/ stabilised blood | Yes | Yes | Yes | Yes | Yes |
| Complexity/training required | Complex. Significant training required. | Complex. Significant training required | Moderate training requirement | ||
| Environmental/energy issues | Requires uninterrupted mains electricity | Requires uninterrupted mains electricity | Requires uninterrupted mains electricity | ||
| Robustness to heat/humidity | Climate control recommended | Climate control recommended | Climate control recommended | ||
| Reagents require refrigeration | Reagents require refrigeration | Reagents require refrigeration | |||
a Various flow cytometers available from various manufacturers. Examples include Becton Dickinson FACSCalibur, Beckman Coulter Epics XL.