Table 2. Operating characteristics of dedicated single platform CD4+ T-cell enumeration systems.
| DEDICATED SINGLE PLATFORM CD4 SYSTEMS | ||||
|---|---|---|---|---|
| Assay name | FACSCount | Guava PCA | Partec CyFlow Counter or CyFLow SL_3 | Apogee Auto40 |
| Manufacturer | Becton Dickinson | Millipore (formerly Guava Technologies and now a division of Merck) | Partec | Apogee flow systems |
| Instrumentation | Flow cytometer | Flow cytometer | Flow cytometer | Flow cytometer |
| Assay principle | Dedicated single platform bead-based flow cytometer, two colour, no-lyse no-wash | Single platform volumetric flow cytometer. Microcapillary flow cell. Previously used EasyCD4 reagents (EasyCD4 system), since replaced by Auto CD4/CD4%. Company also produces the more complex easyCyte instruments, for research use only. | Volumetric SP flow cytometer. Up to 3 parameters (2 colour plus SSC). Simplest is single parameter CD4. For CD4%, 2 colour (CD45/4) + SSC. SL_3 (also called SL green) operates on the same principles but is adaptable to wider applications. Other CyFlow instruments such as SL blue have a wider range of parameters and potential applications. | Volumetric flow cytometer |
| Parameters measured | Absolute CD4 count and CD4% | Absolute CD4 count and CD4% | Absolute CD4 count and CD4% | Absolute CD4 and CD4% |
| Specimen | 50μl whole blood in EDTA | 10μl whole blood in EDTA | 20μl whole blood in EDTA | 50μl whole blood in EDTA |
| Throughput | ≥30 samples/hour, at CD4 counts≥400 | 100–150 samples/day | 250 samples/day, 400 samples/day with loader | 20 samples/hour |
| Compatible with independent EQA/PT programmes? | Yes | Yes | Yes | No data available |
| Is there access to compatible full process QC reagent? | Yes | No manufacturer-produced full process control | Manufacturer produces dry stabilised control blood | No manufacturer-produced full process control |
| Maximum length of time from blood draw to testing | Stain within 48 hours of draw (24 hours for CD4%) (store at 20–25°C), analyse within 48 hours of staining. | 48 hours | 48 hours | Preferably run within 6–8 hours unless stabilised |
| Can the test be performed on fixed/ stabilised blood | Yes | Yes | Yes | Yes |
| Complexity/training required | One day training | One day training | Moderate training requirement | One day training |
| Environmental/energy issues | Requires uninterrupted mains electricity | Requires uninterrupted mains electricity Less biohazardous waste (reduced by 100 fold) | Mains electricity or car battery or solar panels | UPS with battery back up included. Optional inverter allows instrument to be powered by vehicle battery |
| Robustness to heat/humidity | 10–35°C, 5–95% non-condensing humidity. Reagents require refrigeration. | Instrument: up to 35°C. 10–90% non-condensing relative humidity. Reagents require refrigeration. | Solid state laser more stable than water or air cooled gas lasers at high temperatures. Liquid reagents require refrigeration, or dry reagent kits available which can be stored at up to 60°C in dark for up to 12 months | Option of thermostable reagents with 9 month shelf life at room temperature. Instrument: 5–35°C, <90% humidity. |
PCA = personal cell analysis, SSC = side scatter.