Table 5.
Intertest variability of the probes of GeneXpert, calculated by standard deviation of the Cq values
| GeneXpert probe and laboratory testing location | Dilution | Result with IS6110 copy no. of: |
|||
|---|---|---|---|---|---|
| 1 | 5 | 10 | 20 | ||
| A | Undiluted | 1.2 | 2.0 | 2.8 | 1.1 |
| Lab 1 | 1:1,000 | 1.0 | 0.7 | 1.0 | 1.4 |
| Lab 2 | 1:1,000 | NCa | 2.7 | 1.5 | 8.2 |
| Lab 1b | 1:10,000 | 0.9 | 0.8 | 2.8 | 1.8 |
| Lab 2 | 1:10,000 | 1.3 | 1.3 | NDc | 1.1 |
| B | Undiluted | 1.4 | 2.1 | 2.9 | 1.6 |
| Lab 1 | 1:1,000 | 1.0 | 0.7 | 1.1 | 1.3 |
| Lab 2 | 1:1,000 | NC | 2.5 | 1.3 | 7.3 |
| Lab 1 | 1:10,000 | 1.0 | 0.7 | 2.3 | 1.9 |
| Lab 2 | 1:10,000 | 1.0 | 1.8 | ND | 1.0 |
| C | Undiluted | 1.1 | 2.1 | 3.0 | 1.0 |
| Lab 1 | 1:1,000 | 1.0 | 0.7 | 1.1 | 1.4 |
| Lab 2 | 1:1,000 | NC | 2.7 | 1.4 | 8.3 |
| Lab 1 | 1:10,000 | 0.9 | 0.8 | 2.3 | 1.7 |
| Lab 2 | 1:10,000 | 1.3 | 1.6 | ND | 0.9 |
| D | Undiluted | 1.1 | 1.7 | 2.8 | 1.0 |
| Lab 1 | 1:1,000 | 1.1 | 0.6 | 1.0 | 1.3 |
| Lab 2 | 1:1,000 | NC | 2.5 | 1.4 | 8.0 |
| Lab 1 | 1:10,000 | 0.9 | 0.8 | 2.0 | 1.7 |
| Lab 2 | 1:10,000 | 1.1 | 1.5 | ND | 1.1 |
| E | Undiluted | 1.3 | 2.3 | 3.0 | 0.8 |
| Lab 1 | 1:1,000 | 1.1 | 0.7 | 1.0 | 1.3 |
| Lab 2 | 1:1,000 | NC | 2.8 | 1.6 | ND |
| Lab 1 | 1:10,000 | 0.9 | 0.9 | 2.3 | 1.8 |
| Lab 2 | 1:10,000 | 1.6 | 1.4 | ND | 1.2 |
a
NC, one of the three runs gave an error and thus the interest variability could not be calculated.
b
GeneXpert reached its analytical sensitivity with a dilution of 1:10,000 in lab 1.
c
ND, at least one run could not be detected; thus, the analytical sensitivity was not reached at this dilution.