Table 2.
Limit of detection, accuracy and standard deviation of four cobas HBV assays* (N = 1170).
| Nominal titer (IU/ml) |
cobas 6800/8800 | cobas 4800 HBV | CAP/CTM HBV v2 | HPS/CTM HBV v2 | |
|---|---|---|---|---|---|
| (IU/ml) | (log10 IU/ml) | % (#) | % (#) | % (#) | % (#) |
| 2.000 | 3.3 | 100 (42/42) | 100 (40/40) | 100 (40/40) | 100 (40/40) |
| 200 | 2.3 | 100 (48/48) | 100 (40/40) | 100 (40/40) | 100 (40/40) |
| 60 | 1.78 | 100 (48/48) | 100 (40/40) | 100 (40/40) | 100 (40/40) |
| 20 | 1.3 | 100 (48/48) | 100 (40/40) | 100 (40/40) | 100 (40/40) |
| 10 | 1 | 100 (48/48) | 100 (40/40) | 95.0 (38/40) | 97.5 (39/40) |
| 5 | 0.7 | 100 (48/48) | 100 (40/40) | 77.5 (31/40) | 95.0 (38/40) |
| 2,5 | 0.4 | 83.3 (40/48) | 75.0 (30/40) | 47.5 (19/40) | 60.0 (24/40) |
|
LoD$via PROBIT
95% hit rate (IU/ml) (95%CI) |
2.7 (nc–nc) |
2.8 (nc–nc) |
9.6 (7.3–16.5) |
6.2 (4.8–10.8) |
|
|
LoD ⩾ 95% hit rate
(IU/ml) |
5 | 5 | 10 | 5 | |
|
Average accuracy‡
(log10 IU/ml) |
0.05 | 0.04 | 0.04 | –0.16 | |
|
Standard deviation (log10 IU/ml)
(min, max) |
(0.04, 0.14) | (0.06, 0.24) | (0.05, 0.16) | (0.07, 0.15) | |
*
cobas 6800/8800 HBV, cobas HBV test for use on the cobas 6800/8800 Systems; cobas 4800 HBV, cobas HBV test for use on the cobas 4800 Systems; CAP/CTM HBV v2, COBAS AmpliPrep/COBAS TaqMan HBV v2 test; and HPS/CTM HBV v2, COBAS TaqMan HBV test for use with the High Pure System.
$
LoD was calculated using panel members with concentration ranging from 2.5 to 2000 IU/ml.
‡
Average accuracy and standard deviation were calculated using panel members with nominal concentration within each assay linear range.
CI, confidence interval; HBV, hepatitis B virus; LoD, limit of detection; nc, noncalculable.