TABLE 2.
Performance of HIV-1 viral load assays according to HIV subtype
| Parameter | No. (%) of patients with indicated result based on: |
|||
|---|---|---|---|---|
| m2000rt | TaqMan 48 | NucliSens Easy Q v1.2 | Versant 3.0 | |
| No. of overall results obtained (n = 369 patients) | 371 (100) | 357 (97) | 338 (92) | 276 (75) |
| TND or no amplificationa | 74 (20) | 69 (19) | 23 (7) | NA |
| Subtype B | 12 (16) | 10 (14) | 13 (57) | |
| Non-subtype B | 62 (84) | 59 (86) | 10 (43) | |
| <LDL log10 copies/ml | 28 (7.5) | 24 (7) | 74 (22) | 109 (39) |
| Subtype B | 7 (25) | 7 (29) | 16 (22) | 20 (18) |
| Non-subtype B | 21 (75) | 17 (71) | 58 (88) | 89 (82) |
| False-negative resultb (n = 38 samples) | 8 (2) | 9 (2.5) | 20 (6) | 5 (2) |
| Subtype B | 4 (50) | 6 (67) | 7 (35) | 0 |
| Non-subtype B | 4 (50) | 3 (33) | 13 (65) | 5 (100) |
| Underquantified result ≥1.0 log10 copies/mlc (n = 50 samples) | 5 (1.3) | 7 (2) | 15 (4.4) | 26 (9.4) |
| Subtype B | 2 (25) | 3 (43) | 4 (27) | 5 (19) |
| Non-subtype B | 3 (75) | 4 (57) | 11 (73) | 21 (81) |
| Underquantified result ≥0.5 and <1.0 log10 copies/mlc (n = 95 samples) | 23 (9) | 20 (6) | 61 (18) | 68 (25) |
| Subtype B | 11 (48) | 13 (65) | 26 (43) | 26 (38) |
| Non-subtype B | 12 (52) | 7 (35) | 35 (57) | 42 (62) |
| Falsely high (VL ≥1.0 log10 copies/ml [n = 4]) | None | 1 CRF02_AG | 1 C | 2 (1) (1 B and 1 AE) |
| Total discordant resultsd | 13 (3.5) | 17 (5) | 36 (11) | 33 (12) |
All of the real-time assay results are reported as target not detected (TND) or no amplification (EQ) result if no HIV-1 RNA was detected. NA, not applicable.
Defined as a TND result for a real-time assay where all of the other assays detected HIV-1 RNA above the LDL or where an assay gave a result <LDL while all of the other assays gave an HIV-1 VL of > 2.0 log10 copies/ml higher. Three samples were false negative by more than one assay.
A total of 144 samples were underquantified by one or more assays as follows (number of samples underquantified in parentheses): m2000rt (8), CAP-CTM (8), EQ (40), bDNA (36), m2000rt + EQ (2), m2000rt + CAP-CTM (2), m2000rt + bDNA (10), CAP-CTM + EQ (7), CAP-CTM + bDNA (2), EQ + bDNA (22), CAP-CTM + EQ + bDNA (3), and m2000rt + EQ + bDNA (4).
Results include false negatives, falsely high results, and results underquantified by ≥1.0 log10 copies/ml. The total number of results for each assay was used to calculate the percentages.