False-positive results for HIV and STS for MT and DBS
| Blood collection system | STI tested | Reactive tests, n (%) | Confirmed reactive tests, n (%) | False positive, n (%) |
| MT | HIV | 35/561 (6.2) | 1/30* (3.3) | 29/556* (5.2) |
| DBS | HIV | 13/2583 (0.5) | 1/11* (9.1) | 10/2582* (0.4) |
| p value Percentage difference (95% CI) | – | <0.001 −5.7 (−7.8 to −3.7) | 0.470 5.8 (n/a) | <0.001 −4.8 (−6.7 to −3.0) |
| MT | STS | 6/544 (1.1) | 4/6 (66.7) | 2/544 (0.4) |
| DBS | STS | 17/2579 (0.7) | 16/16* (100.0) | 0/2578* (0.0) |
| p value Percentage difference (95% CI) | -- | 0.271 −0.4 (−1.4 to 0.5) | 0.065 33.3(n/a) | 0.030 −0.4 (n/a) |
p values in bold typeface denote statistical significance; p values rounded to three decimal places.
For proportion percentage differences with 95%CI, negative values favour MT, and positive values favour DBS.
*Numerical reductions due to no evidence of confirmatory test by service provider or general practitioner.
DBS, dried blood spot; MT, mini tube; n/a, not applicable; STS, serological test for syphilis.