Table 3

False-positive results for HIV and STS for MT and DBS

Blood collection systemSTI testedReactive tests, n (%)Confirmed reactive tests, n (%)False positive, n (%)
MTHIV35/561 (6.2)1/30* (3.3)29/556* (5.2)
DBSHIV13/2583 (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)
MTSTS6/544 (1.1)4/6 (66.7)2/544 (0.4)
DBSSTS17/2579 (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.