Table 3

Incidence rates (IRs//1000 person-years) and predictive values for incident TB from the time of QuantiFERON TB-Gold (QFT) testing, by observation time (</>2 years) and interferon-γ (IFN-γ) category*

QFT resultnYearsTBIRPPV (hPPV)†NPV (hNPV)†
<2 years after QFT(or until TB, LTBI treatment, death, emigration or study end)
Total study population44 87580 2702052.6(0.5)(99.5)
 Positive, total9 87815 80217611.11.8
   Low positive21663593143.90.6
   Medium positive26704259388.91.4
   High positive5042795012415.62.5
Negative34 12863 064240.499.9
Positive, by age (years)
Any medical risk factor17 10130 734270.9
 Positive, total13762074188.71.3
  Low positive47874622.30.4
  Medium positive41861123.30.5
  High positive4807071419.82.9
Negative15 17627 80870.399.9
Foreign-born, total19 41834 0101835.4(0.9)(99.1)
 Positive, total830613 48016412.22.0
  Low positive14742497135.20.9
  Medium positive217635533610.11.7
  High positive4656743011515.52.5
Negative10 87120 147140.799.9
Norwegian-born, total25 45746 26222.5(0.09)(99.9)
 Positive, total15722322125.20.8
  Low positive692109610.90.1
  Medium positive49470622.80.4
  High positive386520917.32.3
Negative23 25742 917100.299.9
≥2 years after QFT (until TB, LTBI treatment, death, emigration or study end)
Total study population39 94288 520520.6(0.1)(99.9)
 Positive, total713217 041432,50.6
  Low positive1679409530.70.2
  Medium positive1910470381.70.4
  High positive35438243323.90.9
Negative32 12470 12390.199.9
  • *Low positive, IFN-γ 0.35 to <1.0; medium positive, IFN-γ 1.0 to <4.0; and high positive, IFN-γ>4.0 IU/mL.

  • †For a hypothetical test in which all individuals tested positive (for hPPV) or all tested negative (for hNPV).

  • hNPV, hypothetical negative predictive value; hPPV, hypothetical positive predictive value; LTBI, latent TB infection; Years, sum of person-years follow-up.