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. 2016 Sep 28;1(2):e000064. doi: 10.1136/bmjgh-2016-000064

Table 1.

Model inputs: cohort probabilities, diagnostic parameters and costs

Value Range Reference
Probability parameters
 Underlying prevalence of TB among those with a cough of at least 2 weeks' duration 5% 1–10% 24
 Prevalence of HIV among those with active TB 48% 40–60% 1
 Prevalence of HIV among those with cough but no active TB 7.2% 2–20% 1
 Probability of HIV serostatus awareness (among those with HIV/TB) 91% 80–98% 1
 Probability of HIV serostatus awareness (among those with HIV and a cough but no active TB) 63% 45–80% 1
 Probability that referral for Xpert is completed 85% 65–96% 19
 Probability of no treatment after positive Xpert result 0% 0–10% Assumption
 Probability that a patient with TB missed by screening does not return for future diagnosis and treatment 20% 11–30% 25
 Probability of empiric treatment among patients with TB testing negative 17% 8–25% 26
 Monthly probability of TB spontaneously resolving (HIV+) 0% 0–1% 27
 Monthly probability of TB spontaneously resolving (HIV−) 2% 1–6% 23
 Probability of TB cure on first-line treatment 77% 65–85% 1
 Monthly probability of death from untreated TB 1% 0.5–3% 1
 Probability of TB death on first-line treatment 6% 2–15% 1
 Probability of loss to follow-up on first-line treatment 17% * 1
Diagnostic parameters
 Sensitivity of clinical diagnosis† 44% 26–63% 26
 Sensitivity of CRP (10 mg/L as a positive screen) 98% 80–100% 28 and C Yoon et al. Under review
 Sensitivity of CXR (‘any abnormality’ as a positive screen) 98% 72–99% 29
 Sensitivity of Xpert 89% 75–95% 30
 Specificity of clinical diagnosis† 87% 81–92% 26
 Specificity of CRP (10 mg/L as a positive screen) 59% 50–68% 28 and C Yoon et al. Under review
 Specificity of CXR (‘any abnormality’ as a positive screen) 67% 50–80% 31
 Specificity of Xpert 99% 98–99% 30
Cost parameters
 CRP test US$3 US$2–US$6 Field data
 CXR US$5 US$3–US$10 32
 Xpert US$23.58 US$18–US$28 26
 First-line TB therapy (category 1—total) US$201 US$156–US$243 26
Effectiveness parameters
 Discounted life expectancy, HIV-positive 13.75 years 9–19 Assumption
 Discounted life expectancy, HIV-negative 17.87 years 13–23 Assumption

*Set equal to (1-probability of cure-probability of death).

†Probability that an individual with active TB will be referred for Xpert testing in the absence of a triage test.

CRP, C reactive protein; CXR, chest X-ray; TB, tuberculosis.