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Monday, October 20, 2008
Columbus A-C (Hyatt Regency Penns Landing)
Purpose:
Many clinicians think treatment thresholds should be adapted to the setting. We intended to explore the effect of applying a treatment threshold for pulmonary tuberculosis from a patient’s perspective, in terms of harm due to false negatives and true and false positives, at different prevalence levels in a low-income country.
Methods
In a cohort of 300 patients with chronic cough we estimated the prevalence of pulmonary tuberculosis, and the sensitivity and specificity of key predictors with latent class analysis. We computed the post-test probability of individual patients based on these data.
With disease and treatment related mortality and morbidity, and without cost or regret, we calculated the break-even point of disease probability where treating vs. not treating resulted in similar total harm from the patient’s perspective. We estimated the total harm of applying this threshold to the cohort, and to hypothetical settings with different disease prevalence.
Results
The prevalence of TB was estimated at 39%; HIV positivity and fever had a good sensitivity (both 87%); haemoptysis and apical infiltrates showed good specificity (both 87%); cavities and microscopy were highly specific (95%).
The threshold was computed at 0.026, suggesting treatment for all patients of the cohort, while clinicians only treated 125. When lowering hypothetically the prevalence in the cohort to 0.10 respectively 0.01, the lowest total harm was always found at a threshold of 0.02, coinciding with the individual patient threshold. The number of patients that would be treated when applying this threshold was 98 and 12 respectively. With a prevalence of 0.01, only 1 out of 12 patients would have negative direct microscopy.
Conclusion
For pulmonary tuberculosis a decision threshold solely based on utilities without cost or physician's regret leads to a very low threshold. The lowest total harm is found always at this disease probability, irrespective of the distribution of the patients. Although these findings might suggest an excess prescription at reference level, this is not the case in settings with lower prevalence.
Many clinicians think treatment thresholds should be adapted to the setting. We intended to explore the effect of applying a treatment threshold for pulmonary tuberculosis from a patient’s perspective, in terms of harm due to false negatives and true and false positives, at different prevalence levels in a low-income country.
Methods
In a cohort of 300 patients with chronic cough we estimated the prevalence of pulmonary tuberculosis, and the sensitivity and specificity of key predictors with latent class analysis. We computed the post-test probability of individual patients based on these data.
With disease and treatment related mortality and morbidity, and without cost or regret, we calculated the break-even point of disease probability where treating vs. not treating resulted in similar total harm from the patient’s perspective. We estimated the total harm of applying this threshold to the cohort, and to hypothetical settings with different disease prevalence.
Results
The prevalence of TB was estimated at 39%; HIV positivity and fever had a good sensitivity (both 87%); haemoptysis and apical infiltrates showed good specificity (both 87%); cavities and microscopy were highly specific (95%).
The threshold was computed at 0.026, suggesting treatment for all patients of the cohort, while clinicians only treated 125. When lowering hypothetically the prevalence in the cohort to 0.10 respectively 0.01, the lowest total harm was always found at a threshold of 0.02, coinciding with the individual patient threshold. The number of patients that would be treated when applying this threshold was 98 and 12 respectively. With a prevalence of 0.01, only 1 out of 12 patients would have negative direct microscopy.
Conclusion
For pulmonary tuberculosis a decision threshold solely based on utilities without cost or physician's regret leads to a very low threshold. The lowest total harm is found always at this disease probability, irrespective of the distribution of the patients. Although these findings might suggest an excess prescription at reference level, this is not the case in settings with lower prevalence.
See more of: Poster Session II
See more of: 30th Annual Meeting of the Society for Medical Decision Making (October 19-22, 2008)