. "4 Implications for Clinical Practice and Public Health Policy." Exposure of the American People to Iodine-131 from Nevada Nuclear-Bomb Tests: Review of the National Cancer Institute Report and Public Health Implications. Washington, DC: The National Academies Press, 1999.
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Exposure of the American People to Iodine-131 from Nevada Nuclear-Bomb Tests: Review of the National Cancer Institute Report and Public Health Implications
Positive (including indeterminate results)
Diagnosis
Prior
Conditional
Product
Revised
Cancer
3%
89%
267
10.7%
No cancer
97%
23%
2,231
89.3%
Σ = 2,498
The revised probability after a positive or indeterminate result
would be only 10.7 percent, but 24.98 percent of patients would proceed to surgery (compared to 5.46 percent, as calculated above for positive FNA results) whereas 75.02 percent would avoid surgery.
In contrast, if an indeterminate result were treated as negative (i.e., the work-up stops), then the revised probability of cancer would be 0.4 percent because of false negatives. In this case, 82.78 percent of patients would avoid surgery (compared to 75.02 percent above).
Negative (including indeterminate results)
Diagnosis
Prior
Conditional
Product
Revised
Cancer
3%
11%
33
0.4%
No cancer
97%
85%
8,245
99.6%
Σ = 8,278
In a similar vein, consider the effect of an unsatisfactory FNA. Because cancers are more likely to provide satisfactory samples, an unsatisfactory result lowers the probability of cancer, as shown above, from 3 percent to 1 percent. Recall that a negative FNA only lowers the probability of cancer to 0.3 percent (because of the possibility of false-negative results).
