PPT Slide
Assume that the cutoff point for this test that designates toxicity is 2.0 ng/mL in your laboratory.
Moreover, you understand that in using any cutoff point, you inevitably create false-positive and false-negative results.
If the test result is normal (e.g., 1.5 mg/mL), how far down has the probability estimate of 50% fallen?
If the test result is abnormal (2.5 ng/mL), how much more certain are you that the patient has digitalis intoxication?
The decision on further management hinges on this issue.