Imagine that we chose 12 WBC as the cutoff score for this test, and diagnose anyone with 12 WBC or higher as having a UTI. You can see that 50% of the people with UTIs will have 12 WBC or higher, because 50% of the area under the red curve is to the right of 12 WBC. With this cutoff, the test will be 50% sensitive.
You can also see that about 2% of the people without UTIs will be diagnosed incorrectly -- false positives -- because 2% of the area under the blue curve is to the right of 12 WBC. Because 98% of the people who are healthy will test negative, the test is 98% specific.
Click in the image to choose a cutoff score for the enhanced urinalysis and learn the implications of your choice.
Using a cutoff score of 8, here's what would happen:
At this cutoff, the test is 97.8% sensitive and 50.0% specific.
It has a positive likelihood ratio (+LR) of 2 and
a negative likelihood ratio (-LR) of 0.044.