The Pap test has a notoriously low sensitivity. Let\'s now administer a second s

Question

The Pap test has a notoriously low sensitivity. Let's now administer a second screen to those with positive Pap tests. The patient must be identified as positive by this second screen as well in order to be diagnosed. The second screen is an HPV DNA test for high-risk strains of the virus. The sensitivity of the DNA test is 94.6% and the specificity is 94.1%.

Construct a 2x2 table for those 1134 who tested positive with the Pap test, and who will now undergo HPV DNA testing. Calculate both the net sensitivity and net specificity of these screens.

What does this tell you?

Given the results of the calculations, what would your recommendation be in order to best screen for cervical cancer risk among patients?

Explanation / Answer

Number of Patients who tested positive with the Pap test=1134

Now apply HPV DNA test and the sensitivity (i.e. the percentage of sick people who are correctly identified as having the condition) of the DNA test is 94.6% and the specificity (i.e. the percentage of healthy people who are correctly identified as not having the condition) is 94.1% and these are represented as follows:

Following is a 2x2 table for 1134 who tested positive with Pap test and who will now undergo HPV DNA testing:

Total no. of both the net sensitivity of these screens (i.e. Pap test+DNA test)=1134+1073=2207

Total no. of both the net specificity of these screens (i.e. Pap test+DNA test)=1067

Ratio of net specificity and net sensitivity=1067/2207=0.48 which is alomost equal to 0.5. Hence chance of cervical cancer of each patient is almost 0.5 i.e. risk is almost 0.5.

Hence it is not justified to go through these two test procedures becuase it increases fear among patients and it is also time consuming method. Hence the recommendation is to test only HPV DNA test for detecting cervical cancer.

People having cervical cancer People having not cervical cancer Test positive 0.946 0.059
Test Negative 0.054
0.941

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