The accuracy of Pap tests

Many women are so stressed when they receive their Pap test results that they do not even consider how accurate those results might be. While the accuracy of Pap tests has definitely improved over the years, these tests are still not 100 percent accurate.


The Pap test is also known as a Pap smear, because in the 1940s when the test was first implemented, a collection of cells was smeared onto a slide to be analyzed. A fixative, sometimes including hairspray, was used to adhere the cells to the slide. Due to this primitive method of collecting samples, false negatives were reported in approximately 20 to 45 percent Pap tests during that time. In these cases, a woman was told she had no abnormalities when there were abnormal cells in her sample.


Most modern Pap tests are now performed using a liquid-based technology. The entire cell sample is placed inside a vial of liquid and no other substances, such as fixatives, mix with the sample. This modern method of collecting samples has allowed for abnormal cells to be identified in 81 percent of Pap tests, according to a recent study by Johns Hopkins researchers. This compares with the 71 percent that was able to be identified using the old method. Today, false negatives are reported in approximately 10 to 20 percent of all negative results.


In addition to false negatives, false positives can also be reported. These, however, are much less common than false negatives. In these cases, a woman may be told that abnormal cells were found during the test when no abnormalities exist. Reports show that approximately one to ten percent of all Pap tests result in false positives.


While the newer liquid-based sample collection is much more accurate than the old method of collecting Pap smears, they still far from perfect. Using this new method, it is estimated that approximately 35 percent of cases with diseases are overlooked. Those diseases could include cervical cancer, which, if not caught early enough, can increase the chances of cancer spreading and lower a patient’s chances of survival.


Although Pap tests may not always be accurate, they are one of the most effective cancer prevention tools a woman can utilize to stay healthy. In fact, the Pap test is largely responsible for a 70 percent decrease in cervical cancer deaths in the United States in the past 50 years.


A woman who receives the results of a Pap test, whether positive or negative, may need a second opinion. Most doctors will also recommend that women over age 30 get an HPV test in conjunction with their Pap test to obtain more accurate and complete results. The Pap test will look for abnormal cells in the cervix and the HPV test will specifically look for human papillomavirus, a virus that can also cause cervical cancer.