Every three to five years, women aged 21 to 65 visit their gynecologist and have a Pap test done as part of their examination. You know, the one where the doctor does something with a device that looks kind of like a long Q­ tip and then bags up it up and for most, that’s it. Unless you’re one of the many who gets a call later saying your Pap came back with some kind of abnormal result.

Considering how many women undergo a Pap test each year, it’s surprising how few have any idea what the test is for. A Pap (short for Papanicolaou) test is actually a screening test for cervical cancer. It doesn’t test for ovarian cancer, it doesn’t test for uterine cancer, it isn’t some kind of test for fertility or for sexually transmitted diseases. No, it just tests for the possible presence of cervical cancer or pre­-cervical cancer.

A Pap is a rather simple test­. The doctor sticks a brush­like device up your vagina and takes a small sample of cells from your cervix. The sample is shipped off to a laboratory where the cells are stained and examined under a microscope. The cells are being examined for signs of abnormalities that may indicate cervical cancer is beginning to develop, or is already present.

Screening vs. diagnostic test

A Pap test is a screening test, not a diagnostic test. What is the difference? Well, a diagnostic test is intended to assist in diagnosing a disease ­- to help answer the question “is the disease present or not?” Diagnostic tests are generally only used if the patient is exhibiting signs or symptoms suggestive of a disease being present. Screening tests are applied to patients who do not exhibit any signs or symptoms, and they are intended to rule out the possibility of disease.

So you show up at the doctor’s office with no signs or symptoms, and the doctor performs a Pap test to rule out the possibility of cervical cancer. An ideal screening test will have a very high sensitivity for the condition­ - it will not miss any cases of cervical cancer present. In an ideal world, a screening test will also have a very high specificity, but in actual real life, in order to not miss any cases of cervical cancer, a screening test will tend to have a measurable rate of false­ positives (a lower specificity).

That sounds like mumbo-­jumbo, of course, so let’s try to put it into a more readily understandable example. Let’s say you’re trying to keep peanuts out of your school cafeteria because three young children in the school are dangerously allergic to peanuts. So you devise rules to absolutely ensure that no peanuts sneak in. One rule you come up with is “No home­baked goodies.” This rule will ensure that no child accidentally brings in a home­made cookie with peanuts in it (a high sensitivity for peanuts), but it also means a lot of food that doesn’t have peanuts in it is also kept out (a low specificity for peanuts). You accept this trade-off because the consequences of a peanut sneaking in are severe (possible death) and the consequences of mistakenly excluding non-­peanut­-containing-­food are quite low (the child will just have to eat something else).

The consequences of missing a case of cervical cancer are all bad and include possible death from untreated cancer, but the consequences of a false-positive result on a Pap test are low- usually the patient is simply referred for an additional Pap test or some other diagnostic test. It's inconvenient for the patient, and may be distressing, but these consequences are considered acceptable by practically physicians and patients when weighed against the possibility of death from a missed case of cervical cancer. 

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Your Pap result

So what do you do when you get that ominous call “the Pap came back abnormal?” First of all,
don’t panic. Remember the Pap test is simply a screening test­ and most abnormal results are just false­ positives. As a screening test, the appropriate medical response to a positive (abnormal) test result is to undergo some kind of additional diagnostic testing. For most abnormal Pap results, the doctor will simply suggest repeating the Pap test sometime in the near future (3 to 12 months later). The doctor may also suggest testing for HPV infection (the cause of most cases of cervical cancer).

The results of Pap tests are reported using the Bethesda system. Crudely speaking, this means
your test result will come back “atypical”, “low grade”, or “high grade.” Your doctor will consider other clinical factors in her recommended course of action, but for most women, a finding of “atypical” or “low grade” triggers a recommendation of a follow­up Pap test. A finding of “high grade” may trigger a recommendation of a different kind of diagnostic test- ­ a colposcopy­ to ensure that you are indeed not in the process of developing cervical cancer.

If instead you get the more typical no­-call after your Pap test, you can relax­ -  you have tested
negative for cervical cancer. Remember to get re-­tested again in three to five years. And no, you don't need a Pap test every single year. If your doctor tries to give you one every single year, ask her why, and why she isn't following the current clinical practice guidelines. 

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