The Papanicolaou test (also called Pap smear, Pap test, cervical smear, or smear test) is a screening test used in gynecology to detect premalignant and malignant processes in the ectocervix. Significant changes can be treated, thus preventing cervical cancer. The test was invented by and named after Georgios Papanikolaou, but was also independently invented by Aurel Babeş.
In taking a Pap smear, a tool is used to gather cells from the outer opening of the cervix (Latin for "neck") of the uterus and the endocervix. The cells are examined under a microscope to look for abnormalities. The test aims to detect potentially pre-cancerous changes (called cervical intraepithelial neoplasia (CIN) or cervical dysplasia), which are usually caused by sexually transmitted human papillomaviruses (HPVs). The test remains an effective, widely used method for early detection of pre-cancer and cervical cancer. The test may also detect infections and abnormalities in the endocervix and endometrium.
It is generally recommended that females who have had sex seek regular Pap smear testing. Guidelines on frequency vary, from annually to every five years. If results are abnormal, and depending on the nature of the abnormality, the test may need to be repeated in three to twelve months. If the abnormality requires closer scrutiny, the patient may be referred for detailed inspection of the cervix by colposcopy. The patient may also be referred for HPV DNA testing, which can serve as an adjunct to Pap testing.
Abnormal results are reported according to the Bethesda system. They include:
The sample is stained using the Papanicolaou technique, in which tinctorial dyes and acids are selectively retained by cells. Unstained cells cannot be visualized with light microscopy. The stains chosen by Papanicolaou were selected to highlight cytoplasmic keratinization, which actually has almost nothing to do with the nuclear features used to make diagnoses now.
The sample is then screened by a specially trained and qualified cytotechnologist using a light microscope. The terminology for who screens the sample varies according the country; in the UK, the personnel are known as Cytoscreeners, Biomedical scientists (BMS), Advanced Practitioners and Pathologists. The latter two take responsibility for reporting the abnormal sample which may require further investigation.
Studies of the accuracy of conventional cytology report:
In the United States, physicians who fail to diagnose cervical cancer from a pap smear have been convicted of negligent homicide. In 1988 and 1989, Karen Smith had received pap smears which were argued to have "unequivocally" shown that she had cancer; yet the lab had not made the diagnosis. She died on March 8 1995. Later, a physician and a laboratory technician were convicted of negligent homicide. These events have led to even more rigorous quality assurance programs, and to emphasizing that this is a screening, not a diagnostic, test, associated with a small irreducible error rate.
Studies of the accuracy of liquid based monolayer cytology report:
Some, but not all studies, report increased sensitivity from the liquid based smears.
By adding the more sensitive HPV Test, the specificity may decline. However, the drop in specificity is not definite. If the specificity does decline, this results in increased numbers of false positive tests and many women who did not have disease having colposcopy and treatment. A worthwhile screening test requires a balance between the sensitivity and specificity to ensure that those having a disease are correctly identified as having it and equally importantly those not identifying those without the disease as having it. Due to the liquid based pap smears having a false negative rate of 15-35%, the American College of Obstetricians and Gynecologists and American Society for Colposcopy and Cervical Pathology have recommended the use of HPV testing in addition to the pap smear in all women over the age of 30.
Regarding the role of HPV testing, randomized controlled trials have compared HPV to colposcopy. HPV testing appears as sensitive as immediate colposcopy while reducing the number of colposcopies needed. Randomized controlled trial have suggested that HPV testing could follow abnormal cytology or could precede cervical cytology examination.
A study published in April 2007 suggested the act of performing a Pap smear produces an inflammatory cytokine response, which may initiate immunologic clearance of HPV, therefore reducing the risk of cervical cancer. Women who had even a single Pap smear in their history had a lower incidence of cancer. "A statistically significant decline in the HPV positivity rate correlated with the lifetime number of Pap smears received.
The endocervix may be partially sampled with the device used to obtain the ectocervical sample, but due to the anatomy of this area, consistent and reliable sampling cannot be guaranteed. As abnormal endocervical cells may be sampled, those examining them are taught to recognize them.
The endometrium is not directly sampled with the device used to sample the ectocervix. Cells may exfoliate onto the cervix and be collected from there, so as with endocervical cells, abnormal cells can be recognised if present but the Pap Test should not be used as a screening tool for endometrial malignancy.