Pap Smear Enters the Molecular Age

By: Dr. Felix Martinez, Jr.

Dr. George Papanicolaou probably never envisioned how far his pap smear would evolve since his days at Weill Medical College of Cornell University in Ithaca, NY.  Dr. Papanicolaou was the first to report that uterine cancer could be diagnosed by means of a vaginal smear and introduced his low-cost, easily performed screening test for early detection of the cancerous and precancerous cells at a 1928 medical conference.  Gone are the days when a cervical swab was smeared on a slide followed by discarding the excess collection.  Now every part of a pap collection is important for the ancillary testing being performed on liquid based collections (LBC).

Cervical swabs contain nucleated cells from the patient as well as nuclear material from infecting organisms.  Evolving methodologies can now test the cervical scrapings using Nucleic Acid Amplification Testing (NAAT) originally developed by Polymerase Chain Reaction (PCR) technology.  PCR has provided a multitude of commercial applications in the life sciences and in vitro diagnostics by combining the unique attributes of being very sensitive and very specific while offering a great deal of flexibility.  With PCR, it is possible to isolate a particular DNA sequence and then amplify this sequence to extremely high copy numbers.  PCR was developed in 1983 by Kary Mullis and has become a common and often indispensable technique used in laboratories for a variety of applications earning Mullis the Nobel Prize in Chemistry in 1993.

The PCR process can be divided into three stages starting with Amplification (when the chain reaction occurs), followed by Leveling Off stage (chain reaction slows) and then Plateau (chain reaction stops).  Because PCR amplifies specific targeted regions, it can be used to study extremely small amounts of sample.  The medical use of this exciting technology has exploded in recent years with the development of new applications.  Wherever specific genes can be isolated and identified to provide clues to the cause or natural history of a disease, PCR has become the method of choice for obtaining a definitive diagnosis.  The flexibility in an application-specific variation of PCR makes it seem like there are as many ways to do a PCR reaction as there are researchers doing them.  The advantage of molecular testing over cultures includes the convenience of collection and elimination of the rigorous collection, transport and time sensitive parameters that cultures entail.

InCyte Pathology offers GC Chlamydia testing on Pap collections, initially with Roche and starting in April using the BD DIagnostics ProbeTec Qx amplified DNA assays with  BD Viper probe testing (the only CT and NG assays approved by the FDA for use with the SurePath Liquid-based Pap Test collections).  The BD Viper system is used to perform all the steps involved in the extraction and amplification of target DNA.  Viper technology offers a built in control that confirms all positive results using an alternative nucleic acid target to rule out false positives.  This occurs within a self contained microwell technology that minimizes the possibility of contamination.

Seventy to 90% of chlamydia infections in women are asymptomatic with the result being long term health problems can develop before the patient even knows she is at risk.  ACOG, the Centers for Disease Control and Prevention (CDC), and the US Preventive Services Task Force recommend annual screening for chlamydia of all sexually active women age 25 and younger, as well as other asymptomatic women at high risk for infection.  According to the National Center for Health Statistics (NCHS), chlamydia remains the most commonly reported STD in the US.  If not treated, up to 40% of women infected with chlamydia may develop pelvic inflammatory disease (PID), which can lead to ectopic pregnancy and infertility.