I don’t want to disappoint you, but…….
We don’t need to be performing pelvic exams for the sole purpose of cervical sampling in women we suspect of having simple chlamydia or gonorrhea infections. Although we’ve been taught that women presenting for an STD check need a pelvic exam, the cervical swabs we obtain are entirely unnecessary.
Self-collected vulvovaginal swabs are performed by the patient, who is instructed to insert the swab in the vagina and rotate for roughly 10 seconds. This uses the same nucleic acid amplification testing (NAAT) swabs that we already use in the Emergency Department during pelvic exams. Rather than perform a pelvic exam – something that ties up nurses, physicians, and rooms – we can simply hand patients these swabs and quickly instruct them on how to perform the test.
But how do self-collected vulvovaginal swabs perform compared to physician-collected endocervical samples? One prospective study of 3859 women was performed comparing self-collected, vulvovaginal NAAT testing to an otherwise identical physician-collected endocervical sample.1,2 Patients were responsible for packaging the sample, which was then tested against the traditionally collected (pelvic exam) endocervical sample. Patients were considered ‘true positives’ if GC/Chlamydia NAAT was confirmed using an additional NAAT with a different nucleic acid target – the authors do not explain the characteristics of this test any more than that. There are issues with the last part of this methodology.*
However, since physician-collected endocervical sampling is effectively our ‘gold-standard’ in the ED, we really only care about one data point. That is, what sample technique found more GC/chlamydia infections that were ‘confirmed’ by a second NAAT assay – endocervical or vulvovaginal? The paper does effectively answer this question.
In the case of chlamydia, the sensitivity of self-collected vulvovaginal swabs was 97% (NPV 99.7) compared to 88% for physician-collected endocervical swabs (p<0.00001). Only 0.13% of samples were ‘indeterminate’, meaning there was some form of disagreement in the NAAT results.1 In the case of gonorrhea, the sensitivity of vulvovaginal swabs was 99% compared to 96% for endocervical swabs, (p=0.375).2
So what do these data mean? Self-collected, vulvovaginal testing produced essentially the same sensitivity characteristics in diagnosing gonorrhea infections. If you’re looking for gonorrhea, you’re equally likely to find it with an endocervical or vulvovaginal swab. In the case of chlamydia, however, vulvovaginal swabs actually revealed more infections than endocervical swabs. The authors conclude that endocervical samples missed 9% of chlamydia infections, or one out of every 11 infections. The authors hypothesize that this is due to chlamydia infections harbored in the urethra that are missed by endocervical sampling. Furthermore, the authors identified 12 previously published studies making similar comparisons to vulvovaginal and endocervical sampling in chlamydia. 10 of those found vulvovaginal swabs to be more sensitive (median 5.1% difference) while 2 of them found a higher sensitivity with endocervical samples (median 1.8% difference).1 If you’re looking for chlamydia, you’re more likely to find it with a vulvovaginal swab than with an endocervical swab.
Detroit Medical Center uses the BD ProbeTec Qx Amplified DNA assays. This is an NAAT assay similar to the one used in the studies outlined above. According to the manufacturer, this assay remains effective when the vulvovaginal self-collection technique is used.3 In fact, BD provides patient instructions for how to do so.4 Additionally, patients prefer this method of non-invasive testing, and 94% state that they’d be tested more often if a self-collected vaginal swab was used.5
In light of all of the above data, the CDC’s recommendations state:
For female screening, specimens obtained with a vaginal swab are the preferred specimen type. Vaginal swab specimens are as sensitive as cervical swab specimens, and there is no difference in specificity. Self-collected vaginal swabs are equivalent in sensitivity and specificity to those collected by a clinician. Cervical samples are acceptable when pelvic examinations are done, but vaginal swab specimens are an appropriate sample type, even when a full pelvic exam is being performed.6
Clearly, this doesn’t obviate the need for a pelvic exam in all patients. But for a patient with a history and symptoms suggestive of GC/chlamydia infection – or those patients who simply request an STD test and deny any bleeding or pain – the pelvic exam is an antiquated and unnecessary procedure.
Reid K Smith, M.D.
Sinai-Grace Emergency Medicine
- Schoeman SA, et. al. Assessment of best single sample for finding chlamydia in women with and without symptoms: a diagnostic test study. BMJ 2012; 345:e8013. PMC3520545.
- Stewart CM, et. al. Assessment of self taken swabs versus clinician taken swab cultures for diagnosing gonorrhea in women: single center, diagnostic accuracy study. BMJ 2012; 345:e8107.
- Fine, P, et. al. Vaginal swab performance on the BD Viper System with XTR technology (extracted mode) for detection of Chlamydia trachomatis and Neisseria gonorrhea at family planning/OB/GYN collection sites – perspectives in clinical care. Presented at 25th clinical virology symposium. Daytona Beach, FL, April 2009. Available at https://www.bd.com/ds/technicalCenter/whitepapers/lr222943.pdf.
- Available at https://www.bd.com/ds/technicalCenter/charts/ch_1_222801.pdf
- Chernesky, MA, et. al. Women find it easy and prefer to collect their own vaginal swabs to diagnose Chlamydia trachomatis or Neisseria gonorrhea infections. Sex Transm Dis. 2005 Dec;32(12):729-33. PMID 16314768.
- Rapp, JR et. al. Recommendations for the Laboratory-Based Detection of Chlamydia trachomatis and Neisseria gonorrhea. MMWR 2014; 63(RR02);1-19. Available at http://www.cdc.gov/mmwr/preview/mmwrhtml/rr6302a1.htm
* The primary issue with these studies is the use of the term ‘sensitivity.’ With a ‘gold-standard’ (although the authors rightfully avoid using the term), that is essentially a different version of the tested NAAT assay, these papers cannot really be used to make any population-based assumptions on GC/chlamydia testing/symptomatology. The authors do so anyway. In other words, when using two tests with similar characteristics in a population with very low disease prevalence, assigning a sensitivity to one of those tests is rather arbitrary – or, at least, it’s different than what we typically think of as ‘sensitivity’. In fact, the true sensitivity is really determined by the NAAT assay manufacturers. However, GC/chlamydia swabs are the prototypical screening test that doesn’t even require a confirmatory assay in practice. We desire higher sensitivity at nearly all costs. Always keep in mind that even high sensitivities begin to fail in populations with a low prevalence of disease. There are a lot of implications here – again, sensitivity is a misleading term if not understood correctly. The reality is that all of the above is purely academic for an ED practice, where we tend to treat prior to results – which are never reflexed to any confirmatory test.