An update on diagnosing STIs and HIV

May 01, 2005

We can do a better job of screening and testing sexually active teens and young adults for STIs. Keeping up with the latest evidence can help you decide when to test, whom to test, and which of a wide array of office- and lab-based tests to choose.

Accurately diagnosing sexually transmitted infections (STIs) remains a cornerstone of caring for adolescents and young adults. Given the many techniques and approaches now available, it's getting more challenging than ever for clinicians to screen and test appropriately. For example, although screening asymptomatic teenagers during routine gynecologic exams is recommended, relatively few physicians actually do so.1 Female physicians are more likely to screen than male physicians and obstetrician/gynecologists are more likely than other primary care physicians to screen women.2,3 However, this rate-which varies by disease, with a maximum of 54.3% for chlamydia in nonpregnant women and 84.6% in pregnant women-remains far below screening recommendations.4

In addition, many physicians feel that their counseling on the topic of STIs is ineffective.5 Interestingly, in a recent survey of physicians who tested for gonorrhea or chlamydia, up to 41% never used nucleic acid amplification tests (NAATs), rather than urine-based DNA amplification techniques.3 These data confirm an ongoing clinical issue: How do we incorporate new technology into clinical practice? Our goal here is to describe both the traditional and latest methods for diagnosing a variety of STIs.

Diagnostic methodologies for bacterial vaginosis Traditional diagnostic methods include microscopic methods and culture; DNA/RNA-based methods are another option.

Amsel's criteria require three of the following four signs at speculum exam and wet mount: the presence of clue cells, homogeneous discharge that adheres to the vaginal walls, pH of vaginal fluid greater than 4.5, and a "fishy" odor detected following the addition of 10% hydrogen peroxide (the whiff test).8 Thomason's modification of Amsel's criteria includes 20% or more clue cells, with two of the other three criteria.9 Finally, Nugent's method uses weighted quantities of three morphotypes of bacteria found on vaginal Gram's stain.10 Most of these criteria for establishing the diagnosis of BV yield good sensitivity (90% to 100%) and specificity (86% to 97%).11-13

The isolation of G vaginalis in vaginal culture, although sensitive, is not specific, and does not correlate with clinical symptomatology.11

DNA/RNA-based diagnostic methods. Office-based tests such as microscopy, pH, and the whiff test are underutilized in evaluating vaginitis. There are several methods available, including Affirm VP (Becton Dickinson), FemExam (CooperSurgical), and Proline IminoPeptidase (PIP) Activity Test (Litmus Concepts).4 Affirm VP can detect and differentiate DNA from G vaginalis, Candida spp., and Trichomonas vaginalis; sensitivity was 90.5% and specificity 97.3% for Affirm VP, when compared to the presence of clue cells and 93.6% and 81.4% when compared to Nugent criteria.14 FemExam is a two-card system. The first card detects an elevated vaginal pH and the presence of trimethylamine, and the second detects the activity of aminopeptidase through the Pip Activity Test, which signifies the presence of G vaginalis. In clinical situations, compared to the Nugent score, the first card has a sensitivity of 71.4% and a specificity of 72.8%, while the second card has a sensitivity of 70% and specificity of 81.0%. The combination of both cards reveals a sensitivity of 91.0% and a specificity of 61.5%.15 Although these newer diagnostic methods are both sensitive and specific and provide potential alternative diagnostic methodologies for BV, they have not made their way into routine clinical practice.

Diagnostic methods for Chlamydia trachomatis Methods include the traditional culture, antibody-based detection methods, and DNA/RNA-based ones.