Trichomoniasis Workup

Updated: Sep 19, 2017
  • Author: Darvin Scott Smith, MD, MSc, DTM&H; Chief Editor: Michael Stuart Bronze, MD  more...
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Approach Considerations

Given the poor reliability of history and physical findings, diagnosis of trichomoniasis depends on laboratory testing. According to the CDC, providers should obtain laboratory tests in all women seeking care for vaginal discharge and women at high risk of sexually transmitted infection. [9]

Tests for trichomoniasis are quick and can be performed in the medical office. [56] Self-testing has also been proposed but is not currently approved by the US Food and Drug Administration (FDA). [57] The basic office evaluation includes tests to exclude other possible causes of the patient’s complaints. Because T vaginalis infection is strongly associated with the presence of other STIs, [39] providers should test for other STIs, including gonorrhea, chlamydia, syphilis, HIV infection, hepatitis B, and hepatitis C. In multiple studies, the majority of women with T vaginalis infections were also found to have bacterial vaginosis. [58, 59, 39]


Standard Laboratory Studies

Saline wet mount evaluation

In women, vaginal trichomoniasis has historically been diagnosed by wet mount microscopy. Saline wet mount evaluation is performed by placing a small amount of vaginal discharge on a microscope slide and mixing with a few drops of saline solution. The slide is then examined under a microscope at low or medium power (see the video below).

Trichomonas vaginalis on a saline wet mount at 40X on the microscope. Several motile parasites transit through the field, surrounded by white blood cells and squamous epithelial cells.

The presence of flagellated pyriform protozoa, or trichomonads, indicates a positive test result. These ovoid-shaped parasites are slightly larger than polymorphonuclear leukocytes (PMNs), a type of white blood cell, and may be identified by their ameboid mobility. Trichomonads cause an inflammatory reaction; therefore, a large number of PMNs are usually present and correlate with the severity of infection.

Slides must be read immediately after collection. [6] Kingston et al [60] looked at samples that were positive for trichomonads on initial reading and then reevaluated them every 10 minutes. At 10 minutes, 20% of samples became negative; by 30 minutes, 35% were negative; and by 2 hours, 78% had become negative.

It is important to note that microscopy has a low sensitivity (estimated at 50-70%) in the detection of T vaginalis in vaginal secretions and is not the criterion standard technique for trichomoniasis diagnosis. [7, 8, 6] Because they involve the direct visualization of the trichomonads, wet mounts are more likely to be positive in women with high organism loads. [2] The absence of trichomonads on microscopy does not rule out a diagnosis of vaginal trichomoniasis.

Despite their limitations, wet mounts are frequently used, because they are quick, cheap, and easy to perform.

The relatively poor sensitivity of saline wet mount evaluation may be increased somewhat by using cervical vaginal lavage. [61] In one study, sensitivity was increased to 74.4% using the cervical vaginal lavage technique versus 54.7% vaginal swab alone. [61]

Wet mount microscopy is not an effective test for the diagnosis of trichomoniasis in men.

A short downloadable video illustrating this test is available from the Seattle STD/HIV Prevention Training Center. [62]

Standard culture

Culture is the current criterion standard for trichomoniasis diagnosis. Providers should perform T vaginalis cultures when the suspicion of trichomoniasis is high but saline wet mount evaluation does not reveal the protozoan. Culture may also be useful as diagnostic screening for high-risk populations. [11] Culture is more sensitive and specific than microscopy. [6, 63] In a study by Wolner-Hanssen et al, 35.6% of trichomoniasis cases were detected by culture and not by wet mount or Papanicolaou (Pap) smear. [39]

A swab is put in broth and incubated anaerobically at 37°C. Growth is usually detected within 48 hours, and samples without growth after 7 days are considered negative for trichomoniasis. [63]

In addition to improved diagnostic value, an advantage of culture is delayed inoculation. Swab specimens may sit for some time prior to inoculation, allowing for the reading of a wet mount prior to pouch inoculation. [64] Another advantage of culture is that swab specimens may be obtained by the patient (self-obtained specimens), a technique useful with adolescents and in resource-poor settings. [11] Culture has also been demonstrated to be useful in individuals with suspected resistant trichomoniasis. Physicians can determine whether trichomonads are the cause of the vaginitis and can obtain the susceptibility of the strain.

Culture is especially important for diagnosing trichomoniasis in men, in whom wet mount preparations are particularly unreliable. Urethral swab, urine, and semen cultures are used to maximize sensitivity. [6] The CDC does not recommend oral and rectal testing, as infection rates at these sites appear to be low. [9]

Disadvantages of the culture method include testing time and availability. [21]

InPouch TV Culture System

The InPouch TV Culture System (Biomed, White City, Ore), a combined wet mount and culture kit, is commonly used and readily available. This test kit has a sensitivity of 81-100%. [65] It may detect as little as 1 parasite in the sample. Samples taken during menses are not adversely affected.

The clinician inoculates the upper chamber of the pouch with a cotton swab. The pouch can be kept at room temperature for up to 18 hours without significant alteration of sensitivity. In the laboratory, a viewing clamp is placed across the upper chamber and examined under a microscope at a magnification of 100. If no trichomonads are viewed, the bottom chamber is inoculated by using the medium from the upper chamber. The InPouch is incubated at 37°C and viewed at regular intervals.

Papanicolaou smear

Trichomonads may be viewed on Pap smear, but this test yields low sensitivity and should not be relied on for diagnosis of T vaginalis infection. The sensitivity of Pap smear for detecting trichomonads is 40-60%. [66, 67] Specificity approaches 95% in the hands of trained technicians. [68] False-positive results are also common with this technique. [21]

pH testing

Vaginal pH may be determined by touching a swab containing vaginal secretions to pH indicator paper. A normal pH practically excludes the diagnosis of trichomoniasis. A pH greater than 4.5 is usually found with trichomoniasis. [44] However, an elevation in pH is not specific for trichomoniasis. Bacterial vaginosis frequently also elevates vaginal pH. [6]

Whiff test (amine odor test)

Perform the whiff test (amine odor test) by adding several drops of 10% potassium hydroxide to a sample of vaginal discharge. A strong fishy odor is indicative of a positive test result. Such a result may suggest either trichomoniasis or bacterial vaginosis. Thus, the whiff test should not be considered an accurate means of diagnosing trichomoniasis. It is 1 of the 4 parts of the Amsel criteria used [69] to diagnose bacterial vaginosis.

The whiff test is now combined with vaginal pH on a single card, the FemExam pH and Amines TestCard. On this card, the pH paper color change and the odor test are replaced with plus or minus signs.


Molecular Techniques for Detecting Antigen, DNA, or RNA

Two FDA-approved tests are currently available for diagnosing trichomoniasis in women: (1) the OSOM Trichomonas Rapid Test (an antigen-based test; Genzyme Diagnostics, Cambridge, Mass) and (2) the Affirm VP III Microbial Identification Test (a DNA probe; BD Diagnostic Systems, Sparks, Md). [6, 70] Both tests have a sensitivity greater than 83% and a specificity greater than 97% for detecting T vaginalis in vaginal secretions, according to the CDC. [9]

The OSOM Trichomonas Rapid Test uses color immunochromatographic “dipstick” technology with murine monoclonal antibodies. Results are read within 10 minutes. Freezing and transportation of specimens do not appreciably alter the test results. In a comparison with a composite reference standard of wet mount microscopy and culture, Huppert et al found the sensitivity of the OSOM test to be 83.3% and the specificity 98.8%. [71] A second study by Huppert et al found a sensitivity of 82% in comparison with a composite reference standard of wet mount, culture, rapid antigen testing, and polymerase chain reaction (PCR). [72] A third study compared the OSOM test to a composite reference standard for which a positive sample was defined as one that was positive by any combination of wet mount, Aptima ATV assay, or OSOM test. The prevalence of infection in the population tested was low, at 2%. The sensitivity was 94.7%, and the specificity was 100%. [73]

The Affirm VPIII Microbial Identification Test detects the presence of Trichomonas, Gardnerella, and Candida species by using direct hybridization technology. Its sensitivity is 90-100%, [74] and the detection threshold is reported to be 5000 trichomonads/mL. Results from the Affirm VPIII test take about 45 minutes.

A bulletin on proper preparation and testing of specimens is available from the manufacturer. Specimens for which testing is expected to be delayed for more than 1 hour at ambient temperature or 4 hours with refrigeration should be stored in the Affirm VPIII Ambient Temperature Transport System (ATTS) for up to 72 hours. [75] In a study by Hollman et al, no difference was noted in detection of T vaginalis in urine samples compared with vaginal swabs. [76]

The APTIMA Trichomonas vaginalis ATV Assay (Gen-Probe, San Diego, Calif) uses nucleic acid hybridization technology to detects the presence of T vaginalis. [6, 70] Sensitivity is 74-98% and specificity is 87-98%. [33] One study reported decreased sensitivity for tests performed on first-void urine specimens in male patients. [74] The sample is run on a proprietary processing system capable of running about 1000 samples per day. Expected turnaround time is about 1-2 days. Currently, the APTIMA Combo2 assay is FDA-approved for the diagnosis of chlamydia and gonorrhea, so laboratories using this technology may wish to add the T vaginalis assay to their existing technology.

PCR methods yield a high sensitivity (84%) and specificity (94%). [77, 78] PCR is based on DNA amplification and detection using known primers to TV genes. Because no approved PCR tests are available for general use, this approach is limited to research studies. Sensitivities of PCR tests for T vaginalis have been reported at 85-100%. [2, 79, 80] Amplicor, an FDA-approved PCR assay for gonorrhea and chlamydia modified to detect T vaginalis, was found to have a sensitivity of 88-97% and specificity of 98-99%. [81] Some researchers have suggested that PCR has great diagnostic potential, [21] particularly in men, while others maintain it offers little advantage over culture. In men, performing PCR on urine sediment rather than urethral swabs may improve detection rates. [82]

Direct fluorescent antibody (DFA) staining is more sensitive than saline wet mount but less sensitive than culture. DFA allows rapid diagnosis but requires a trained microscopist and a fluorescent microscope.


Histologic Findings

Trichomonads may be observed in a saline wet mount of a vaginal swab or secretion in approximately 60-70% of women with trichomoniasis. [6] Trichomonads are ovoid in shape and approximately the size of a white blood cell (WBC)—about 10-20 μm long and 2-14 μm wide. They are identifiable by their ameboid mobility. A trichomonad has 4 flagella projecting from the anterior portion of the cell and 1 flagellum extending backward to the middle of the organism, forming an undulating membrane. An axostyle, a rigid structure, extends from the posterior aspect of the organism. [10, 2] Because trichomonads cause an inflammatory reaction, a large number of white blood cells are usually present, correlating with the severity of the infection.