What is the appropriate evaluation and treatment for a female patient presenting with yellow vaginal discharge, considering potential causes such as sexually transmitted infections (STIs) or bacterial vaginosis (BV)?

Yellow Vaginal Discharge: Evaluation and Treatment

Yellow vaginal discharge requires immediate point-of-care testing to differentiate between trichomoniasis (which presents as yellow-green, frothy discharge), bacterial vaginosis, and cervical infections—with trichomoniasis being the most likely cause of specifically yellow discharge and requiring oral metronidazole treatment of both patient and partner. 1

Immediate Diagnostic Approach

Point-of-Care Testing (Perform in This Order)

• Measure vaginal pH using narrow-range pH paper: pH >4.5 indicates trichomoniasis, bacterial vaginosis, or cervical infection; pH <4.5 suggests candidiasis (though candidiasis typically causes white, not yellow discharge). 2, 3

• Perform whiff test with 10% KOH: A positive fishy odor indicates bacterial vaginosis or trichomoniasis. 2, 3

• Prepare saline wet mount immediately: Look for motile trichomonads (trichomoniasis) and clue cells (bacterial vaginosis). 2, 3

• Prepare KOH mount: Examine for yeast or pseudohyphae to rule out candidiasis, though this is unlikely with yellow discharge. 2, 3

Essential Laboratory Testing

• NAAT for Trichomonas vaginalis is mandatory—wet mount sensitivity is only 40-80%, so clinical suspicion requires molecular testing even if wet mount is negative. 2

• NAAT for Neisseria gonorrhoeae and Chlamydia trachomatis to evaluate for cervical infections causing mucopurulent cervicitis, which presents as yellow endocervical discharge. 1, 2

• Consider Gram stain with Nugent criteria if bacterial vaginosis diagnosis remains equivocal after initial testing. 2

Most Likely Diagnoses Based on Yellow Discharge

Trichomoniasis (Primary Consideration)

• Presents with copious, yellow-green, frothy discharge with foul or fishy odor, pH >4.5, and motile trichomonads on wet mount. 1, 2

• Treatment: Oral metronidazole with cure rates of 90-95%. 1

• Critical management point: Treat sex partners simultaneously and instruct patients to avoid sex until both partners complete treatment—partner treatment significantly increases cure rates. 1

• Follow-up is unnecessary if symptoms resolve after treatment. 1

Mucopurulent Cervicitis

• Characterized by yellow endocervical exudate visible in the endocervical canal, often caused by N. gonorrhoeae or C. trachomatis. 1

• May be asymptomatic or present with abnormal vaginal discharge and post-coital bleeding. 1

• Treatment approach: If prevalence of both gonorrhea and chlamydia is high in your patient population, treat empirically for both infections. If only chlamydia prevalence is substantial, treat for chlamydia alone. 1

• Partners require the same treatment as the index patient if treated presumptively. 1

Bacterial Vaginosis (Less Likely for Yellow Discharge)

• Typically presents with thin, gray-white discharge (not yellow), but may appear tan when mixed with blood. 2, 3

• Characterized by fishy odor, pH >4.5, and clue cells on microscopy. 1, 2

• Treatment: Metronidazole 500 mg orally twice daily for 7 days or clindamycin cream. 1, 2

• Partner treatment is not beneficial for preventing BV recurrence. 1

Special Populations

Pregnant Women

• Trichomoniasis in pregnancy is associated with premature rupture of membranes, preterm delivery, and low birth weight—symptomatic pregnant women should be treated with oral metronidazole. 1

• Bacterial vaginosis in pregnancy requires treatment in all symptomatic women, with follow-up evaluation one month after treatment completion to verify effectiveness due to adverse pregnancy outcomes. 1

HIV-Infected Patients

• Patients with HIV infection should receive identical treatment regimens as HIV-negative patients for all vaginal infections. 1

Critical Pitfalls to Avoid

• Do not rely on wet mount alone for trichomoniasis diagnosis—the 40-80% sensitivity means you will miss many cases without NAAT testing. 2

• Do not assume yellow discharge is always infectious—in sexually active young women at risk for STIs, mucopurulent cervicitis from gonorrhea or chlamydia must be ruled out. 1

• Do not treat empirically without considering local STI prevalence—if both patient compliance and STI prevalence are low, await test results rather than overtreat. 1

• Do not forget partner treatment for trichomoniasis—cure rates increase significantly when partners are treated simultaneously. 1