What specimen should be requested for a gram stain in a patient presenting with vaginal discharge?

Specimen for Gram Stain in Vaginal Discharge

For Gram stain evaluation of vaginal discharge, request a swab of vaginal discharge collected from the vaginal walls, placed directly into a transport swab tube, stable at room temperature for up to 12 hours. 1

Optimal Specimen Collection

• Collect the specimen using a vaginal swab from the lateral vaginal walls or pooled vaginal discharge 2, 3
• Avoid contamination with cervical mucus, as this affects test accuracy 3
• Place the swab directly into a transport swab tube (such as Culturette, Eswab, or similar product) immediately after collection 1

Transport and Timing Requirements

• The specimen remains stable at room temperature for 12 hours, allowing reasonable flexibility for transport to the laboratory 1, 2
• Do not refrigerate or freeze the specimen 1
• Ensure the swab is placed in the transport tube immediately to prevent drying 1

Clinical Context: Why Gram Stain Matters

The quantitative Gram stain (Nugent criteria) is the gold standard and most specific procedure for diagnosing bacterial vaginosis, evaluating the relative concentration of bacterial morphotypes in vaginal fluid 1, 2. This method:

• Identifies normal flora showing predominance of large gram-positive rods (Lactobacillus) 2
• Detects BV by showing mixed flora with decreased or absent Lactobacillus morphotypes and presence of Gardnerella vaginalis and other BV-associated organisms 2
• Provides superior specificity compared to DNA probe tests, point-of-care tests, or culture that only detect G. vaginalis presence 1

Critical Pitfalls to Avoid

• Never culture for Gardnerella vaginalis alone, as it can be present in normal vaginal flora and is not specific for BV diagnosis 2
• Do not delay transport beyond 12 hours, as bacterial morphology may deteriorate 1
• Ensure the laboratory uses standardized Nugent scoring criteria (0-10 scale) for consistent interpretation 2, 4
• If wet mount examination is also requested, collect a separate swab in 0.5 mL saline, as this specimen must be examined within 2 hours and has different transport requirements 1

Complementary Testing Considerations

While Gram stain is optimal for bacterial vaginosis diagnosis, consider ordering:

• Vaginal pH measurement (BV typically shows pH >4.5, while yeast shows pH <4.5) 1, 2
• NAAT testing for Trichomonas vaginalis, Chlamydia trachomatis, and Neisseria gonorrhoeae using the same vaginal swab collection device, stable at room temperature for up to 7 days 1, 3
• Culture for yeast if recurrent infections are suspected, to identify non-albicans Candida species requiring different treatment 1, 5