What is the proper procedure for collecting a bacterial vaginosis (BV) swab?

Proper Procedure for Collecting a Bacterial Vaginosis (BV) Swab

To properly collect a bacterial vaginosis swab, use a cotton swab to collect vaginal secretions from the pooled vaginal discharge during speculum examination, then prepare samples for microscopic examination, pH testing, and whiff test to diagnose BV. 1

Equipment Needed

• Speculum
• Cotton swab
• pH paper
• Microscope slides
• Normal saline (0.9%)
• 10% Potassium hydroxide (KOH)
• Transport medium (if sending to laboratory)

Collection Procedure

Speculum Examination

• Insert speculum after completing external examination 1
• Lubricate speculum with warm water only (not lubricant) to facilitate insertion 1
• Insert speculum completely before opening the blades to minimize discomfort 1
• Visualize the vaginal walls and cervix, noting any discharge or lesions 1

Swab Collection

• Use a cotton swab to collect vaginal secretions from the pooled vaginal discharge or lateral vaginal walls 1
• Avoid contaminating the swab with cervical mucus as this may affect test results 1
• Collect sufficient material to perform necessary diagnostic tests 1

Diagnostic Testing for BV

Point-of-Care Testing

• Prepare samples for the following tests to diagnose BV according to Amsel criteria (requires 3 of 4 criteria) 1:

1. pH Testing:

   • Dip pH paper in the secretions left on the speculum tip after removal 1
   • Read the color change within 10 seconds 1
   • BV typically has pH >4.5 1

2. Wet Mount Preparation:

   • Place vaginal secretions from swab in 0.5-1 mL of saline 1
   • Apply to microscope slide and cover with slip 1
   • Examine under microscope for "clue cells" (epithelial cells covered with bacteria) 1

3. Whiff (Amine) Test:

   • Mix vaginal secretions with 10% KOH on a slide 1
   • A positive test produces a characteristic "fishy" odor 1

4. Discharge Characteristics:

   • Note if discharge is homogeneous, white, and adherent to vaginal walls 1

Laboratory Testing

• If sending to laboratory, place swab in appropriate transport medium 1
• Transport time considerations:
  • For wet mount: optimal within 30 minutes, maximum 2 hours 1
  • For Gram stain: stable up to 12 hours at room temperature 1
  • For DNA hybridization probe: stable up to 7 days at room temperature 1

Alternative Diagnostic Methods

• Gram Stain (Nugent Criteria): More objective method for BV diagnosis with scoring of bacterial morphotypes 1, 2
• DNA Hybridization Probe: Commercial tests available that detect Gardnerella vaginalis and other BV-associated organisms 1
• Molecular Testing: Newer nucleic acid amplification tests (NAATs) provide objective results and can detect fastidious bacteria 1, 3

Common Pitfalls to Avoid

• Using lubricant on the speculum (interferes with microscopic examination) 1
• Collecting cervical rather than vaginal specimens (incorrect site) 1
• Delaying microscopic examination (reduces sensitivity for detecting motile organisms) 1
• Failing to perform all diagnostic tests (pH, wet mount, whiff test) 1
• Not maintaining proper transport conditions if sending to laboratory 1

Clinical Significance

• BV is the most common cause of vaginal discharge in reproductive-age women 3, 4
• Proper diagnosis is important as BV is associated with adverse pregnancy outcomes and increased risk of STI acquisition 5, 4
• More than half of women with BV may be asymptomatic, highlighting the importance of proper testing technique 5