What are the appropriate laboratory tests for a patient suspected of having a herpes infection?

Laboratory Testing for Herpes Infections

For suspected genital herpes with active lesions, PCR (nucleic acid amplification testing) from swabs of vesicular or ulcerative lesions is the preferred diagnostic test, offering superior sensitivity and specificity compared to viral culture, with results available in approximately 2 hours and the ability to simultaneously type HSV-1 versus HSV-2. 1, 2

When to Obtain Laboratory Testing

Laboratory confirmation should always be obtained because clinical diagnosis alone leads to both false positive and false negative results. 1, 2 Specifically test patients with:

• Vesicular or ulcerative lesions on genitals, buttocks, or thighs 2
• Mucous or purulent vaginal discharge 2
• History of recurrent genital lesions 2
• Sexual contact with a confirmed HSV case 2
• Persistent dysuria after treatment for gonorrhea or nongonococcal urethritis 2

Optimal Sample Collection Technique

For vesicular lesions (highest yield):

• Open vesicles with a sterile needle 3, 1
• Collect vesicular fluid with cotton-wool or Dacron swab 3, 1
• Vigorously swab the base of the lesion to obtain epithelial cells 1, 2
• Detection rates reach 90% with viral culture and even higher with PCR 1, 2

For male urethral involvement:

• Clean the external urethral opening with saline-moistened swab 3, 2
• Retract the prepuce to avoid contamination 2
• Insert cotton-wool or Dacron swab 0.5-2 cm into the urethral meatus 3, 2

For female patients:

• Clean the introitus with sterile gauze 2
• Insert swab 0.5 cm into the urethra for urethral exudates 2
• For cervical samples, insert swab 2 cm into cervical canal 3, 2
• Collect from vaginal wall using cotton-wool or Dacron swab on aluminum shaft 3, 2

Testing Methods in Order of Preference

1. PCR (First-line test for active lesions):

• Superior sensitivity and specificity compared to all other methods 1, 2, 4
• Simultaneously detects and types HSV-1 vs HSV-2 in single reaction 1
• Results available in approximately 2 hours 1, 2
• Less strict transportation requirements than viral culture 1
• Should replace viral culture as the gold standard 4, 5

2. Viral Culture (Alternative when PCR unavailable):

• Significantly lower sensitivity than PCR, particularly for ulcerative lesions (70% detection) or crusting lesions (27% detection) 1
• Requires refrigeration during transport 1
• Material should not be kept more than 24 hours at room temperature 3
• HSV is sensitive to temperature and drying, so transportation failures dramatically reduce success 3

3. Antigen Detection (Immunofluorescence or Enzyme Immunoassay):

• Can be employed for symptomatic patients but less sensitive than PCR 1
• Sensitivity may drop to less than 50% when testing asymptomatic patients 3
• Most commercially available assays do not differentiate between HSV-1 and HSV-2 3

Type-Specific Serologic Testing

Use glycoprotein G-based type-specific serology (97% sensitivity, 98% specificity) for: 1, 2

• Asymptomatic individuals with history suggestive of genital herpes 2
• Patients with atypical presentations 1, 2
• When lesions have healed and PCR/culture was not obtained 2
• Evaluating discordant couples 2, 6
• Women who develop first clinical episode during pregnancy 6
• Asymptomatic pregnant women whose partners have history of genital herpes 6

Critical Pitfalls to Avoid

Do not rely on samples from crusted lesions - detection rates drop to 27% even with viral culture. 1 Sample early vesicular lesions for highest yield. 7

Never rely on Tzanck smears or cytological examinations (Papanicolaou smears) - they have low sensitivity and specificity and should not be used for diagnosis. 3, 1

Do not use HSV-specific IgM testing to diagnose recent infection - approximately one-third of patients with recurrent HSV-2 have IgM responses, making it a poor indicator of acute infection. 1

Do not skip type-specific testing - distinguishing HSV-1 from HSV-2 affects prognosis and counseling, so type-specific testing is always recommended. 4, 8

Differential Diagnosis Considerations

Always consider and test for other causes of genital ulceration: 2

• Treponema pallidum (syphilis) 2
• Haemophilus ducreyi (chancroid) 2
• Non-infectious causes: Crohn disease, Behçet syndrome, fixed drug eruption 2