Detects IgM antibodies specific to: HSV-1: Commonly causes oral herpes (cold sores)
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HSV-1 IgM Test Information Guide
Herpes Simplex Virus I (HSV)-IgM
Why is it done?
Detects IgM antibodies produced during primary or acute HSV-1 infection
Identifies newly acquired HSV-1 infection to differentiate from recurrent infections
Diagnoses acute herpes simplex keratitis, gingivostomatitis, or encephalitis
Confirms HSV-1 as causative agent in patients with acute clinical symptoms
Performed during early phase of infection when IgM antibodies are present (typically within first 2 weeks)
Assists in epidemiological tracking and outbreak investigations
Normal Range
Normal Result: Negative or <1.10 Index Value (varies by laboratory)
Positive Result: ≥1.10 Index Value or positive antibody titer (indicates recent or primary infection)
Units of Measurement: Index Value (S/CO) or Antibody Titer ratio; expressed as negative/positive or numerical index
Borderline/Equivocal Range: 0.90-1.10 Index Value may require repeat testing or confirmation with HSV-2 IgM
Normal (Negative) means: No detectable IgM antibodies; no evidence of acute or recent primary HSV-1 infection
Abnormal (Positive) means: IgM antibodies detected; suggests acute primary HSV-1 infection or early reactivation
Interpretation
Positive IgM Result: Indicates primary or acute HSV-1 infection; patient is in early phase of infection with active viral replication; typical presentation includes fever, oral ulcers, pharyngitis, or vesicular rash
Negative IgM Result: No acute or recent primary HSV-1 infection detected; patient either uninfected, has chronic/latent infection, or test performed after IgM window closes (>3-4 weeks post-infection)
IgM Positive + IgG Negative: Strong evidence of primary HSV-1 infection; first episode with no prior exposure
IgM Positive + IgG Positive: May indicate recurrent infection or reactivation; however, IgM can persist or be reactivated with HSV reactivation
IgM Negative + IgG Positive: Chronic or latent HSV-1 infection; previous exposure with immunity; recurrent infection not currently acute
Factors Affecting Results:
• Timing of blood draw relative to symptom onset (IgM typically present 1-2 weeks after infection onset)
• Cross-reactivity with HSV-2 possible with some assays
• Immunocompromised patients may have delayed or absent IgM response
• False positives rare but possible with certain laboratory methods
• Pregnancy status may affect interpretation in context of maternal-fetal transmission
Clinical Significance: Positive result warrants antiviral therapy initiation; important for differentiating acute from recurrent infection; critical in neonatal cases to guide treatment decisions
Associated Organs
Primary Organ Systems:
• Integumentary system (skin): Vesicular rash, ulcerations
• Oral cavity and pharynx: Gingivostomatitis, pharyngitis
• Mucous membranes: Genital, oral, and ocular lesions
• Nervous system: Encephalitis, meningitis
• Ocular system: Keratitis, conjunctivitis
Diseases Diagnosed/Monitored:
• Primary herpes simplex infection
• Acute herpetic keratitis
• Aseptic meningitis/encephalitis caused by HSV-1
• Erythema multiforme triggered by HSV-1
• Atypical presentations of HSV-1
Potential Complications/Risks of Acute Infection:
• Severe systemic infection in immunocompromised patients
• HSV encephalitis (high mortality if untreated)
• Disseminated disease in neonates or immunocompromised patients
• Secondary bacterial superinfection of lesions
• Permanent corneal scarring from untreated keratitis
• Chronic pain and post-herpetic neuralgia
• Vertical transmission risk during pregnancy/delivery
Follow-up Tests
Recommended Additional Testing:
• HSV-1 IgG antibody: To assess for chronic infection and immunity
• HSV-2 IgM/IgG: To differentiate between HSV-1 and HSV-2 infection
• HSV culture or PCR: For direct viral detection and typing confirmation
• Direct Fluorescent Antibody (DFA) testing: For rapid HSV identification
• Tzanck smear: For cytological confirmation of HSV infection
When CNS Involvement Suspected:
• CSF HSV-1 PCR (gold standard for HSV encephalitis)
• Lumbar puncture with cerebral spinal fluid analysis
• Brain MRI or CT imaging
• EEG if seizures or altered mental status present
When Ocular Infection Suspected:
• HSV-1 PCR from ocular specimens
• Ophthalmologic examination
• Slit-lamp examination for corneal involvement
When Neonatal Infection Suspected:
• HSV-1/2 PCR from neonatal blood, CSF, and swabs
• Maternal HSV serology
• Neonatal HSV-1 IgM (though often negative in neonates)
Monitoring Frequency:
• IgM testing valid only during acute phase (first 2-4 weeks); repeat testing after acute phase generally not useful
• IgG testing recommended 2-4 weeks after initial testing if primary infection suspected
• For immunocompromised patients: Consider HSV PCR for ongoing monitoring
Related/Complementary Tests:
• HSV-1 PCR (provides rapid confirmation)
• HSV-1/2 IgG by Western blot (reference standard)
• Nucleic acid amplification testing (NAAT)
• Viral culture (confirmatory but slower)
• Bacterial culture of lesions (to rule out secondary infection)
Fasting Required?
Fasting Requirement: No
Fasting Duration: Not applicable; fasting is not required for HSV-1 IgM serology
Special Instructions:
• No special dietary restrictions
• No fasting period required
• Standard blood draw procedures apply
Medications to Avoid:
• No specific medications need to be held for this test
• Antiviral medications (acyclovir, valacyclovir) do not interfere with antibody detection
• Continue all regular medications as prescribed
Patient Preparation:
• Inform healthcare provider of acute symptoms timing
• Report any current medications including antivirals
• Notify clinician if immunocompromised
• No special preparation needed beyond standard blood draw procedures
• Timing of test important: preferably within first 2 weeks of symptom onset
Sample Collection:
• Standard serum sample via venipuncture (5-10 mL)
• Allow blood to clot completely
• Separate serum into sterile tube
• Label with patient identification and collection date/time
• Room temperature storage acceptable for short periods
• Refrigerate if delay anticipated