What tests are performed to detect toxoplasmosis, Epstein‑Barr virus (EBV), and cytomegalovirus (CMV)?

Diagnostic Testing for Toxoplasmosis, EBV, and CMV

For toxoplasmosis, order IgG and IgM serology initially, with confirmatory testing at a reference laboratory if IgM is positive; for CMV and EBV, use quantitative nucleic acid testing (QNAT/PCR) on whole blood or plasma as the primary diagnostic method, supplemented by serology when needed.

Toxoplasmosis Testing

Initial Serologic Testing

• Start with IgG and IgM antibodies from peripheral blood 1
• Commercial laboratories can perform initial screening, but critical caveat: approximately 60% of positive IgM results from non-reference laboratories represent either false-positives (20%) or chronic infections (40%) rather than acute infection 1

Reference Laboratory Confirmation

When IgM is positive or equivocal, always send to a reference laboratory for comprehensive testing including 1:

• Toxoplasma IgG dye test
• Toxoplasma IgM ISAGA (immunosorbent agglutination assay) - more sensitive than standard ELISA
• Toxoplasma IgA ELISA

The IgM ISAGA test performed at reference laboratories is significantly more sensitive than commercial ELISA tests; a negative commercial IgM ELISA cannot exclude congenital toxoplasmosis 1.

PCR Testing for Fetal/Congenital Infection

When maternal infection is confirmed:

• Amniotic fluid PCR at ≥18 weeks gestation (10 mL specimen) 1
• Neonatal testing: PCR on blood, urine, and CSF plus serology 1
• Ship amniotic fluid on wet ice (2-8°C); CSF/tissue frozen on dry ice 1

Timing Considerations

IgM antibodies can persist beyond 1 year in low titers, making timing of infection difficult to determine without additional reference laboratory testing 1.

CMV Testing

Primary Diagnostic Method: QNAT/PCR

Quantitative nucleic acid testing is the gold standard for CMV monitoring 2:

• Use whole blood or plasma - both are equally suitable, though whole blood tends to show higher viral loads 2
• Whole blood demonstrates higher sensitivity for detection (similar detection rates to plasma but more sensitive overall) 3
• International standardization allows results reported in IU/mL, with interassay variability typically <0.5 log 2

Sample Selection

• Whole blood is preferred for maximum sensitivity in transplant monitoring 3
• Plasma is an acceptable alternative, particularly for CMV where correlation between sample types is strong (r=0.688) 3
• Viral load changes >0.5 log₁₀ are clinically significant when using the same laboratory and assay 2

Additional Specimen Types

For CMV disease diagnosis (not just viremia):

• CSF: Multiplex PCR assays available; any positive result is informative 2
• Bronchoalveolar lavage, tissue biopsies, vitreous/aqueous humor: Positive results are clinically meaningful 2
• Stool and BAL require normalization for interpretation 2

Resistance Testing

• Genotype by Sanger or next-generation sequencing when treatment fails 2
• Test all genes involved in antiviral mechanism of action 2

Serologic Testing

IgG and IgM antibodies can supplement PCR but are not primary diagnostic tools in acute settings 4, 5.

EBV Testing

Primary Methods Depend on Clinical Context

For transplant monitoring and acute infection: Use PCR on whole blood 3:

• Whole blood detects EBV DNA in 55% vs. plasma 18% - significantly more sensitive 3
• Correlation between whole blood and plasma is moderate (r=0.515), making whole blood clearly superior 3
• Detection rate in plasma varies by transplant type (higher in HSCT than liver transplant) 3

For acute infection diagnosis: Combine PCR with serology:

• EBV-specific antibody profiles: VCA-IgM, VCA-IgG, EA-IgG, EBNA-IgG
• In heterophile-negative patients with lymphocytosis, EBV IgM positivity occurs in 20-40% 5

Specimen Considerations

• Subgingival plaque shows 45% EBV detection vs. 37.5% in saliva and 25% in blood 6
• Low agreement between sampling methods for EBV (unlike CMV) - may need multiple sample types to avoid false negatives 6
• For CNS disease: CSF PCR with detection threshold of 5-15 genomes 7

Clinical Correlations and Pitfalls

Common Diagnostic Challenges

Toxoplasmosis:

• False-positive IgM is extremely common (20% of positive results) 1
• IgM can persist >1 year in chronic infection (40% of positive results) 1
• Always confirm positive IgM at reference laboratory before making treatment decisions

CMV:

• Some commercial assays deviate by ≥1.5 log IU/mL despite standardization 2
• CMV DNA may be undetectable in blood despite tissue disease (especially GI or retinitis) 2
• Kinetic analysis (doubling time <2 days) predicts need for preemptive therapy 2

EBV:

• Whole blood is far superior to plasma for detection 3
• Multiple positive viral serologies complicate diagnosis - 70% of patients with atypical lymphocytosis have positive serology for multiple pathogens 5
• Downey type II atypical lymphocytes specifically associate with EBV (p=0.006) 5

Co-infection Patterns

Patients with Toxoplasma IgG positivity show significantly higher rates of EBV-EA-IgG and EBV-VCA-IgA positivity 4. CMV IgM positivity is highest (60.5%) in EBV reactivation cases 4, suggesting potential diagnostic relevance of co-testing.

Pregnancy-Specific Considerations

CMV and Toxoplasma account for most confirmed maternal TORCH infections requiring specialist assessment 8. Transplacental infection incidence is approximately 1:200 for CMV 9, with 5-50% leading to miscarriage or preterm birth and 7-14% risk of sensorineural hearing loss even in asymptomatic neonates 9.