What is the interpretation and management of a positive TORCH (Toxoplasmosis, Other, Rubella, Cytomegalovirus, Herpes) panel report?

Interpretation and Management of a Positive TORCH Panel Report

A positive TORCH panel requires targeted follow-up testing at reference laboratories to confirm the specific infection, determine if it is acute or chronic, and guide appropriate management based on patient population (pregnant women, neonates, or immunocompromised individuals). 1

Understanding TORCH Panel Components

TORCH is an acronym representing:

• Toxoplasmosis (caused by Toxoplasma gondii)
• Other infections (including syphilis)
• Rubella virus
• Cytomegalovirus (CMV)
• Herpes simplex virus (HSV) 2, 3

Interpretation Principles

General Approach

• Positive results from non-reference laboratories should be confirmed at specialized reference laboratories before making definitive diagnoses 1
• Approximately 60% of positive Toxoplasma IgM results from non-reference laboratories do not represent recent infections when tested at reference laboratories 1
• Single serum testing (typical of TORCH screens) is often inadequate for definitive diagnosis 3

Specific Interpretation by Pathogen

Toxoplasmosis

• Positive IgG with negative IgM: Past infection, typically not clinically significant 1
• Positive IgG and IgM: Requires confirmation at reference laboratory and additional testing including IgG avidity to determine if infection is recent 1
• Congenital toxoplasmosis can occur through: maternal primary infection during pregnancy, reactivation in immunocompromised pregnant women, or reinfection with more virulent strain 1

CMV

• Positive CMV IgG alone: Indicates past exposure and immunity, not active infection 4
• Positive IgG and IgM: Requires IgG avidity testing to determine timing of infection 4
• In immunocompromised patients, viral load testing is more relevant than antibody testing 4

Rubella, HSV and Other Pathogens

• Interpretation follows similar principles of distinguishing between past exposure (IgG only) and recent/active infection (IgG + IgM) 3
• Clinical context is crucial for interpretation 2

Management Based on Patient Population

Pregnant Women

1. For positive Toxoplasma results:

   • Confirm at reference laboratory (e.g., Palo Alto Medical Foundation-Toxoplasma Serology Laboratory) 1
   • If acute infection confirmed, consider amniocentesis for Toxoplasma PCR after 18 weeks gestation 1
   • Initiate appropriate antimicrobial therapy if acute infection confirmed 1

2. For positive CMV results:

   • In pregnant women, positive CMV IgG alone indicates immunity and low risk of congenital CMV 4
   • If both IgG and IgM positive, perform IgG avidity testing 4
   • Consider amniocentesis for CMV PCR if acute primary infection suspected 5

3. For other TORCH pathogens:

   • Management depends on specific pathogen and timing of infection 2

Neonates

1. For suspected congenital toxoplasmosis:

   • Test infant serum for Toxoplasma IgG, IgM (ISAGA), and IgA 1
   • Perform PCR on peripheral blood, urine, and CSF 1
   • Complete clinical evaluation including detailed physical examination, neurologic evaluation, ophthalmologic examination, and brain imaging 1

2. For suspected congenital CMV:

   • Viral culture or PCR of urine or saliva within 2-3 weeks of birth 4
   • Complete evaluation including hearing assessment, ophthalmologic examination, and neuroimaging 4
   • Consider valganciclovir treatment for symptomatic congenital CMV 6

Clinical Relevance and Limitations

• The diagnostic yield of TORCH serology for non-specific ultrasound abnormalities is low 5
• In cases of fetal growth restriction, complete TORCH screening appears unnecessary; CMV testing may be considered but has low yield (1.8%) 7
• Recent systematic reviews suggest retiring the TORCH acronym and avoiding reflex ordering of TORCH panels 5

Common Pitfalls to Avoid

• Misinterpreting positive IgG as evidence of active infection 4
• Failing to confirm positive results from non-reference laboratories 1
• Relying solely on serology for diagnosis in immunocompromised patients 4
• Ordering TORCH panels for non-specific findings without clinical suspicion 5
• Not considering timing of infection in relation to pregnancy when assessing risk to fetus 1

Prevention Strategies

• Primary prevention of maternal infections during pregnancy is the cornerstone of preventing congenital infections 2
• Preconception counseling should include prevention of TORCH infections 1
• Routine screening for TORCH infections is not recommended in all pregnant women but may be considered in high-risk situations 1