What does a Tetralogy of Fallot (TOF) or other condition abbreviated as THS follow-up entail in a 6-month-old infant?

THS Follow-Up in a 6-Month-Old: Transient Hypogammaglobulinemia of Infancy

THS follow-up in a 6-month-old refers to monitoring for Transient Hypogammaglobulinemia of Infancy (THI), a condition where infants have temporarily low immunoglobulin G (IgG) levels that typically normalize by early childhood. 1

What is Transient Hypogammaglobulinemia of Infancy (THI)?

• THI occurs when an infant's production of IgG antibodies is delayed after maternal antibodies (which normally protect for the first 3-6 months) have degraded 1
• It is characterized by repeatedly low immunoglobulin levels (primarily IgG, sometimes IgA and IgM) that are below the age-specific normal range 1
• 60% of affected patients are male 1
• Most infants with THI will spontaneously recover their IgG levels by early childhood (mean age of 27 months, with all patients reaching normal levels by 59 months in one study) 1

Clinical Manifestations

• Bacterial sinopulmonary infections and other respiratory tract infections are common 1
• Severe infections like sepsis or meningitis are rare in THI 1
• Some patients may be asymptomatic, while others may exhibit atopy or autoimmune diseases 1

Follow-Up Protocol for THI

• Regular monitoring of immunoglobulin levels (IgG, IgA, IgM) until normalization 1
• Assessment of specific antibody production and enumeration of lymphocyte subsets by flow cytometry 1
• Evaluation of responses to vaccines (most children have normal booster responses to protein vaccines) 1
• Monitoring for recurrent infections, particularly respiratory illnesses 1

Important Distinctions

• The definitive diagnosis of THI can only be made retrospectively after IgG levels have normalized 1
• Some children initially diagnosed with hypogammaglobulinemia of infancy may later develop Selective IgA Deficiency (SIGAD), Common Variable Immunodeficiency (CVID), or other forms of dysgammaglobulinemia instead of THI 1

Management Considerations

• Most cases require supportive care and monitoring rather than intervention 1
• For children with frequent infections, management may include prophylactic antibiotics or, in some cases, temporary IgG replacement therapy 1
• Careful monitoring is essential as some patients who initially appear to have THI may develop permanent immunodeficiencies 1

Prognosis

• Generally favorable with spontaneous resolution of immunoglobulin deficiency 1
• Most children achieve normal IgG levels by 5 years of age 1
• Close follow-up is important to distinguish true THI (which resolves) from more persistent immunodeficiencies 1