What is the appropriate evaluation and workup for a patient with recurrent infections?

Workup for Recurrent Infections

For a patient with recurrent infections, begin by determining whether infections are primarily sinopulmonary (suggesting antibody deficiency) versus skin/soft tissue (suggesting phagocytic defects) versus unusual organisms (suggesting combined immunodeficiency), as this pattern directs the initial laboratory evaluation. 1

Initial Clinical Assessment

Infection Pattern Recognition

• Recurrent sinopulmonary infections (sinusitis, otitis media, pneumonia) occurring ≥2 times per year suggest antibody-mediated immunodeficiency and warrant immunoglobulin testing 1
• Recurrent skin and soft tissue infections with Staphylococcus aureus point toward phagocytic cell defects or STAT3 deficiency 1
• Severe infections with unusual pathogens (fungi, mycobacteria, viruses) indicate combined immunodeficiency or innate immune defects 1
• Recurrent throat infections meeting criteria of <7 episodes in past year, <5 episodes per year over 2 years, or <3 episodes per year over 3 years should prompt watchful waiting rather than immediate immunologic workup 1

Critical Historical Elements

• Medication history is essential, as phenytoin, carbamazepamine, valproic acid, sulfasalazine, gold, penicillamine, hydroxychloroquine, and NSAIDs can cause acquired IgA deficiency or hypogammaglobulinemia 1
• Family history of early deaths, recurrent infections, or consanguinity suggests hereditary immunodeficiency 1
• Age of onset: infections beginning in infancy suggest severe combined immunodeficiency or phagocytic defects, while onset after age 2-4 years suggests antibody deficiency 1

Laboratory Evaluation Algorithm

First-Tier Testing for Antibody Deficiency

When sinopulmonary infections predominate:

• Quantitative immunoglobulins (IgG, IgA, IgM) with age-matched reference ranges 1
• Specific antibody responses to protein antigens (tetanus, diphtheria) and polysaccharide antigens (pneumococcal serotypes) before and 4 weeks after vaccination 1
• Complete blood count with differential to assess lymphocyte and neutrophil counts 1

IgG subclass measurement should NOT be routinely ordered as initial testing, since approximately 2.5% of healthy individuals will have low levels by statistical definition, and results rarely change management when total immunoglobulins and specific antibodies are normal 1

Interpretation of Antibody Testing

• Selective IgA deficiency is diagnosed when IgA <7 mg/dL with normal IgG and IgM 1
• IgG subclass deficiency requires confirmation with repeat measurement at least 1 month apart, plus demonstration of impaired vaccine responses 1
• Specific antibody deficiency is defined by failure to mount protective antibody responses (typically <1.3 mcg/mL) to ≥50% of pneumococcal serotypes despite normal immunoglobulin levels 1

Second-Tier Testing Based on Initial Results

If antibody testing is normal but clinical suspicion remains high:

• Lymphocyte subset analysis (CD3, CD4, CD8, CD19, CD16/56) to evaluate T-cell, B-cell, and NK-cell populations 1
• Complement levels (CH50, C3, C4) if recurrent Neisseria infections or autoimmune features present 1

For recurrent skin/soft tissue infections:

• Neutrophil oxidative burst assay (dihydrorhodamine test) to screen for chronic granulomatous disease 1
• Immunoglobulin E level if eczema, elevated eosinophils, or staphylococcal abscesses suggest hyper-IgE syndrome 1

Management Based on Findings

For Confirmed Antibody Deficiency

• Immunoglobulin replacement therapy (IVIG or subcutaneous IG) at 400-600 mg/kg every 3-4 weeks for patients with hypogammaglobulinemia and recurrent infections 1
• Aggressive antimicrobial therapy and prophylaxis for patients with selective IgA deficiency who have frequent infections despite normal IgG 1
• Avoid IgA-containing blood products in IgA-deficient patients with anti-IgA antibodies to prevent anaphylaxis 1

For Recurrent MRSA Skin Infections

When hygiene measures fail:

• Decolonization regimen: mupirocin nasal ointment twice daily for 5-10 days PLUS chlorhexidine body washes for 5-14 days or dilute bleach baths (¼ cup per ¼ tub) twice weekly for 3 months 1
• Household contact screening and treatment if interpersonal transmission suspected 1
• Long-term antibiotic prophylaxis only after decolonization attempts fail 1

For Normal Immunologic Workup

If comprehensive testing is normal:

• Consider autoinflammatory syndromes if recurrent fevers with rash, arthritis, or serositis present 1
• Evaluate for anatomic abnormalities: sinus CT for chronic sinusitis, chest CT for bronchiectasis, urologic imaging for recurrent UTIs 1
• Reassess for secondary causes: uncontrolled diabetes, malnutrition, occult malignancy, or medication effects 1

Common Pitfalls to Avoid

• Do not order IgG subclasses as first-line testing—they add cost without changing management when total immunoglobulins are normal 1
• Do not diagnose IgG4 deficiency before age 10 years—normal ranges are poorly defined in young children 1
• Do not use metronidazole for recurrent C. difficile infections—it has lower sustained response rates and potential neurotoxicity with prolonged use 1
• Do not treat asymptomatic bacteriuria in elderly patients—this fosters antibiotic resistance without clinical benefit 2
• Do not assume immunodeficiency in patients taking immunosuppressive medications—this represents secondary rather than primary immunodeficiency 1