What are the recommended markers for diagnosing fungal infections?

Diagnostic Markers for Fungal Infections

For invasive fungal infections, use serum galactomannan testing for suspected aspergillosis in immunocompromised patients, β-D-glucan for invasive candidiasis in critically ill patients, and combined mannan antigen/anti-mannan antibodies for invasive candidiasis, with BAL galactomannan when serum testing is negative but clinical suspicion remains high. 1

Aspergillosis Diagnostic Markers

Serum Galactomannan Testing

• Perform serum galactomannan testing twice weekly or more frequently in severely immunocompromised patients (neutropenia, hematological malignancy, stem cell or solid organ transplant recipients) with unexplained lung infiltrates 1
• Sensitivity is 71% (95% CI 0.64-0.78) and specificity is 89% (95% CI 0.84-0.92) using an optical density index cutoff of 1.0 2
• Test at least twice weekly during granulocytopenia (<500 cells/μL) 1

BAL Galactomannan Testing

• Perform BAL galactomannan in patients with negative serum galactomannan but strong risk factors for invasive aspergillosis, or positive serum galactomannan with confounding factors (chemotherapy, mucositis) 1
• BAL galactomannan demonstrates superior performance: sensitivity 84% (95% CI 0.73-0.91) and specificity 88% (95% CI 0.81-0.91) 2
• BAL testing has sensitivity of 74% and specificity of 85% at cutoff of 0.5 3

Aspergillus PCR Testing

• Blood or serum Aspergillus PCR has sensitivity of 81% (95% CI 0.73-0.86) and specificity of 79% (95% CI 0.68-0.86) 2
• BAL PCR demonstrates higher accuracy: sensitivity 90% (95% CI 0.77-0.96) and specificity 96% (95% CI 0.93-0.98) 2
• Use PCR in combination with galactomannan testing, not as standalone diagnostic tool 1
• PCR is not yet standardized or widely available, therefore not mandatory in current recommendations 1

Invasive Candidiasis Diagnostic Markers

β-D-Glucan (BDG) Testing

• Screen high-risk hematological patients with serum β-D-glucan testing for invasive fungal infections 1
• In ICU patients at risk for invasive candidiasis: sensitivity 81% (95% CI 0.74-0.86), specificity 60% (95% CI 0.49-0.71) 2
• In hematological malignancy patients: sensitivity 50-70%, specificity 91-99% 3
• Do not rely on β-D-glucan as sole diagnostic test due to limited specificity 1, 3
• False-positives occur with early ICU admission, concurrent bacterial infections, and certain medical interventions 3

Mannan Antigen and Anti-Mannan Antibodies

• Use combined mannan antigen (Mn) and anti-mannan antibodies (A-Mn) testing via ELISA for invasive candidiasis diagnosis 1
• Mannan antigen alone: sensitivity 58% (95% CI 53-62), specificity 93% (95% CI 91-94) 1
• Anti-mannan antibodies alone: sensitivity 59% (95% CI 54-65), specificity 83% (95% CI 79-97) 1
• Combined Mn/A-Mn testing achieves optimal performance: sensitivity 83% (95% CI 79-87), specificity 86% (95% CI 82-90) 1
• Combined testing detects infection 6-7 days before blood culture positivity in 73% of candidemia cases 1
• In hepatosplenic candidiasis, 86% of patients had positive Mn or A-Mn results 16 days before radiological detection 1

Candida Antibody and Antigen Testing

• Routine Candida antibody and antigen testing is NOT recommended for patients with hematological malignancies 1

Endemic Mycoses Diagnostic Markers

Blastomycosis

• Use serum antibody testing specifically directed against anti-BAD-1 (anti-Blastomyces adhesin 1) antigen in combination with other non-cultural tests 1

General Endemic Mycoses (Histoplasmosis, Coccidioidomycosis, Blastomycosis)

• Perform serum antibody testing specific to the suspected pathogen 1, 3
• Use urine antigen testing when available 3
• Data on diagnostic accuracy varies according to test type, patient immunity status, and specific endemic disease 2

Diagnostic Algorithm for High-Risk Patients

Before Granulocytopenia

• Baseline screening: abdominal ultrasound and chest X-ray 1
• Serological tests and PCR are optional 1

During Granulocytopenia (<500 cells/μL)

• Perform Aspergillus galactomannan antigen testing and/or PCR at least twice weekly 1
• Daily physical examination 1

Persistent Fever (48-72 hours despite antibiotics)

• Obtain blood cultures before initiating antifungal therapy 1
• Weekly abdominal ultrasound 1
• Weekly chest X-ray or CT if clinically indicated 1
• Bronchoscopy with BAL for pulmonary signs and symptoms 1
• Repeat all procedures if fever persists beyond 1 week 1

Critical Caveats and Pitfalls

False-Positive Results

• Galactomannan false-positives occur in patients receiving chemotherapy or with mucositis due to cross-reactive epitopes from other fungi or bacteria penetrating intestinal mucosa 1
• β-D-glucan false-positives occur with bacterial infections and certain medical interventions 3

Tissue Processing

• Avoid homogenization (grinding or bead-beating) of tissue samples when filamentous fungal infections are suspected 4
• Homogenization significantly reduces organism recovery rates and fungal element detection on direct microscopy 4
• Dice tissue into small portions instead of homogenizing to preserve fungal hyphae 4

Specimen Handling

• Process BAL samples within 4 hours of collection 3
• Dilute biopsy specimens for PCR testing in isotonic saline, not formalin, to preserve DNA integrity 3

Combined Testing Strategy

• Use multiple diagnostic methods simultaneously rather than relying on single tests 1, 5
• No single test has sufficient sensitivity to rule out fungal infection 3, 5
• Combination of culture, direct microscopy, antigen detection, and molecular methods provides optimal diagnostic yield 1, 3, 5