Blood Tests for Candida Infections
Yes, there are several blood tests available for diagnosing Candida infections, including blood cultures, β-1,3-D-glucan (BDG) testing, and combined mannan antigen/anti-mannan antibody testing, though each has significant limitations and should be used as part of a comprehensive diagnostic strategy. 1
Blood Culture Testing
Blood cultures remain the standard diagnostic method for candidemia, but they have critical limitations:
- Sensitivity is only 50-75% when proper collection techniques are followed, meaning up to half of true infections may be missed 1
- Even lower sensitivity occurs in neutropenic patients and those already receiving antifungal treatment 1
- Requires 60 mL of blood for adults divided into three aerobic and three anaerobic bottles, obtained from different venipuncture sites 1
- Daily blood cultures are recommended when candidemia is suspected, with at least 5 days of incubation 1
- Species identification is mandatory because antifungal therapy varies by Candida species 1
Critical pitfall: Blood cultures can be negative in up to one-third of invasive candidiasis cases, particularly in ICU patients, so negative cultures do not exclude infection 1, 2
β-1,3-D-Glucan (BDG) Testing
The BDG test (specifically Fungitell®) is recommended for candidemia detection but is not Candida-specific:
- Sensitivity is 65-89% at the 80 pg/mL threshold, with specificity >80% 1, 3, 4
- Serial testing twice weekly is recommended rather than single measurements 1
- Negative predictive value is approximately 85%, meaning 15% false-negative rate 3
- Useful for ruling out infection when combined with clinical assessment 1
Major limitations and false positives occur with: 1, 4
- Albumin administration
- Gauze exposure
- Immunoglobulin infusions
- Hemodialysis
- Less reliable in hematological disease patients
Critical warning: A negative BDG result does not exclude candidemia and should never be used alone to withhold or discontinue antifungal therapy in critically ill patients with high clinical suspicion 3
Mannan Antigen and Anti-Mannan Antibody Testing
The combined Platelia Candida Antigen Plus and Antibody Plus tests are Candida-specific:
- Sensitivity approximately 80% and specificity 85% for candidemia 1
- Can detect infection 6 days earlier than blood cultures on average 1, 3
- Negative predictive value >85%, useful for ruling out infection 1
- Serial determinations may be necessary for optimal performance 1
- Recommended as part of diagnostic strategy to reduce unnecessary antifungal use in ICU settings 1
Clinical Decision Algorithm
For suspected invasive candidiasis, use this approach:
- Obtain blood cultures immediately using proper technique (60 mL from multiple sites) 1
- Order both BDG and mannan/anti-mannan testing for complementary information 1, 3
- Do not wait for test results before starting empiric echinocandin therapy if patient has septic shock with risk factors 3
- Repeat testing serially (BDG twice weekly, blood cultures daily) if initial results negative but suspicion remains high 1
- Only consider stopping therapy if ALL of the following are met: no clinical improvement, all cultures negative after 4-5 days, repeat BDG negative, no evidence of invasive disease, and alternative diagnosis confirmed 3
Tests NOT Recommended
PCR-based methods: Not validated for clinical use and no recommendations can be made 1
Antibody detection kits (Serion Elisa Classic, germ tube antibodies): Under evaluation with limited data 1
Stool cultures for Candida: Asymptomatic colonization should not be treated, and stool detection does not indicate invasive disease 2
Tissue Diagnosis (Gold Standard)
When accessible, tissue biopsy provides definitive diagnosis:
- Positive tissue culture with >10^5 organisms per gram or yeasts on microscopy is considered direct evidence of invasive infection 4
- Superior to biomarker testing as it provides species identification and guides targeted therapy 4
- Speciation and susceptibility testing should be routine for all isolates from sterile sites 4