What lab test is used to diagnose Candida (Candida) auris infection?

Laboratory Testing for Candida auris Diagnosis

Blood cultures remain the primary diagnostic method for detecting Candida auris infection, followed by MALDI-TOF mass spectrometry or molecular sequencing for definitive species identification, as conventional biochemical methods frequently misidentify this organism. 1

Primary Diagnostic Approach

Blood Culture Collection

• Collect 2-3 blood culture sets with 20 mL blood volume per set when investigating potential candidemia, as diagnostic yield increases with blood volume and number of bottles 1
• Use automated validated blood culture systems, as these are strongly recommended over older methods 1
• Blood cultures have approximately 50% overall sensitivity for invasive candidiasis and median time to positivity of 2-3 days (range 1 to ≥7 days) 1

Species Identification (Critical Step)

Species-level identification is strongly recommended for all Candida isolates to guide treatment, detect outbreaks, and conduct surveillance 1

MALDI-TOF Mass Spectrometry (Preferred Method)

• MALDI-TOF MS is strongly recommended as the primary identification method for cultured isolates, provided the spectral database includes C. auris 1, 2
• This method overcomes the significant limitation that conventional biochemical platforms commonly misidentify C. auris as other Candida species (particularly C. haemulonii, C. duobushaemulonii, or C. famata) 3, 4, 5

Molecular Methods (When MALDI-TOF Unavailable or Confirmatory)

• DNA sequencing is strongly recommended, particularly in specialized laboratories or when MALDI-TOF cannot provide identification 1
• PCR targeting rDNA regions (ITS and D1/D2 regions of 28S ribosomal DNA) provides 100% concordance with sequencing results 3, 4
• Real-time PCR assays specific for C. auris are fast, robust, and easy to interpret, though ESCMID guidelines note these techniques lack full external validation and standardization 6, 3

Adjunctive Diagnostic Methods

Chromogenic Agar

• Chromogenic agars are strongly recommended for detecting mixed yeast infections and can provide presumptive identification 1
• Specialized CHROMagar formulations exist specifically for C. auris identification from laboratory specimens 2

Non-Culture Biomarker Tests

• β-D-glucan (BDG) testing (Fungitell™) is recommended for candidemia detection with sensitivity >65% and specificity >80% at cutoff 80 pg/mL 1
• Serial determinations twice weekly are recommended; particularly useful for ruling out infection (negative predictive value >85%) 1
• Mannan and anti-mannan antibody detection shows sensitivity/specificity around 80-85% and can be positive 6 days before blood cultures 1

Direct PCR from Blood

• PCR assays directly from blood are recommended with moderate strength, though they only detect some Candida species 1
• ESCMID guidelines note pooled sensitivity and specificity over 85% for in-house PCR techniques, but variability in methods remains a challenge 6

Antifungal Susceptibility Testing

EUCAST or CLSI antifungal susceptibility testing is strongly recommended for all C. auris isolates given the high rates of multidrug resistance 1

• Approximately 90% of C. auris isolates are resistant to fluconazole, 30% to amphotericin B, and 5% to echinocandins 4
• The CDC has defined tentative breakpoints for interpreting CLSI broth microdilution results specifically for C. auris 1

Critical Pitfalls to Avoid

• Never rely on conventional biochemical identification methods alone for C. auris, as misidentification is extremely common and can delay appropriate infection control measures 3, 4, 5
• Blood cultures may be negative in up to 50% of invasive candidiasis cases, particularly in deep-seated infections without candidemia 1
• False-positive BDG results occur with albumin, gauzes, immunoglobulins, or hemodialysis use 1
• Whole genome sequencing remains the gold standard for outbreak investigation and phylogenetic analysis, though not routinely available 7, 4