How do I obtain a diagnosis of Candida glabrata using a nucleic‑acid‑based assay (NAAT)?

Diagnosis of Candida glabrata Using Nucleic Acid Amplification Testing (NAAT)

To diagnose Candida glabrata using nucleic acid-based assays, obtain appropriate clinical specimens (blood, tissue, or vaginal swabs depending on infection site), transport them promptly to the laboratory, and request species-specific PCR or multiplex NAAT that includes C. glabrata detection—these molecular methods provide rapid (within hours to same-day), highly sensitive (>95%), and specific identification compared to culture alone. 1, 2

Specimen Collection and Transport

Blood Culture Specimens

• Obtain blood cultures if candidemia or disseminated infection is suspected, particularly in patients with systemic signs of infection, though conventional blood cultures detect only 50% of disseminated candidiasis. 3
• Blood culture bottles that signal positive for yeast should be processed immediately for NAAT testing, as results can be available within 3 hours using fluorescent in situ hybridization (FISH) methods or PCR-based assays. 4
• Transport blood culture bottles to the laboratory immediately upon positive signal to maximize detection sensitivity. 5

Tissue and Body Fluid Specimens

• Collect samples from normally sterile sites aseptically and transport to the laboratory promptly, as small samples are prone to sampling error. 5
• Keep samples moist and avoid placing them in histopathology fixatives if molecular testing is planned, as fixatives can interfere with nucleic acid extraction. 5
• If immediate processing is not possible, store specimens at 4–5°C (refrigeration temperature). 5

Vaginal Specimens (for Vulvovaginal Candidiasis)

• Use vaginal swabs placed in manufacturer-provided transport media for multiplex NAAT panels that detect C. glabrata alongside other Candida species. 5
• The FDA-cleared BD Max Vaginal Panel specifically detects C. albicans and resistant species (C. glabrata/krusei) and is approved for symptomatic females. 5
• Specimens remain stable at room temperature for up to 7 days in appropriate transport media. 5

Available NAAT Methods for C. glabrata

PCR-Based Assays

• Species-specific PCR targeting C. glabrata genomic sequences provides rapid detection with sensitivity of 10 CFU/µL and results within 30–60 minutes including sample preparation. 1
• Endpoint PCR methods using primers designed to amplify multiple species-specific genomic copies achieve highly specific detection without cross-reactivity with other Candida species or bacteria. 2
• Real-time PCR (qPCR) offers quantitative detection and is considered equivalent to culture methods for clinical sample identification. 1

Multiplex NAAT Panels

• Multiplex platforms simultaneously detect multiple Candida species including C. glabrata, which is critical because non-albicans species are increasingly common in diabetic and immunocompromised patients with different antifungal resistance patterns. 3
• The BD Max Vaginal Panel detects C. glabrata/krusei as a combined target, distinguishing these azole-resistant species from C. albicans. 5

Fluorescent In Situ Hybridization (FISH)

• PNA FISH provides dual-color identification of C. albicans (green) and C. glabrata (red) directly from positive blood culture bottles in less than 3 hours. 4
• This method demonstrates 100% sensitivity (37/37) and 100% specificity (82/82) for C. glabrata detection in multicenter validation. 4

NASBA (Nucleic Acid Sequence-Based Amplification)

• NASBA detects RNA from C. glabrata and other azole-resistant species with sensitivity of 1 colony-forming unit within one working day. 6
• This isothermal amplification method offers an alternative to PCR with comparable sensitivity and specificity. 6

Clinical Indications for NAAT Testing

High-Priority Scenarios

• Diabetic and immunocompromised patients with suspected fungal infection should always have NAAT testing given their higher risk of unusual pathogens and resistant organisms. 3
• All moderate-to-severe infections require molecular identification before initiating therapy to guide targeted antifungal selection. 3
• Patients with chronic wounds or recent antibiotic exposure require species-level identification to guide targeted therapy. 3

Species Identification Mandate

• Species-level identification is mandatory because C. glabrata displays relatively high MIC values to fluconazole and is associated with high mortality rates. 2
• Non-albicans species, particularly C. glabrata, have different antifungal resistance patterns that directly impact treatment selection. 3

Performance Characteristics

Sensitivity and Specificity

• PCR-based methods achieve >95% sensitivity and specificity for C. glabrata detection in clinical samples. 1, 2
• PNA FISH demonstrates 100% sensitivity and specificity when tested against reference strains and clinical isolates. 4
• NAAT methods detect C. glabrata without cross-reaction with other fungi or bacteria, including closely related Candida species. 1

Turnaround Time

• Rapid isothermal amplification methods (RPA-LFS) provide results within 20–30 minutes. 1
• PNA FISH from positive blood cultures yields results in less than 3 hours. 4
• Standard PCR protocols complete within 3–4 hours including sample preparation. 2

Critical Advantages Over Culture

• NAAT provides same-day or next-day results compared to 5–14 days required for some Candida species to grow in culture. 5
• Molecular methods maintain sensitivity even when patients have received antifungal therapy, whereas culture sensitivity decreases. 3
• Negative culture results do not exclude Candida infection, making NAAT particularly valuable in culture-negative cases. 5

Common Pitfalls to Avoid

• Do not rely on culture alone for C. glabrata identification, as delayed results (up to 14 days) can lead to inappropriate empiric therapy and increased mortality. 5, 2
• Avoid testing formed stool or asymptomatic patients, as this generates false-positive results and unnecessary treatment. 5
• Do not assume negative conventional blood cultures exclude disseminated candidiasis—consider NAAT on tissue or other sterile site specimens. 3
• Ensure specimens are not placed in histopathology fixatives if molecular testing is planned, as this destroys nucleic acids. 5