Paper I
Question
Laboratory diagnosis of invasive candidiasis.
Answer
Laboratory diagnosis of invasive candidiasis:
- Blood culture — the traditional gold standard for candidaemia, but sensitivity is limited (~50–70%) and turnaround time slow (often 2–5 days); using dedicated fungal blood culture bottles/systems improves yield.
- Culture from other sterile-site specimens (CSF, peritoneal fluid, tissue biopsy) — depending on the site of suspected invasive disease.
- (1,3)-beta-D-glucan assay — a fungal cell-wall component detectable in serum; useful as an adjunctive marker for invasive fungal infection (including candidiasis), though not specific to Candida (also positive in other invasive fungal infections).
- PCR-based molecular assays — increasingly used for rapid detection directly from blood, offering faster turnaround than culture.
- Species identification — germ tube test (presumptive C. albicans), CHROMagar, biochemical/automated systems — important given rising incidence of intrinsically more resistant non-albicans species (C. glabrata, C. krusei, C. auris).
- Antifungal susceptibility testing — essential given variable resistance patterns, particularly relevant for the emerging multidrug-resistant C. auris.
- Histopathology (PAS/GMS stain) — of biopsy material, demonstrating tissue invasion, confirming invasive disease versus mere colonization.
- Ophthalmological examination — fundoscopy to look for candidal endophthalmitis/chorioretinitis in candidaemic patients, an important complication screen.