What is the role of lab testing in the workup of mucormycosis (zygomycosis)?

Updated: Jul 06, 2021
  • Author: Avnish Sandhu, DO; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
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A complete blood cell (CBC) count should be obtained to assess for neutropenia. A chemistry panel that includes blood glucose, bicarbonate, and electrolytes is useful to monitor homeostasis and correction of acidosis. An arterial blood gas (ABG) study can help determine the degree of acidosis and guide corrective therapy. Iron studies may be indicated to assess the presence of iron overload as shown by high ferritin levels and a low total iron-binding capacity. In cases of central nervous system (CNS) involvement, cerebrospinal fluid (CSF) findings may include elevated protein levels and a modest mononuclear pleocytosis. CSF fungal stain and cultures are typically sterile. A CT scan should precede a lumbar puncture to assess for evidence of space occupying lesions, which could lead to herniation.

Blood cultures can be obtained; however, they are usually negative despite the angioinvasive nature of the organism. Blood cultures may be useful to detect bacteremia in addition to Mucorales infection. One study of pulmonary mucormycosis identified concurrent bacteremia as an independent predictor of 28-day mortality. [59] There are no specific biomarkers to identify mucormycosis. Bronchoalveolar lavage (BAL) of fluid culture has a low yield, with a sensitivity of 20%-50%. Antigen tests (beta-D-glucan or galactomannan) are not useful for detecting this infection. [28] ECMM guidelines strongly recommend obtaining a culture of the specimen to identify the organism. [39] Cultures should be incubated at 30°C and 37°C; direct microscopy should be done mainly to identify septation, branching angle, and hyphal width. [39] ECMM guidelines strongly recommend susceptibility testing to expand epidemiological knowledge, although generally use of standard method for susceptibility testing for Mucorales is marginally reinforced as there are no cut-off values established by European Committee on Antimicrobial Susceptibility testing (EUCAST) or Clinical and Laboratory Standards Institute (CLSI). [39]

Molecular based testing is moderately supported; fresh tissue is preferred over paraffin tissue, as formalin damages DNA. [39]  The use of molecular based testing has only moderate support due to lack of standardization. The use of quantitative polymerase chain reaction (qPCR) for detection of circulating DNA from common Mucorales species (Lichtheimia species, Rhizomucor species, and Mucor/Rhizopus species), while not yet commercially available, has been described and appears promising for the early diagnosis of mucormycosis in high-risk patients. [65, 66] In a retrospective analysis of 44 cases, qPCR identification was fully concordant with that of culture. Assay positivity was observed at an average of 9 days, at least 2 days prior to positive imaging findings. Development of PCR negativity after treatment was associated with higher survival rates (48% vs 4%), suggesting that this modality could eventually be used for treatment monitoring. [67] DNA detection can be looked for in CSF or BAL clinical samples. [68, 69, 70, 71]

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