Assay Sheet

For in vitro diagnostic use

Test ID Code

CPT Code

Clinical Utility

• Candida spp.                       
• Acremonium
• Aspergillus spp.                 
• Coccidioides immitis
• Fusarium spp.                      
• Histoplasma capsulatum
• Trichosporon spp.              
• Sporothrix schenckii
• Saccharomyces cerevisiae
• Pneumocystis jiroveci

Procedure

Specimens

Collect 3 to 5 ml blood specimen in a gel separator tube (SST) without anti-coagulants. Allow specimen to clot, then centrifuge specimen within 2 hours of draw to pellet cells below the gel. Minimum volume of 0.5 mL serum for adults and 0.2 mL for infant (see assay limitations) and pediatric samples following centrifugation. Specimen should be stored at 2 to 8°C or frozen in non-self defrosting freezer and shipped with frozen gel packs or dry ice for overnight delivery at ViraCor. The serum can be decanted into a suitable container that is free of interfering levels of (1,3)- β-D-glucan.

Causes for Rejection

• Lipemic, icteric, or hemolyzed specimens.
• Specimens that have been stored at ambient temperature.
• Specimens that have been stored at 2 to 8°C for >5 days.
• If storage longer than 5 days is needed, samples should be frozen at -20°C or colder. Unless indicated as stored frozen, the specimen will be rejected if the draw date is >5 days from receipt at ViraCor.

Assay Limitations

• There are reports in the peer reviewed literature of lowered assay specificity in patients with gram positive bacteremia.
• Patients with renal failure on hemodialysis utilizing cellulose membranes may have false positive results.
• Patients treated with fractionated blood products such as albumin and immunoglobulin and in specimens and subjects exposed to glucancontaining gauze. Patients require 3 to 4 days for the restoration of baseline levels of serum (1,3)- β-D-glucan, after surgical exposure to (1,3)- β-D-glucan-containing sponges and gauze. Accordingly, the timing of sampling of surgical patients should take this into account.
• Samples obtained by heel or finger stick methods are unacceptable as the alcohol-soaked gauze used to prepare the site (and potentially, the skin surface-pooling of blood) has been shown to contaminate the specimens.
• A negative test result cannot rule out the diagnosis of invasive fungal disease. Patients at risk for invasive fungal disease should be tested twice per week.
• The performance of the Fungitell β-D Glucan assay has not been evaluated with specimens from neonates and infants <6 months of age.
• Patients whose GI tract is colonized with Candida and have mucositis may have a positive Fungitell β-D Glucan assay result without invasive fungal disease.

Reference Values

• Negative: Less than 60 pg/ml
• Indeterminate: 60 to less than 80 pg/ml
• Positive: Greater than or equal to 80 pg/ml

Turnaround Time

Shipping

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Pathogen Overview

Organism

Candida is the most common cause of opportunistic mycoses worldwide.  It is a yeast that is part of the normal flora of the skin, mouth, and other mucosal surfaces.  Additionally, it is found in the environment, particularly on leaves, flowers, water, and soil.  The genus Candida includes nearly 160 species. Among these, six are most frequently isolated in human infections. Candida albicans is the most abundant and significant species, but Candida tropicalis, Candida glabrata, Candida parapsilosis, Candida krusei, and Candida lusitaniae are also isolated as causative agents of Candida infections. Additionally, there has been a recent increase in infections due to non-albicans Candida spp., such as Candida glabrata and Candida krusei.

Clinical Manifestations 

Invasive Candidiasis (IC) is not a disease seen in normal healthy hosts.  However, Candida spp. can act as opportunistic pathogens in populations with compromised immune systems, leading to invasive disease.  The risk is pronounced in the early phase of neutropenia after intensive chemotherapy for acute myeloid leukemia (AML) or bone-marrow transplant.  The incidence in this group has been reported in 15 to 20% of allograft and autograft recipients.¹  Additional risk factors for IC include underlying haematological malignancy, neutropenia, graft-versus-host-disease (GVHD), conditioning agents, solid organ transplant, and central venous catheterization.   Unfortunately, the clinical manifestations of IC are often nonspecific.  Fever is often the only clinical clue of IC in high-risk patients. Likewise, progressive sepsis with multi-organ failure has been described in surgical patients who are developing IC. Thus, persistent, unexplained fever or sepsis that is not responding to broad-spectrum antibiotics is the setting for more acute forms of the disease.  Additionally, macronodular skin rash and retinal lesions are characteristic of invasive disease.  Candida is the most commonly recovered fungus in opportunistic mycoses.  Although the incidence of IC has stabilized at 10 to 20%, mortality remains high among high-risk patients with a rate of 40 to 50%.²

Diagnosis

An early, accurate diagnosis of IC has become essential in light of growing evidence that timely diagnosis is associated with improved patient survival.  Additionally, tests with high positive and negative predictive values may allow physicians to more precisely tailor treatment plans, as to avoid indiscriminate use of expensive and potentially toxic antifungal drugs.  An enormous challenge in the diagnosis of IC is the inadequate sensitivity of current “gold standard” diagnostic methods.  Blood cultures demonstrate sensitivity under 50%.² Therefore, diagnosis is based on a combination of clinical symptoms, radiological findings, histopathology, culture, and molecular assays.  Specifically, recent studies have indicated the value of molecular assays that detect fungal cell-wall components such as (1,3)β-D-glucans.^2-6  When utilized to monitor IC, sensitivity and specificity have been assessed at over 90%.²  Moreover, antigenemia declines during therapy, indicating the utility of (1,3)β-D-glucan testing to monitor the effectiveness of antifungal treatment.³

Treatment

Utilizing the proper diagnostic tools, clinicians have developed protocols to effectively treat IC.  Due to the possibility of rapidly progressing IC infection, prophylactic treatment has become the standard of care for high-risk populations.  There are a number of antifungal drugs that are available to treat IC. Fluconazole is a drug that can be taken by mouth or given intravenously to treat IC. Another class of antifungal drugs, the echinocandins, is also commonly utilized. All antifungals can cause serious problems, including kidney and liver damage, and may interact with other medications given to patients with weakened immune systems.  Therefore, using the proper tools to accurately diagnose and monitor the course of IC is essential to increase the likelihood of positive outcomes.   

References