Surrogate Marker Offers Diagnosis of Fungal Disease

A fungal surrogate marker, (1-3)-β-D glucan, offers a noninvasive method for the potential surveillance and diagnosis of invasive fungal infections. Testing for (1-3)-β-D-glucan requires a minimally invasive sample that can be used to aid in the diagnosis of an invasive fungal infection as well as monitor the response to treatment.

Kits intended for the in vitro diagnosis of an invasive fungal infection contains lyophilized horseshoe crab coagulation factor (factor G) and the chromogenic substrate p-nitroanilide (Boc-Leu-Gly-Arg-p-nitroanilide). Typically, 3-5 mL of blood is collected into a serum separator tube (SST) with the minimum amount of serum volume recommended being 0.5 mL for adults and 0.2 mL for pediatric patients.

Following pretreatment of the sample with an alkaline solution, the reconstituted coagulation factor and chromogenic substrate are combined with the clinical serum sample and then incubated. Cleavage of p-nitroanilide from the chromogenic peptide produces the yellow color that is then measured spectrophotometrically. Blood samples that are lipemic, icteric, or hemolyzed should not be tested due to the inaccurate spectrophotometric values that can occur with these samples.

A prospective trial evaluating the usefulness of measuring serum (1-3)-β-D-glucan concentrations using a single serum sample and a determined cut-off value of >60 pg/mL as a screening test for the early diagnosis of an invasive fungal infection. This test showed a sensitivity and specificity of 88.9% and 19.8%, respectively. A trial in the USA used the recommended 80 pg/mL positive cut-off value in serum samples from eight different patient groups for the diagnosis of an invasive fungal infection. The trial established the 60-79 pg/mL as the indeterminate range for result reporting, with the negative range for the assay being below 60 pg/mL. One disadvantage of (1-3)-β-D-glucan testing is that a positive test alone lacks sufficient sensitivity and specificity for a definitive diagnosis.

The advent, approval, and use of the serum (1-3)-β-D-glucan assay have changed the testing practices for patients at risk of developing or patients with invasive fungal infections. The Fungitell Assay Kit (Associates of Cape Cod, Inc.; East Falmouth, MA, USA) is intended to be used for the detection of serum (1-3)-β-D-glucan as an aid in the diagnosis of invasive mycoses. It has the US Food and Drug Administration (FDA; Silver Springs, MD, USA) approval. A review of the subject was published on November 14, 2011, in the journal Laboratory Medicine.

Related Links:
Associates of Cape Cod, Inc.
US Food and Drug Administration