Galactomannan and 1,3-β-d-glucan (1,3-BDG) are components of certain fungal cell walls. They have been studied as an aid in the diagnosis of invasive fungal disease (IFD), especially in hematologic malignancy and high risk surgical patients. The utility of these tests in other patient populations is less well known, but they may be commonly ordered. This can lead to both under and over diagnosis, and may increase cost without adding value.
Adult inpatients (n=130) from two campuses of a 781 tertiary care hospital who had a galactomannan and/or 1,3-BDG resulted between August 2014 to February 2015 were retrospectively evaluated. Our institution does not prospectively monitor levels; therefore only one sample per admission was analyzed. Variables reviewed included, but were not limited to, risk factors for IFD, results of imaging, the use of antifungal prophylaxis, fungal growth in any culture, use of piperacillin-tazobactam and detection of Pneumocystis jirovecii.
Most patients (n=67) had both assays performed. All 74 samples (serum) tested for galactomannan were negative (<0.5 pg/mL). Mold active antifungal prophylaxis was administered to 92% of persons status-post bone marrow transplantation who had a serum galactomannan assay performed. This markedly decreases the sensitivity of the test. 44% of patients received piperacillin tazobactam, consistent with data that this drug should rarely lead to a false positive result. Patients who did not have a hematologic malignancy accounted for 76% of serum galactomannan samples. There were 123 1,3-BDG samples sent, 18% were positive. 4% of 1,3-BDG test results prompted the administration of anti-fungal therapy in the absence of culture data. One patient with a positive test and a risk factor for Pneumocystis jiroveci infection was treated without visualization of the organism.
Serum galactomannan testing was uniformly negative as utilized in our patient population, perhaps as the patients at highest risk receive mold active antifungal prophylaxis. The results of 1,3-BDG testing rarely impacted therapy. Use of these tests in non-selected populations is rarely helpful. Prospective advice by infectious disease clinicians could assist in more judicious test ordering and has the potential to contribute to high value care.
E. Radigan, None
G. Scully, None