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A negative result does not rule out the diagnosis of IA. Repeat testing is recommended if the result is negative but IA is suspected. Patients at risk of IA should have a baseline serum tested and should be monitored twice a week for increasing galactomannan antigen levels.
Galactomannan antigen levels may be useful in the assessment of therapeutic response. Antigen levels decline in response to antimicrobial therapy.
False-positive results are reported to occur at rates of 8% to 14% with this assay. For all positive patients, it is recommended that a new aliquot of the same specimen be repeated, as well as collection of a new specimen from the patient for follow-up testing. Two or more consecutive positive results should be obtained from separately drawn specimens before the patient is considered to have a positive Aspergillus antigen test.
Numerous foods (pasta, rice, etc.) contain galactomannan. It is thought that damage to the gut wall by cytotoxic therapy, irradiation, or graft- versus-host disease enables translocation of the galactomannan from the gut lumen into the blood and may be partially responsible for the high false-positive rate of this assay.
Other genera of fungi such as Penicillium and Paecilomyces have shown reactivity with the rat EBA-2 monoclonal antibody used in the assay. These species are rarely implicated in invasive fungal disease. Cross reactivity with Alternaria species also has been reported.
Semisynthetic antibiotics such as piperacillin, amoxicillin, and augmentin, which are based on natural compounds derived from the genus Penicillium, have been demonstrated to cross-react with the rat EBA-2 monoclonal antibody used in the assay.
The specificity of the assay for Aspergillus species cannot exclude the involvement of other fungal pathogens with similar clinical presentations such as Fusarium, Alternaria, and Mucorales.
The performance of the assay has not been evaluated with neonate serum specimens or for use with plasma or other specimen types such as urine or cerebrospinal fluid.
The assay may exhibit reduced detection of galactomannan in patients with chronic granulomatous disease and Job's syndrome.
The concomitant use of antifungal therapy in some patients with invasive aspergillosis may result in reduced sensitivity of the assay.
False-positive galactomannan results are possible in patients receiving PLASMA-LYTE for intravenous hydration or if PLASMA-LYTE is used for bronchoalveolar lavage.
Specimens containing Histoplasma antigen may cross-react in the Aspergillus galactomannan assay.