Monday, 1 July 2013

False Positive Galactomannan Test after Ice-Pop Ingestion

An unusual case history has recently been presented in the New England Journal for Medicine. A patient was given a stem cell transplant and as is normal was then monitored closely for infection as vulnerability to infection is high at this point. Monitoring for fungal infection is routinely carried out using a direct assay to detect fungal cell wall components (galactomannan) in the patients blood - if found it would suggest that the patient had a fungal infection somewhere in their body that was releasing tiny particles of cell wall into their blood.
Over the next 4 weeks signs of fungal infection were not present (see fig 1 above), however during week 5 the test started to pick up signs of apparent infection - see days 32, 34 and 36 above. The galactomannan test is very reliable and no causes of false positive results where found so treatment was begun for fungal infection using an antifungal drug.

The patient had no other signs of infection despite extensive testing (CT scans, sputum, PCR), raising suspisions that something was wrong with this diagnosis. The only food item being consumed by the patients at this time were frozen fruit flavoured water in the form of ice-pops. On testing it was found that these drinks  contained significant amounts of fungal growth (Penicillin) and as the amounts detected declined soon after it was assumed that this was the source of a false positive galactomannan test result and the drinks were stopped.

The authors caution fellow doctors that other foodstuffs could potentially cause false positives as they also contain types of galactomannans. These can include the types of food given to similar patients as cooling drinks, ice cream etc.

In this case unnecessary antifungal medication was administered which can complicate treatment and cause severe side effects so it would have been better to avoid giving it.

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