Rhodococcus induced false-positive galactomannan (GM), a biomarker of fungal presentation, in patients with peritoneal dialysis: case reports

Abstract

BackgroundGalactomannan index (GMI) at a level higher than 0.5 provides high sensitivity and specificity for the diagnosis of fungal peritonitis. Here, we report the false-positive of GMI in peritoneal dialysis (PD) effluent (PDE) due to Rhodococcus peritonitis in PD patients.Case presentationGMI in PDE of case #1 and case #2 were 1.53 and 0.76, respectively, while serum GMI of both cases was less than 0.5. In addition, GMI from the specimens obtained directly from the stationary phase of Rhodococcus colonies were 1.27 and 1.56, which were isolated from case #1 and #2, accordingly.ConclusionHigh GMI in PDE of PD patients is not specific just for fungal infections but may also be secondary to other infections, such as Rhodococcus spp., especially in endemic areas.

ISPD peritonitis guideline recommendations: 2022 update on prevention and treatment

“…156 For rapid diagnosis of fungal peritonitis, PD effluent and serum galactomannan index might offer a faster turnaround time than the conventional culture method, but with a diagnostic accuracy of 65.2% sensitivity, 85.0% specificity only. 157,158 False-positive galactomannan results 159 leading to unnecessary use of antifungals is a definite concern.…”

Serum Galactomannan: A Predictor of Poor Outcomes in Peritoneal Dialysis Patients With Fungal Peritonitis

“… 20 False positive GMI has also been reported in rhodococcal peritonitis. 21 Some generic formulations of piperacillin/tazobactam, colistin inhalation, and massive hemolysis may also result in false positive serum GMI values. 22 , 23 , 24 , 25 Yeasts have minimal GM in their cell walls, such that serum GMI has limitations for detection of yeast infection.…”

A case of Neurospora sitophila causing PD peritonitis

“…Peritoneal 6,7 and serum 8,9 BDG appears to have greater sensitivity and specificity than galactomannan in fungal infections and can potentially be used alone as a predictive marker of fungal peritonitis, whereas galactomannan alone can lead to false positive results. 10 The utility of a positive serum BDG (above 80 pg/mL as per manufacturer guidelines) may therefore lie in guiding earlier initiation of therapeutic antifungal treatment pending definitive identification of an organism.…”