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Published on: January 8, 2014
Significant decline in Galactomannan Signal during storage of clinical serum samples
Gemma L Johnson1, Shah-Jalal Sarker, Kate Hill
1Blizard Institute of Cell and Molecular Science, Queen Mary University of London, London E1 2AT, UK. s.g.agrawal@qmul.ac.uk.
Abstract:
Galactomannan (GM) is widely used for detection of invasive aspergillosis in high-risk haemato-oncology patients. Recent publications have reported a lack of repeatability of GM detection. The objective of this retrospective study was to assess the repeatability of GM levels during storage of clinical samples. In a GM screening strategy, positive sera were repeat tested as per manufacturer's recommendations. Short-term (ST) storage of samples was at +4 °C while long-term (LT) storage was at -80 °C. Bronchoalveolar (BAL) fluid was also repeating tested after ST storage and LT storage. Wilcoxon Signed Ranks Test was employed to assess the repeatability of GM levels. In a subset of 14 GM positive sera, repeat testing was performed on both the original serum and ethylenediaminetetraacetic acid (EDTA) pre-treated sample. There was a significant reduction in GM signals on repeat testing following ST storage (median GM index: 0.65 vs. 0.19; p < 0.001) and LT storage (median GM index: 0.56 vs. 0.10; p < 0.001) of serum samples. Of samples that were initially GM positive, an average GM index reduction of 50% was seen, with approximately two-thirds becoming GM negative on repeat testing of the same sample. In contrast, GM signal loss was not seen on repeat testing of BAL fluid following ST or LT storage. When GM positive serum samples were repeat tested using EDTA pre-treated serum from the first step of the testing protocol, all samples remained GM positive. In contrast, when the same samples were repeat tested from the original collected serum, 9 samples (64%) became GM negative. The significant reduction in GM signals during ST and LT storage of serum samples has implications for clinical management. Although the reasons for GM decline are unknown, they occur prior to the EDTA pre-treatment stage, indicating that the time from phlebotomy to testing should be minimized. BAL fluid GM index values remain stable.
Insights
Galactomannan (GM) levels in serum decrease significantly during storage, potentially leading to false negatives in invasive aspergillosis diagnosis. Bronchoalveolar lavage fluid GM levels remain stable.
Area of Science:
- Medical diagnostics
- Mycology
- Clinical chemistry
Background:
- Galactomannan (GM) is a biomarker for invasive aspergillosis in immunocompromised patients.
- Recent studies indicate variability in GM detection, questioning its diagnostic reliability.
- Standardized testing protocols are crucial for accurate interpretation of GM results.
Purpose of the Study:
- To evaluate the repeatability of galactomannan (GM) detection in clinical samples after short-term (ST) and long-term (LT) storage.
- To assess the impact of storage conditions on GM levels in serum and bronchoalveolar lavage (BAL) fluid.
- To investigate the influence of ethylenediaminetetraacetic acid (EDTA) pre-treatment on GM stability.
Main Methods:
- Retrospective analysis of GM levels in stored serum and BAL fluid samples.
- Repeat testing of GM-positive samples after ST (+4 °C) and LT (-80 °C) storage.
- Comparison of GM results from original serum versus EDTA-pre-treated samples.
- Statistical analysis using the Wilcoxon Signed Ranks Test.
Main Results:
- Significant reduction in GM index observed in repeat testing of serum samples after both ST (median 0.65 vs. 0.19) and LT (median 0.56 vs. 0.10) storage.
- Approximately two-thirds of initially GM-positive serum samples became GM-negative upon repeat testing after storage.
- No significant GM signal loss was detected in BAL fluid samples after ST or LT storage.
- EDTA pre-treatment of serum samples prevented GM index reduction, while original serum samples showed a decrease in 64% of cases.
Conclusions:
- Serum galactomannan (GM) levels decline significantly during storage, impacting the accuracy of invasive aspergillosis diagnosis.
- The observed GM decline occurs before EDTA pre-treatment, highlighting the importance of minimizing the time between sample collection and testing.
- Bronchoalveolar lavage fluid (BALF) GM levels demonstrate stability during storage, suggesting it as a more reliable biomarker in certain clinical scenarios.
