Time- and temperature-dependent Pentraxin 3 stability in serum and bronchoalveolar lavage fluid samples

Pentraxin 3 (Ptx3) is an acute-phase protein that specifically targets fungal galactosaminogalactan and has been proposed as a promising biomarker for invasive fungal infections. However, its stability in clinical samples over time has not yet been established. This study aimed to evaluate the stability of Ptx3 in serum and bronchoalveolar lavage fluid (BALF) samples during mid- and long-term storage. A total of 44 serum and 52 BALF samples were examined or re-examined for Ptx3 concentrations using enzyme immunoassay in pooled and individual sample formats. Samples were stored at -80°C, -20°C, and +37°C for periods ranging from 0 to 56 months. Statistical analyses included a paired two-sample Wilcoxon signed-rank test, analysis of variance, Bonferroni test, and linear regression analysis. Ptx3 remained highly stable in serum and BALF samples for up to 8 months at -20°C, with variations ranging from -1.8% to +2.8%. Long-term stability was observed at -80°C for 48 months, followed by a slow decline in Ptx3 levels. In contrast, storage at +37°C resulted in rapid degradation, with a 36.5%-60.7% increase or a 92.9%-97% decrease in Ptx3 levels in serum and BALF, respectively. These findings confirm that Ptx3 is a stable and reliable biomarker for invasive fungal infections when appropriate storage conditions are maintained.