D3.352 - Long-term analytical stability of ImmunoCAP tryptase supports enduring clinical interpretation thresholds

Serum tryptase is central to the diagnosis and monitoring of mast cell–related disorders. Widely adopted clinical decision thresholds were established using ImmunoCAP technology. Confidence in longitudinal comparability requires evidence of analytical stability during long-term frozen storage. We evaluated re-measurement consistency of archived sera stored at −20°C and compared 2026 results with historical measurements to confirm the continued validity of established interpretative values.

Archived Serum samples initially measured using the ImmunoCAP™ Tryptase test on the Phadia™ 250 instrument were subsequently re-assayed. and compared with historical results from 2009–2016 (n=95 paired samples). Paired differences were assessed using Wilcoxon signed-rank tests. Relative changes were evaluated on log-transformed data to derive geometric mean percent differences. Log Bland–Altman analysis with regression of log-difference on mean log concentration was used to assess proportional bias. Acceptability was interpreted against biological variation–derived bias specifications (desirable ≤8.11%; minimum ≤12.16%). Sensitivity analyses were performed to assess robustness.

No statistically significant paired difference was observed between historical measurements and 2026 re-analysis (Wilcoxon p=0.38). Geometric mean differences across periods ranged from approximately −4% to −10%. Log Bland–Altman analysis showed no evidence of proportional bias (slope −0.03, p=0.62). Observed differences were within analytical expectations for long-term frozen storage intervals of up to 15 years. Sensitivity analyses yielded consistent conclusions.

ImmunoCAP tryptase demonstrates sustained longitudinal analytical consistency after extended frozen storage. The absence of clinically meaningful drift confirms that diagnostic thresholds and interpretation frameworks historically established using ImmunoCAP Tryptase remain applicable today. This ensures continuity in patient care, allowing clinicians to interpret longitudinal and retrospective tryptase data with confidence, provided a well-validated and standardised assay is employed.