Ashrafzadeh-Kian, Susan

This cross-sectional study evaluates the performance of the US Food and Drug Administration–cleared phosphorylated tau 217 (p-tau217) to β-amyloid 42 ratio cut points used to detect amyloid pathology associated with Alzheimer disease.

AbstractINTRODUCTIONWe compare the stability of phosphorylated tau (p‐tau)217, amyloid beta (Aβ)42, Aβ40, Aβ42/40, and p‐tau217/Aβ42 at different storage temperatures.METHODSTen ethylenediaminetetraacetic acid–plasma sample aliquots stored at frozen, refrigerated, and ambient temperatures were tested at various timepoints up to 30 days. The mean percent change from baseline was calculated.RESULTSAβ42 and Aβ40 concentrations decreased by >15% after 6 hours at ambient temperature and after 24 hours refrigerated, while p‐tau217 remained stable over 72 hours with < 10% deviation from baseline at either storage temperature. The Aβ42/40 ratio remained relatively constant as each analyte concentration decreased concurrently, while the p‐tau217/Aβ42 ratio deviated from baseline over time. All biomarkers were stable up to 30 days frozen.DISCUSSIONDifferences in the stability of Aβ42 and p‐tau217 may lead to altered p‐tau217/Aβ42 ratio results if samples are not handled properly during the pre‐analytical testing phase. Ideally, samples should be frozen promptly and sent to the laboratory frozen.Highlights Plasma phosphorylated tau (p‐tau)217, amyloid beta (Aβ)42, Aβ40, Aβ42/40, and p‐tau217/Aβ42 stability was assessed. P‐tau217 was stable, but Aβ42 and Aβ40 started decreasing by 6 hours at ambient temperature. The analyte stability differences led to falsely increased p‐tau217/Aβ42 ratios. Increases > 15% were seen in p‐tau217/Aβ42 after 6 hours at ambient temperature or 24 hours at 4°C.

Abstract Objectives Assessment of surgical outcome in acromegaly is typically recommended at 3 to 6 months following surgery. The purpose of this study was to determine if insulin-like growth factor 1 (IGF-1) concentrations at 6 weeks were equally predictive of surgical outcomes compared with IGF-1 concentrations at 3 to 6 months postoperatively applying newer IGF-1 assays. Methods Retrospective review of patients with newly diagnosed acromegaly who had surgery between 2013 and 2020 and had postoperative IGF-1 measured by 6 weeks and 3 to 6 months. Results At 6 weeks, 20 (35%) of the total 57 had normal IGF-1 and became abnormal in 1 at 3 to 6 months, whereas 37 (65%) of 57 had abnormal IGF-1 concentrations at 6 weeks, which normalized in 1 patient by 3 to 6 months. In patients who changed clinical status, IGF-1 at 6 weeks was within ±0.1-fold of normal. Although a difference was seen between median IGF-1 concentrations (286 vs 267 ng/mL, P = .009) at 6 weeks and 3 to 6 months, the mean reduction was small (–19.9 ng/mL). Conclusions Compared with 3 to 6 months, use of IGF-1 at 6 weeks was associated with a change in clinical status in 3.5% of patients. Therefore, in most patients, IGF-1 at 6 weeks can be used to assess clinical outcome via newer assays.