Bornhorst, Joshua A.

AbstractINTRODUCTIONThis study evaluated the performance of the Lumipulse plasma beta‐amyloid (Aβ) 42/40 and pTau181 compared to other assays to detect an abnormal amyloid‐positron emission tomography (PET).METHODSPlasma samples from cognitively unimpaired (N = 179) and MCI/AD dementia (N = 36) individuals were retrospectively evaluated. Plasma Aβ42/40 and pTau181 were measured using the Lumipulse and Simoa immunoassays. An immunoprecipitation mass spectrometry (IP‐MS) assay for plasma Aβ42/40 was also evaluated. Amyloid‐PET status was the outcome measure.RESULTSLumipulse and IP‐MS Aβ42/40 exhibited the highest diagnostic accuracy for detecting an abnormal amyloid‐PET (areas under the curve [AUCs] of 0.81 and 0.84, respectively). The Lumipulse and Simoa pTau181 assays exhibited lower performance (AUCs of 0.74 and 0.72, respectively). The Simoa Aβ42/40 assay demonstrated the lowest diagnostic accuracy (AUC 0.57). Combining Aβ42/40 and pTau181 did not significantly improve performance over Aβ42/40 alone for Lumipulse (AUC 0.83) or over pTau181 alone for Simoa (AUC 0.71)DISCUSSIONThe Lumipulse Aβ42/40 assay showed similar performance to the IP‐MS Aβ42/40 assay for detection of an abnormal amyloid‐PET; and both assays performed better than the two p‐tau181 immunoassays. The Simoa Aβ42/Aβ40 assay was the least accurate at predicting an abnormal amyloid‐PET status.Highlights Lumipulse plasma Aβ42/Aβ40 AUC for abnormal amyloid‐PET detection was 0.81. This performance was comparable to previously reported IP‐MS and higher than Simoa. Performance of Alzheimer's disease blood biomarkers varies between assays.

Abstract Background Interleukin 6 (IL-6) plays important roles in both innate and adaptive immunity, while dysregulated persistent production of IL-6 is involved in pathological development of various diseases associated with inflammation. Targeting the IL-6 pathway has led to many innovative treatment approaches. Siltuximab and Tocilizumab are monoclonal antibodies targeting IL-6 and IL-6 receptors respectively and have been FDA-approved for treatment of Castleman disease (Siltuximab), a rare lymphoproliferative disorder characterized by hyperproduction of IL-6 with an unknown prevalence, autoimmune diseases such as rheumatoid arthritis (Tocilizumab), and both shown potential as treatment for cytokine release syndrome in hospitalized COVID-19 patients. However, the presence of siltuximab can interfere with IL-6 assays, leading to the use of C-reactive protein (CRP) as a surrogate marker to monitor its efficacy. Aim To evaluate potential Siltuximab and Tocilizumab antibody interference on IL-6 measurements in three different IL-6 protein immunoassays. Method: Serum or EDTA plasma sample pools with different IL-6 concentrations ranging from low (2.3 – 11.1 pg/mL, around the reference interval cut-off for each assay) to high (18.5 – 1142 pg/mL), above reference interval cut-off for each assay) were utilized. Various concentrations of Siltuximab or Tocilizumab were spiked into the sample pools (at 10% of total volume) to achieve final concentrations up to 600 µg/mL and up to 300 µg/mL, respectively. Sample spiked with 10% saline were used as no-drug control. Three assays were used to measure IL-6 concentration: Beckman Access IL-6 assay on UniCel DxI 800 (Beckman Coulter), V-PLEX Plus human IL-6 assay on QuickPlex SQ120 (Meso Scale Diagnostics), and a Luminex cytokine panel assay developed in house (R&D systems) with upper reference interval limits of 6.4,1.8 and 5 pg/mL respectively. Results Siltuximab interfered with the measurement of IL-6 for all three assays. A significant interference (> 20% reduction) was observed at even a very low siltuximab concentrations in all three assays (0.05 µg/mL). In the presence of 5 µg/mL or greater Siltuximab, a maximum reduction of 93%, 83%, and 40% was observed for Beckman Access, R&D Luminex assay, and V-PLEX Plus Mesoscale assay, respectively. Tocilizumab did not interfere with the measurement of IL-6 in the three assays when serum was spiked with up to 300 µg/mL of the drug. Conclusion Siltuximab falsely reduce the measured IL-6 concentration on all three immunoassays tested in this study to differing degrees, whereas Tocilizumab does not. Consider the therapeutic range of Siltuximab (84 to 332 µg/mL) for treatment of Castleman disease, and a half-life of 20.6 days, measurement of IL-6 may not be useful in Siltuximab treated patients for an extended time-period.

OBJECTIVE Arginine vasopressin deficiency (AVD) following neurosurgical procedures for pituitary disorders is common and can delay discharge. Copeptin, a stable surrogate marker of arginine vasopressin, may predict postoperative AVD. The authors’ aim was to assess the optimal postoperative sampling time and cut-point concentration of copeptin to predict the development of postsurgical AVD. METHODS Adults without preexisting AVD who were undergoing surgery for a pituitary lesion between February 2020 and April 2022 were eligible for study inclusion. Two samples were drawn from each patient postoperatively to assess the copeptin concentration using an immunofluorescent assay. Samples were denoted as "early" (within 6 hours of extubation) or "postoperative day 1" (POD1; within 10–30 hours of extubation). Patients were evaluated for the development of AVD. RESULTS One hundred ninety-two patients (54.2% female) with a median age of 54.5 years (IQR 39.8–67.0 years) were included in the study. The median copeptin concentration at both time points was significantly lower in those with AVD (transient or permanent; n = 22, 11.5%) than in those without (early: 4.9 vs 18.7 pmol/L, p < 0.001; POD1: 3.4 vs 4.9 pmol/L, p < 0.001) but did not differ in those who developed transient versus permanent AVD. The optimal copeptin cut point for the prediction of AVD was < 8.5 pmol/L for early samples (sensitivity 0.70, specificity 0.80, positive predictive value [PPV] 0.29, negative predictive value [NPV] 0.96) and < 4.3 pmol/L for POD1 samples (sensitivity 0.82, specificity 0.63, PPV 0.22, NPV 0.96). In early samples, a copeptin cutoff of 22.9 pmol/L increased the sensitivity for the detection of AVD to 95% with an NPV of 99%. The proportion of patients who had AVD was higher (60.0% vs 8.8%, p < 0.001) and the copeptin concentration lower (early: 4.3 vs 17.0 pmol/L, p < 0.001; POD1: 2.7 vs 4.9 pmol/L, p < 0.001) among those who had undergone surgery for a craniopharyngeal duct pathology versus a pituitary adenoma. Although copeptin was lower in patients with persistent Cushing’s disease than in those in remission, the difference did not reach statistical significance (early p = 0.11, POD1 p = 0.52). Furthermore, the copeptin concentration could not predict the development of syndrome of inappropriate secretion of antidiuretic hormone. Patients without AVD who had received stress dose steroids intraoperatively had lower median early copeptin (11.7 vs 19.1 pmol/L, p = 0.027). CONCLUSIONS In early postoperative copeptin samples, the optimal copeptin cut point for AVD diagnosis was < 8.5 pmol/L, and a level > 22.9 pmol/L had predicative utility in excluding AVD. Caution should be used when interpreting copeptin results, as patients administered glucocorticoids intraoperatively without AVD had lower median copeptin concentrations.

Context.— Clinical testing for Wilson disease (WD) is potentially challenging. Measuring the fraction of labile bound copper (LBC) to total copper may be a promising alternative diagnostic tool with better sensitivity and specificity than some current biomarker approaches. A dual filtration–based inductively coupled mass spectrometry (ICP-MS) assay to measure LBC in serum was developed. Objective.— To establish a reference interval for LBC and LBC to total copper (LBC fraction) in a healthy adult population, and to examine associations between total copper, LBC, and LBC fraction with age, sex, menopausal status, hormone replacement therapy, and supplement use. Design.— Serum samples were collected from healthy male (n = 110) and female (n = 104) patients between the ages of 19 and 80 years. Total copper and LBC were analyzed using ICP-MS. Results were used to calculate the LBC fraction. Reference intervals were calculated for the 2.5th and 97.5th percentiles for both LBC and LBC fraction. Results.— The reference intervals for LBC were determined to be 13 to 105 ng/mL and 12 to 107 ng/mL for female and male patients, respectively. The reference intervals for the LBC fraction were 1.0% to 8.1% and 1.2% to 10.5% for female and male patients, respectively. No significant associations were found regarding age, menopausal status, hormone replacement therapy, or vitamin and supplement use. Conclusions.— Sex-specific reference intervals have now been established for LBC and LBC fraction. These data in conjunction with further testing of WD populations can be used to assess the sensitivity and specificity of LBC fraction in screening, monitoring, and diagnosis.

e16242 Background: Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) are rare cancers with highly heterogeneous growth rates, yielding very broad ranges of radiographic imaging intervals in standard guidelines, with a multitude of risk for patients. Better tools are needed to reduce risks for these patients. Chromogranin A (CgA) is released by GEP-NET cells and has been associated with increased tumor burden. The European Neuroendocrine Tumor Society (ENETS) considers CgA to be the most practical and useful general serum tumor marker in patients with NETs. However, clinical utility has been limited by the lack of prospective validation studies and by different sensitivity of CgA according to NET tumor type and volume. Accordingly, expert consensus guidelines have offered varying advice regarding the use of CgA to practicing clinicians. The aim was to evaluate the performance of the B·R·A·H·M·S CgA II KRYPTOR immunoassay to monitor the course of disease in patients with well-differentiated GEP-NETs (grade 1 and grade 2). This is the first prospective validation of a clinical algorithm for the interpretation of CgA values in patients with advanced GEP-NETs. Methods: This prospective, multi-center, observational study was designed to validate the performance of the B·R·A·H·M·S CgA II KRYPTOR assay in monitoring disease progression in a defined population of GEP-NET patients with minimal confounding from end organ dysfunction or concomitant medications (e.g. PPIs). Patients were followed for up to 36 months including the evaluation of tumor burden with RECIST 1.1 categorization by imaging (CT/MRI scans). A clinical cut-off for changes in CgA levels over time to indicate the risk that a tumor progression occurred was derived from a retrospective, bicentric observational pilot study. A change in CgA levels between visits was considered positive, if the CgA concentration increased by more than 50% to an absolute value of >100 ng/ml. Results: A total of 175 adult patients were enrolled, and 153 patients had measurable disease at baseline and ≥1 follow-up visit. Using the cut-off for CgA increase defined above resulted in a sensitivity of 34.4% (95%-CI: 25.6% - 44.3%, p < 0.001) and a specificity of 93.4% (95%-CI: 90.4% – 95.5%, p < 0.001). Positive predictive value (PPV), negative predictive value (NPV), positive likelihood ratio (LR+) and negative likelihood ratio (LR-) to diagnose whether a tumor progression occurred according RECIST 1.1 criteria were 57.9% (95% CI: 45.0-69.8), 84.3% (95% CI: 80.5-87.6), 5.20 (95% CI: 3.23-8.36), and 0.70 (95% CI: 0.61-0.81), respectively. The AUC was estimated at 0.731 (95% CI: 0.670-0.793). Conclusions: B·R·A·H·M·S CgA II KRYPTOR can be used in conjunction with other clinical methods as an aid in monitoring of disease progression during the course of disease and treatment in patients with gastroentero-pancreatic neuroendocrine tumors (GEP-NETs, grade 1 and grade 2).

Abstract Background Kidney stones are a highly prevalent disease worldwide. Additionally, both environmental and occupational exposure to Pb and Cd continue to be prevalent globally and can result in renal toxicity. The objective of this study was to examine the potential presence of Pb and Cd in kidney stones, and to assess for correlation with demographic factors including smoking, gender, age, and kidney stone matrix composition. Methods Patient kidney stones (n = 96) were analyzed using Fourier transform infrared spectroscopy to identify the stone constituents. Cd and Pb concentrations (µg/g) were determined by inductively coupled plasma mass spectrometry. Cd and Pb concentrations were correlated using bivariable and multivariable statistical analysis with demographic factors (age, gender, smoking status), and kidney stone composition. Results Kidney stone Cd (median 0.092 µg/g, range 0.014 to 2.46) and Pb concentrations (median 0.95 µg/g, range 0.060 to 15.4) were moderately correlated (r = 0.56, P &lt; 0.0001). Cd concentrations were positively associated with patient history of smoking, patient age, and calcium oxalate monohydrate levels while negatively associated with struvite and uric acid/uric acid dihydrate. Pb concentrations were positively associated with females and apatite levels while negatively associated with uric acid/uric acid dihydrate. After holding constant other stone type composition levels, smoking status, and age, both Pb and Cd were positively associated with apatite and negatively associated with uric acid/uric acid dihydrate, struvite, and calcium carbonate. Conclusions Cd and Pb kidney stone concentrations are associated with specific kidney stone types. Cd and Pb kidney stone concentrations are both associated with smoking.

AbstractContextThyroglobulin autoantibodies (TgAbs) affect thyroglobulin immunometric assays (TgIMAs), causing falsely low results. Conversely, heterophilic antibodies (HAs) may cause falsely elevated results. Thyroglobulin (Tg) measurements by mass spectrometry (MS) resist antibody interference. The most effective use of TgIMA/TgMS in the evaluation of Tg remains unclear.ObjectiveThe objective of this work was to study the usefulness of TgMS vs TgIMA in the presence of Tg measurement interference by HA and TgAb.MethodsIn 163 thyroid cancer patients, Tg was postoperatively measured by TgIMA and TgMS. When TgIMA was elevated and TgMS undetectable, HA was assessed by serial dilution and pretreatment with HA blocking reagent. TgIMA and TgMS were compared in TgAb-positive patients with well-characterized clinical status.Results6 out of 45 cases with TgIMA &gt;1 ng/mL had undetectable TgMS. HA interference was confirmed by serial dilution and HA blocking reagent addition. In TgAb-positive cases, TgIMA and TgMS were highly correlated (R2 = 0.86). In patients with structural disease and TgAb, TgIMA and TgMS were detectable in 6/19 patients, and 9/19 cases, respectively. The TgMS concentration range in the 3 discrepant cases ranged from 0.5 to 2.0 ng/mL. Hence, the presence of TgAb was associated with inappropriately reduced Tg concentrations with both TgIMA and TgMS.ConclusionHA cause falsely elevated TgIMA with undetectable TgMS with significant frequency. TgMS can be used to rule out HA interference. Albeit resistant to TgAb in vitro, TgMS detects little Tg in patients with TgAb and structural disease. Hence, TgAb may reduce Tg concentrations in vivo. The implication is that no assay design may be able to overcome this problem. TgMS may not detect structural disease in TgAb-positive patients.

AbstractObjectiveTo investigate the effect of CRYSVITA® (burosumab‐twza) on FGF23 measurements in an intact and a C‐terminal immunoassay.MethodsAn intact serum FGF23 (MedFrontier) and a C‐terminal plasma FGF23 assay (Immutopics) were used. Serum/plasma pools were spiked to span the burosumab therapeutic range (1.4–11.3 μg/ml) and FGF23 recovery was assessed. Patient serum and plasma samples obtained pre and post‐burosumab treatment were evaluated on both assays and compared with corresponding phosphorus measurementsResultsSpiking burosumab (1.4–11.3 μg/ml) into sample pools resulted in a dose‐dependent negative analytical interference on intact FGF23 measurements and no significant interference for C‐terminal FGF23 measurements. However, more than a 500‐fold median increase (post‐ vs. pre‐burosumab administration) in in vivo FGF23 concentrations were observed by both assays.ConclusionsTherapeutic concentrations of burosumab result in a negative analytical interference of the intact, but not the C‐terminal FGF23 immunoassay. Despite this in vitro analytical interference in the intact assay, relatively large elevations of both intact FGF23 and C‐terminal FGF23 measurements were observed in vivo following burosumab administration. Following burosumab administration, FGF23 measurements must be interpreted within the clinical context of the patient and other relevant biomarker results.SummaryThis article describes a negative analytical interference by burosumab in an intact FGF23 immunoassay. The recovery of C‐terminal FGF23 is not significantly affected by the presence of burosumab. In vivo, both assays demonstrate extreme FGF23 elevations in the presence of the drug. Furthermore, the measurement of FGF23 blocked by burosumab is not clinically useful regarding hypophosphataemia.