Neurofilament light chain is elevated in patients with newly diagnosed idiopathic intracranial hypertension: A prospective study.

BACKGROUND: Idiopathic intracranial hypertension is a secondary headache disorder potentially causing visual loss. Neurofilament light chain is a candidate, prognostic biomarker, but further studies of neuronal biomarkers are needed. Our objective was to investigate neurofilament light chain in cerebrospinal fluid (cNfL) and plasma (pNfL), amyloid-beta 42 (Aß-42), total-tau and phosphorylated-tau in cerebrospinal fluid in new-onset idiopathic intracranial hypertension. METHODS: Prospective case-control study including new-onset idiopathic intracranial hypertension and age, sex and BMI matched controls. Biomarkers were compared between patients and controls and related to papilledema, visual fields and opening pressure. RESULTS: We included 37 patients and 35 controls. Patients had higher age-adjusted cNfL (1.4 vs. 0.6 pg/mL, p-adjusted < 0.001), pNfL (0.5 vs. 0.3 pg/mL, p-adjusted < 0.001) and total-tau/Aß-42 (0.12 vs. 0.11, p-adjusted = 0.039). Significant, positive linear correlations were found between cNfL, pNfL, total-tau/Aß-42 and opening pressure. Patients with severe papilledema had elevated cNfL compared to mild-moderate papilledema (median cNfL: 4.3 pg/mL (3.7) versus 1.0 pg/mL (1.4), p-adjusted = 0.009). cNFL was inversely associated with perimetric mean deviation (r = -0.47, p-adjusted < 0.001). CONCLUSIONS: cNfL, pNfL and total-tau/Aß-42 were elevated in new-onset idiopathic intracranial hypertension. cNfL was associated with severity of papilledema and visual field defects at diagnosis. This indicates early axonal damage. Neurofilament light chain is a candidate biomarker for disease severity.

Establishing a pediatric reference interval for plasma calprotectin.

Plasma calprotectin is a promising new biomarker of inflammatory activity and has been found to correlate well with clinical and endoscopic activity in children and adolescents with inflammatory bowel disease. A pediatric reference interval for plasma calprotectin has not been established for the Phadia 250 EliA™ Calprotectin fluoroenzyme immunoassay. In studies regarding pre-analytical properties, excellent precision and stability was found. However, sensitivity to hemolysis was demonstrated. We identified pediatric blood samples from apparently healthy children who were referred by their general practitioner for blood sampling including measurement of hemoglobin (Hb) and C-reactive protein (CRP). We excluded samples from children who had undergone additional blood sampling within 2 months before or after the index sample, if Hb was outside of local reference ranges or CRP levels were above the lower limit of the measuring interval (LLM), and any samples with a hemolysis above 0.02 mmol/L. Using this algorithm, we identified 141 blood samples. No outliers were identified. We established the following reference intervals according to CLSI C28-A3 using non-parametric statistics: 1-17 years: 16-246 µg/L. Our results may prove useful for further utilization of plasma calprotectin as a marker of inflammation in children and adolescents with inflammatory disorders.

Longitudinal Change in Serum Neurofilament Light Chain in Type 2 Diabetes and Early Diabetic Polyneuropathy: ADDITION-Denmark.

OBJECTIVE: To investigate the longitudinal development of neurofilament light chain (NfL) levels in type 2 diabetes with and without diabetic polyneuropathy (+/-DPN) and to explore the predictive potential of NfL as a biomarker for DPN. RESEARCH DESIGN AND METHODS: We performed retrospective longitudinal case-control analysis of data from 178 participants of the Anglo-Danish-Dutch Study of Intensive Treatment in People with Screen-Detected Diabetes in Primary Care-Denmark (ADDITION-Denmark) cohort of people with screen-detected type 2 diabetes. Biobank samples acquired at the ADDITION-Denmark 5- and 10-year follow-ups were analyzed for serum NfL (s-NfL) using single-molecule array, and the results were compared with established reference material to obtain NfL z-scores. DPN was diagnosed according to Toronto criteria for confirmed DPN at the 10-year follow-up. RESULTS: s-NfL increased over time in +DPN (N = 39) and -DPN participants (N = 139) at levels above normal age-induced s-NfL increase. Longitudinal s-NfL change was greater in +DPN than in -DPN participants (17.4% [95% CI 4.3; 32.2] or 0.31 SD [95% CI 0.03; 0.60] higher s-NfL or NfL z-score increase in +DPN compared with -DPN). s-NfL at the 5-year follow-up was positively associated with nerve conduction studies at the 10-year follow-up (P = 0.02 to <0.001), but not with DPN risk. Areas under the curve (AUCs) for s-NfL were not inferior to AUCs for the Michigan Neuropathy Screening Instrument questionnaire score or vibration detection thresholds. Higher yearly s-NfL increase was associated with higher DPN risk (odds ratio 1.36 [95% CI 1.08; 1.71] per 1 ng/L/year). CONCLUSIONS: Our findings suggest that preceding s-NfL trajectories differ slightly between those with and without DPN and imply a possible biomarker value of s-NfL trajectories in DPN.

Neurofilament Light Chain and Glial Fibrillary Acidic Protein as early prognostic biomarkers after out-of-hospital cardiac arrest.

AIMS: Neurofilament Light Chain (NfL) and Glial Fibrillary Acidic Protein (GFAP) are proteins released into the bloodstream upon hypoxic brain injury. We evaluated the biokinetics and examined the prognostic performance of serum NfL and GFAP in comatose out-of-hospital cardiac arrest (OHCA) patients. Furthermore, we compared the prognostic performance to that of serum Neuron Specific Enolase (NSE). METHODS: This is a sub-study of the "Targeted temperature management for 48 vs 24 hours" (NCT01689077) trial. NfL and GFAP serum values from 82 patients were examined in blood samples collected at 24, 48 and 72 hours (h) after reaching target temperature of 33 ± 1 °C. This temperature was reached within a median of 281-320 minutes after intensive care unit admission. GFAP was analysed at 48 and 72 h. The neuroprognostic performance of NfL and GFAP was evaluated after 6 months follow-up. RESULTS: NfL and GFAP values were significantly higher in patients with a poor outcome (Cerebral Performance Category (CPC) score 3-5) vs. good outcome (CPC 1-2). NfL 24 h: 1371.5 (462.0; 2125.1) vs. 24.8 (14.0; 61.6). GFAP 48 h: 1285.3 (843.9; 2236.7) vs. 361.2 (200.4; 665.6) (both p < 0.001). Both biomarkers were promising markers of poor functional outcome at 24 and 48 h respectively: NfL 24 h: AUROC 0.95 (95% CI: 0.91-1.00). GFAP 48 h: AUROC 0.88 (95% CI: 0.81-0.96). NfL and GFAP both predicted outcome better than NSE at 48 h (both p < 0.01). At 72 h NfL but not GFAP outperformed NSE (p = 0.01). CONCLUSION: Serum NfL and GFAP may be strong biomarkers of poor functional outcome after OHCA from an early timepoint.

Neurofilament light chain: serum reference intervals in Danish children aged 0-17 years.

Elevated levels of neurofilament light chain (NfL) in the blood is an unspecific biomarker for damage to neuronal axons. The measurement of NfL levels in the blood can provide useful information for monitoring and prognostication of various neurological disorders in children, but a reference interval (RI) is needed before the clinical implementation of the biomarker. We aimed to establish a RI for children aged 0-17 years. Serum samples from 292 healthy reference subjects aged 0.4-17.9 years were analysed by a single-molecule array (Simoa®) established for routine clinical use. Non-parametric quantile regression was used to model a continuous RI, and a traditional age-partitioned non-parametric RI was established according to Clinical and Laboratory Standard Institute (CLSI) guideline C28-A3. Furthermore, we investigated the effect of hemolysis on assay performance. The traditional age-partitioned non-parametric RI for the age group <3 years was 3.5-16.6 ng/L and 2.1-13.9 ng/L in the age group ≥3 years, respectively. The continuous RI showed an age-dependent decrease in median NfL levels in the first three years of life which was also evident in the age-partitioning of the traditional RI. We found no difference between sexes and no impact of hemolysis on the NfL test results. This study establishes a pediatric RI for serum NfL and lays the groundwork for its future use in clinical practice.

Reference intervals and stability of haptocorrin and holotranscobalamin in Danish children and elderly.

BACKGROUND: Haptocorrin (HC) and holotranscobalamin (holoTC) carry vitamin B12 (B12) in the circulation and can be useful biomarkers for evaluating B12 status. The concentration of both proteins depends on age, but data on reference intervals for children and the elderly are sparse. Similarly, not much is known about the effect of preanalytical factors. METHODS: HC plasma samples from healthy elderly > 65 years (n = 124) were analysed, and both HC and holoTC were analysed in paediatric serum samples ≤ 18 years (n = 400). Furthermore, we investigated assay precision and stability. RESULTS: HC and holoTC were effected by age. We established reference intervals for HC: 2-10 years, 369-1237 pmol/L; 11-18 years, 314-1128 pmol/L; 65-82 years, 242-680 pmol/L and for holoTC: 2-10 years, 46-206 pmol/L; 11-18 years, 30-178 pmol/L. Analytical coefficients of variations of 6.0-6.8% and 7.9-15.7% were found for HC and holoTC, respectively. HC were affected when stored at room temperature and by freeze/thaw. HoloTC was stable at room temperature and after delayed centrifugation. CONCLUSION: We present novel 95% age-related reference limits for HC and HoloTC in children, and for HC both in children and elderly. Moreover, we found HoloTC to be fairly stable when stored, whereas HC was more vulnerable to preanalytical factors.

Serum GFAP - pediatric reference interval in a cohort of Danish children.

OBJECTIVES: Glial fibrillary acidic protein (GFAP) in blood is an emerging biomarker of brain injury and neurological disease. Its clinical use in children is limited by the lack of a reference interval (RI). Thus, the aim of the present study was to establish an age-dependent continuous RI for serum GFAP in children. METHODS: Excess serum from routine allergy testing of 391 children, 0.4-17.9 years of age, was measured by a single-molecule array (Simoa) assay. A continuous RI was modelled using non-parametric quantile regression and presented both graphically and tabulated as discrete one-year RIs based on point estimates from the model. RESULTS: Serum GFAP showed a strong age-dependency with declining levels and variability from infants to adolescents. The estimated median level decreased 66 % from four months to five years of age and another 65 % from five years to 17.9 years of age. No gender difference was observed. CONCLUSIONS: The study establishes an age-dependent RI for serum GFAP in children showing high levels and variability in the first years of life.

Diagnostic Cut-offs for CSF ß-amyloid and tau proteins in a Danish dementia clinic.

BACKGROUND: Analysis of beta-amyloid 1-42 (Aß42), total tau (t-tau) and phosphorylated-tau 181 (p-tau) in the cerebrospinal fluid (CSF) is often performed as a part of the diagnostic work-up in case of suspected Alzheimer's dementia (AD). Unfortunately, studies on optimal CSF biomarker cut-offs in a real-world clinical setting are scarce. METHODS: We retrospectively evaluated the biomarker levels of 264 consecutive patients referred to our dementia clinic. The biomarkers were analysed with the Elecsys(R) assays. Diagnoses were based on all available clinical information, including FDG-PET scans. RESULTS: In total, we identified 233 patients diagnosed with dementia. The median MMSE score was 22 (IQR 18-25). AD pathophysiology was suspected in 156 patients, and the corresponding cut-offs based on the Youden index were: Aß42: 903 ng/L (ROC-AUC 0.78); t-tau: 272 ng/L (ROC-AUC 0.78); p-tau: 24 ng/L (ROC-AUC 0.85); t-tau/Aß42 ratio: 0.34 (ROC-AUC 0.91); p-tau/Aß42 ratio: 0.029 (ROC-AUC 0.92). CONCLUSIONS: We found the tau/Aß42 ratios to possess the best diagnostic performance, but our estimated cut-off values for the ratios were somewhat higher than previously reported. Consequently, if the CSF analyses are used to support a diagnosis of AD in a heterogeneous high-prevalence cohort, adjustment of the cut-offs may be warranted.

Serum neurofilament light chain - A potential biomarker for polyneuropathy in type 2 diabetes?

AIMS: To investigate the relationship between neurofilament light chain (NfL) and the presence and severity of diabetic polyneuropathy (DPN). METHODS: We performed cross-sectional analysis of data from 178 participants of the ADDITION-Denmark cohort of people with screen-detected type 2 diabetes and 32 healthy controls. Biobank serum samples were analyzed for NfL using single-molecule array. DPN was defined by Toronto criteria for confirmed DPN. Original and axonal nerve conduction study (NCS) sum z-scores were used as indicators of the severity of DPN and peripheral nerve damage. RESULTS: 39 (21.9%) participants had DPN. Serum NfL (s-NfL) was significantly higher in participants with DPN (18.8 ng/L [IQR 14.4; 27.9]) than in participants without DPN (15.4 ng/L [IQR 11.7; 20.1]). There were no unadjusted s-NfL differences between controls (17.6 ng/L [IQR 12.7; 19.8]) and participants with or without DPN. Higher original and axonal NCS sum z-scores were associated with 10% higher s-NfL (10.2 and 12.1% [95% CI's 4.0; 16.8 and 6.6; 17.9] per 1 SD). The AUC of s-NfL for DPN was 0.63 (95% CI 0.52; 0.73). CONCLUSIONS: S-NfL is unlikely to be a reliable biomarker for the presence of DPN. S-NfL is however associated tothe severity of the nerve damage underlying DPN.

Serum GFAP - reference interval and preanalytical properties in Danish adults.

OBJECTIVES: Glial fibrillary acidic protein (GFAP) is a promising biomarker that could potentially contribute to diagnosis and prognosis in neurological diseases. The biomarker is approaching clinical use but the reference interval for serum GFAP remains to be established, and knowledge about the effect of preanalytical factors is also limited. METHODS: Serum samples from 371 apparently healthy reference subjects, 21-90 years of age, were measured by a single-molecule array (Simoa) assay. Continuous reference intervals were modelled using non-parametric quantile regression and compared with traditional age-partitioned non-parametric reference intervals established according to the Clinical and Laboratory Standards Institute (CLSI) guideline C28-A3. The following preanalytical conditions were also examined: stability in whole blood at room temperature (RT), stability in serum at RT and -20 °C, repeated freeze-thaw cycles, and haemolysis. RESULTS: The continuous reference interval showed good overall agreement with the traditional age-partitioned reference intervals of 25-136 ng/L, 34-242 ng/L, and 5-438 ng/L for the age groups 20-39, 40-64, and 65-90 years, respectively. Both types of reference intervals showed increasing levels and variability of serum GFAP with age. In the preanalytical tests, the mean changes from baseline were 2.3% (95% CI: -2.4%, 6.9%) in whole blood after 9 h at RT, 3.1% (95% CI: -4.5%, 10.7%) in serum after 7 days at RT, 10.4% (95% CI: -6.0%, 26.8%) in serum after 133 days at -20 °C, and 10.4% (95% CI: 9.5%, 11.4%) after three freeze-thaw cycles. CONCLUSIONS: The study establishes age-dependent reference ranges for serum GFAP in adults and demonstrates overall good stability of the biomarker.

Short-term biological variation of serum glial fibrillary acidic protein.

OBJECTIVES: Serum glial fibrillary acidic protein (GFAP) is an emerging biomarker for intracerebral diseases and is approved for clinical use in traumatic brain injury. GFAP is also being investigated for several other applications, where the GFAP changes are not always outstanding. It is thus essential for the interpretation of GFAP to distinguish clinical relevant changes from natural occurring biological variation. This study aimed at estimating the biological variation of serum GFAP. METHODS: Apparently healthy subjects (n=33) had blood sampled for three consecutive days. On the second day, blood was also drawn every third hour from 9 AM to 9 PM. Serum GFAP was measured by Single Molecule Array (Simoa™). Components of biological variation were estimated in a linear mixed-effects model. RESULTS: The overall median GFAP value was 92.5 pg/mL (range 34.4-260.3 pg/mL). The overall within- (CVI) and between-subject variations (CVG) were 9.7 and 39.5%. The reference change value was 36.9% for an increase. No day-to-day variation was observed, however semidiurnal variation was observed with increasing GFAP values between 9 AM and 12 PM (p<0.00001) and decreasing from 12 to 9 PM (p<0.001). CONCLUSIONS: Serum GFAP exhibits a relatively low CVI but a considerable CVG and a marked semidiurnal variation. This implies caution on the timing of blood sampling and when interpreting GFAP in relation to reference intervals, especially in conditions where only small GFAP differences are observed.

Plasma calprotectin - preanalytical stability and interference from hemolysis.

As an activation product of neutrophil granulocytes, calprotectin has been widely used in fecal samples for diagnosis and monitoring of patients with inflammatory bowel disease. However, fecal sample collection is cumbersome, and pre-analytical sources of error are plentiful. Therefore, plasma calprotectin is being investigated as a promising new biomarker. To utilize any biomarker, pre-analytical factors such as stability and susceptibility to interference from hemolysis must be established. We present precision estimates, stability results as well as interference study on plasma calprotectin in EDTA-plasma using the Thermo Fischer Phadia 250 EliATM Calprotectin immunoassay. Precision was estimated by the use of patient pools as well as internal quality controls provided by the manufacturer. Coefficients of variance were below 6.9% for patient samples. Calprotectin was stable in EDTA plasma after storage at 5-8 °C for up to 4 days, as well as after long-term storage at -20 °C. Susceptibility to interference from hemolysis was high, especially for low concentrations of calprotectin (<50 ng/mL) where hemoglobin levels above 0.02 mmol/L lead to false increase in calprotectin concentrations of up to 100%.

Vitamin B12 deficiency: correction of P-methylmalonic acid for estimated glomerular filtration rate to improve diagnostic value - a confirmatory study.

Objectives: For diagnosis of vitamin B12 deficiency, plasma methylmalonic acid (P-MMA) is considered superior to plasma vitamin B12 (P-B12). Reduced kidney function elevates P-MMA, hence, hampering P-MMA as a biomarker. We assessed whether correcting P-MMA for estimated glomerular filtration rate (eGFR) can affect the estimated prevalence of B12 deficiency. Methods: We included 115,245 patients with concomitant measurements of P-MMA, P-B12 and P-Creatinine. B12 deficiency was classified using P-MMA decision limits at >0.75 and >0.43 µmol/L. The non-linear relation between eGFR and P-MMA was estimated using spline regression. We calculated the percentage-wise reclassification of B12 deficiency by using an eGFR corrected P-MMA formula with eGFR reference points of 90 and 60 mL/min. Results: 6% with B12 deficiency were reclassified as non-deficient after adjusting for eGFR (reference point eGFR 90 mL/min) with both P-MMA decision limits. Overall B12 deficiency prevalence was reduced from 9.6% to 9.0% (P-MMA decision limit 0.43 µmol/L). With P-MMA decision limits at 0.75 and 0.43 µmol/L, 33.6% and 44.8% of B12 deficient patients with an eGFR <60 mL/min were reclassified as non-deficient. Conclusions: We have demonstrated that correcting P-MMA for eGFR can reclassify P-MMA levels across decision limits for diagnosing B12 deficiency, in particular for patients with reduced kidney function. This may have clinical implications for avoiding overdiagnosis of this chronic disease.

Biotin interference in routine IDS-iSYS immunoassays for aldosterone, renin, insulin-like growth factor 1, growth hormone and bone alkaline phosphatase.

Biotin is increasingly used as dietary supplement. As many immunoassays rely on a binding between biotin and streptavidin, intake of biotin may interfere with laboratory tests, leading to spurious test results. We examined the extent to which levels of aldosterone, renin, insulin-like growth factor 1 (IGF-1), growth hormone (GH) and bone alkaline phosphatase (BAP) were affected by biotin. In an experimental study performed at Aarhus University Hospital, Denmark, patient samples (plasma or serum) were pooled and spiked with biotin in increasing concentrations (0, 20, 50, 100 and 500 ng/mL). All biomarkers were analyzed using Immunodiagnostic Systems (IDS-iSYS) Multi-Discipline Automated System assays. The average bias (%) was calculated, as the difference in concentrations between the sample without biotin (reference) and the samples with increasing concentrations of biotin. Both aldosterone and renin assays showed substantial biotin interference in a dose-dependent manner, with biases up to +3484% for aldosterone and -98% for renin in the highest concentrations of biotin (100-500 ng/mL). IGF-1, GH and BAP results were generally less affected by added biotin and significant bias (>10%) was observed only when the biotin concentration was 100 ng/mL (IGF-1 and GH) or 500 ng/mL (BAP). In conclusion, biotin interfered with the IDS-iSYS immunoassays, particularly for aldosterone and renin. The assays for GH, IGF-1 and BAP were less sensitive and only with high concentrations of biotin.

Reference intervals for plasma vitamin B12 and plasma/serum methylmalonic acid in Danish children, adults and elderly.

BACKGROUND: Plasma/serum vitamin B12 (B12) is often used to screen for B12 deficiency complemented with analysis of methylmalonic acid (MMA) in case of low B12. The concentration of both analytes likely depends on age, and we, therefore, aimed at establishing 95% age-adjusted reference intervals (RIs) for plasma B12 and serum/plasma MMA in the Danish population. METHODS: We collected and analysed blood samples from healthy children, adults, and elderly individuals and extracted routine clinical B12 and MMA results to establish RIs. We also evaluated the association between matching B12 and MMA results. RESULTS: We suggest the following RIs for plasma B12 and plasma/serum MMA, respectively. 0-<1 year: 180-1400 pmol/L, 0.10-1.25 µmol/L; 1-<11 years: 260-1200 pmol/L, 0.10-0.30 µmol/L; 12-<18 years: 200-800 pmol/L, 0.10-0.35 µmol/L; 18-<65 years: 200-600 pmol/L, 0.10-0.40 µmol/L; 65 + years: 200-600 pmol/L, 0.12-0.46 µmol/L. Finally, the proportion of patients with elevated MMA differed between age groups independently of B12 and was highest in children. CONCLUSION: We propose new age-adjusted RIs for B12 and MMA and suggest that age-dependent cut-off values should be implemented if plasma B12 is used to screen for B12 deficiency.

Procollagen III, N-terminal propeptide (PIIINP): establishment of reference intervals in Northern European adults and children using the MAGLUMI 800 chemiluminescence immunoassay.

Procollagen III, N-terminal propeptide (PIIINP) is used as a biomarker for increased collagen III-synthesis. Reference intervals have not been established for the MAGLUMI 800 chemiluminescence immunoassay (CLIA) in Northern European adults or in children. The present study aimed to establish age-specific reference intervals in a Northern European population. PIIINP serum levels were analysed in healthy blood donors 19-67 years (n = 240) and children 2-18 years (n = 420). Furthermore, we investigated total imprecision and stability at room temperature and at -20 °C and performed a method comparison between MAGLUMI 800 CLIA (Snibe Diagnostics, Shenzhen, China) and ADVIA Centaur CP (Siemens Healthcare Diagnostics, Tarrytown, NY,USA). PIIINP was influenced by age but not sex. We established the following reference intervals: 2-10 years, 18-62 µg/L; 11-18 years, 15-75 µg/L; 19-39 years, 15-55 µg/L; 40-67 years, 14-31 µg/L. Total imprecision for PIIINP on MAGLUMI 800 was acceptable with coefficients of variation of 4.9% in the low range and 9.4% in the high range. PIIINP was stable for 24 h at room temperature after centrifugation and for at least 7 months at -20 °C. MAGLUMI 800 yielded significantly higher PIIINP levels than ADVIA Centaur CP. In conclusion, we established age-specific reference intervals for PIIINP using MAGLUMI 800 CLIA in a large Danish cohort. Our results may be useful for other laboratories wishing to establish PIIINP on the same platform and may provide improved guidance for medical doctors treating both children and adults with fibrotic disorders.

Anti-transglutaminase IgA antibody measurement in coeliac disease: Method comparison IDS-iSYS vs. Thermo Fisher Phadia.

In coeliac disease, the diagnostic work-up is based on a combination of clinical, histopathological and serological evaluation. Among the serological tests, the presence of tissue transglutaminase (tTG) IgA antibodies is the cornerstone owed to a high sensitivity and specificity. Recently, Immunodiagnostic Systems Ltd (IDS) introduced the fully automated chemiluminescent autoimmune assays for use on the IDS-iSYS Multi-Discipline Automated System. In this study, we aimed to compare the performance of the IDS-iSYS assay to the Thermo Fisher Phadia assay and to establish the upper reference limit of tTG IgA in a healthy population from Denmark based on the IDS-iSYS assay. We discovered a total imprecision of CV = 12.2% (2.87 AU/mL) and CV = 10.6% (47.55 AU/mL). Moreover, we compared the performance of IDS-iSYS assay to Thermo Fisher Phadia assay in 236 samples from unselected patients submit for tTG IgA testing and found a concordance of 97% (p < .0001). Furthermore, in 150 healthy blood donors, we established the upper reference limit of 3.26 AU/mL (95% CI: 3.10 - 3.90) was identified. Our study validates the performance of the IDS-iSYS tTG IgA assay and demonstrates results in concordance with the established Thermo Fisher Phadia. Furthermore, it provides estimates for the upper reference interval limit of the tTG-IgA.

Reference interval and preanalytical properties of serum neurofilament light chain in Scandinavian adults.

The neurofilament light chain (NfL) is a promising biomarker of neuronal injury which is approaching routine clinical use. With the development of ultra-sensitive technologies, NfL has become measurable in the peripheral blood but the reference interval for serum NfL remains to be established. NfL was measured by a single-molecule array (Simoa™) analysis under internal and external quality control which is established for routine clinical use. Serum samples from 342 reference subjects, 18-87 years were analyzed. The age-partitioned reference interval was established according to Clinical and Laboratory Standards Institute guidelines, an approximation of the upper reference interval limit per 10-year age-groups was performed, and key pre-analytical properties were examined. Serum NfL levels increased 2.9% per year. The non-parametric reference interval for the age groups 18-40, 41-65, and >65 years were 2.8-9.7 ng/L, 4.6 - 21.4 ng/L, and 7.5-53.8 ng/L, respectively. The estimated upper reference interval limits per 10-year intervals corresponded well with the 90% confidence limits of the non-parametric reference interval. The recovery of serum NfL after seven days at room temperature or three freeze-thaw cycles were 93% (95% CI: 89%-97%) and 92% (95% CI: 83%-102%) and levels in serum were only slightly higher than levels in plasma (p < .0001). The study establishes the serum NfL reference interval, provide estimated upper reference intevral limits in 10-year intervals to increase the clinical applicability and uncover pre-analytical properties that make serum NfL feasible for clinical use.

Plasma neurofilament light chain is associated with mortality after spontaneous intracerebral hemorrhage.

Background Neurofilament light chain (NfL) is a neuron-specific biomarker with prognostic ability in several types of central nervous system injuries. This study investigates if plasma NfL (pNfL) is elevated early after spontaneous intracerebral hemorrhage (ICH) and whether such elevation reflects disease severity and day-30 outcome. Methods pNfL was quantified by single molecule array analysis in 103 reference subjects (RS) and in samples from 37 patients with ICH obtained on admission to hospital and at 24-h follow-up. The primary outcome was day-30 mortality. Clinical status on admission was evaluated by standardized scoring systems. Results Median pNfL among RS was 9.6 (interquartile range [IQR] 6.2) pg/mL. Upon admission, ICH patients had pNfL of 19.8 (IQR 30.7) pg/mL increasing to 35.9 (IQR 44.5) pg/mL at 24 h (all, p < 0.001). On admission, pNfL was higher among ICH non-survivors than survivors (119.2 [IQR 152.6] pg/mL vs. 15.7 [IQR 19.6] pg/mL, p < 0.01) and this difference was observed also on 24 h follow-up (195.1 [IQR 73.9] pg/mL vs. 31.3 [IQR 27.8] pg/mL, p < 0.01). The area under the receiver operating characteristic curve (ROC AUC) for discrimination of day-30 mortality was significant on admission (AUC = 0.83, 95% confidence interval [CI]: 0.56-1.0) and increased on 24-h follow-up (AUC = 0.93, 95% CI: 0.84-1.0). The odds ratio (OR) for death, by each quartile increase in pNfL was significant both on admission (OR = 4.52, 95% CI: 1.32-15.48) and after 24-h follow-up (OR = 9.52, 95% CI: 1.26-71.74). Conclusions PNfL is associated with day-30 mortality after spontaneous ICH when early after the ictus.