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.

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.

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 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.

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%.

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.

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.

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.

Comparison of three competitive immunoassays for measurement of TSH receptor antibodies in patients with Graves' disease.

Thyrotropin (TSH) receptor antibodies (TRAb) mediate the hyperthyroidism of Graves' disease (GD). The aim of the study was to compare the diagnostic performance and assay agreement between three immunoassays for the measurement of TRAb in patients with newly diagnosed GD. TRAb was measured with three different assays [H-TRAb (BRAHMS Diagnostica), M22-Man (RSR Limited) and M22-Aut (Roche Diagnostics)] in 387 participants who were recruited from two Danish population-based studies and diagnosed with GD (n = 101), multinodular toxic goitre (n = 88), primary autoimmune hypothyroidism (n = 100) or included as controls (n = 98). Coefficient of variation for duplicate measurements with each of the three assays were H-TRAb: 3.6%, M22-Man: 9.4%, M22-Aut: 7.7%. Frequency of TRAb positivity in patients with GD were H-TRAb: 95%, M22-Man: 94%, M22-Aut: 96%. Receiver operating characteristic analysis revealed a high sensitivity (H-TRAb: 95%, M22-Man: 93%, M22-Aut: 95%) and specificity (H-TRAb: 99%, M22-Man: 99%, M22-Aut: 97%) for the diagnosis of GD with all assays. Comparison of TRAb levels showed inter-assay variability and values were considerably lower with the M22-Man assay. All TRAb assays showed a high diagnostic performance for GD, but a high inter-assay variability was observed limiting the use of different assays in clinical monitoring of patients with GD.

Whole blood samples for adrenocorticotrophic hormone measurement can be stored at room temperature for 4 hours.

INTRODUCTION: The aim of this study was to investigate and compare the stability of adrenocorticotrophic hormone (ACTH) in whole blood stored on ice and at room temperature for up to 48 hours. This study differs from previous studies by a larger data material. MATERIALS AND METHODS: EDTA-blood samples from 30 patients were collected, aliquoted and stored on ice or at room temperature for 0, 2, 4, 24, or 48 h before centrifugation, and the plasma was stored frozen until analysis. All samples were analyzed using an automated electrochemiluminescence immunoassay on cobas 6000 e601. The change in ACTH concentration was illustrated as ACTH recovery compared to standard conditions defined as samples stored immediately on ice, centrifuged and plasma frozen within 1 h. A change in ACTH concentration of more than 10% was considered to be of clinical relevance. RESULTS: The results showed no clinically relevant change in ACTH recovery for up to 4 h compared to standard conditions. For samples stored at room temperature for 4 h, a significant (p < .0001) relative mean change in ACTH concentrations of -4.3% was observed. CONCLUSION: The comparison between samples stored at room temperature for up to 4 h and standard conditions showed that ACTH samples do not require cooling until centrifugation, if a mean difference in ACTH concentration of -4.3%, between the individual results, can be accepted.

Salivary acetylcholinesterase activity is increased in Parkinson's disease: a potential marker of parasympathetic dysfunction.

Introduction. Decreased salivary flow and xerostomia are frequent findings in Parkinson's disease (PD), possibly caused by alterations in the parasympathetic tonus. Here we explore salivary acetylcholinesterase (AChE) activity as a potential biomarker in PD. Methods. We measured salivary flow, AChE activity, and total protein concentration in 30 PD patients and 49 healthy controls. We also performed exploratory correlation analyses with disease duration, motor symptom severity, autonomic complaints, and other nonmotor symptoms. Results. PD patients displayed significantly decreased salivary flow rate, significantly increased salivary AChE activity, and total protein concentration. Importantly, the AChE activity/total protein ratio was significantly increased in PD patients, suggesting that increased AChE activity cannot be explained solely by upconcentration of saliva. The Unified PD Rating Scale (UPDRS) score displayed significant correlation with total salivary protein (P = 0.002) and near-significant correlation with salivary flow (P = 0.07). Color vision test scores were also significantly correlated with AChE activity (P = 0.04) and total protein levels (P = 0.002). Conclusion. Salivary AChE activity is increased in PD patients compared to healthy controls. Future studies are needed to elucidate whether this parameter reflects the extent of neuronal damage and parasympathetic denervation in the salivary glands of PD patients.

Measurement of amino terminal propeptide of type III procollagen (PIIINP) employing the ADVIA Centaur platform. Validation, reference interval and comparison to UniQ RIA.

BACKGROUND: Recently, measurement of amino terminal propeptide of type III procollagen (PIIINP) was introduced as a part of the hepatic cirrhotic marker enhanced liver fibrosis™ test on the automated ADVIA Centaur(®) immunoassay platform (Siemens Healthcare Diagnostics Inc., Tarrytown, NY, USA). In this article, we show that the Centaur PIIINP may be used in place of the much more labor-intensive RIA method, and we present an age stratified reference interval. METHODS: We analyzed four control samples 20 times over a period of 5 days. Centaur PIIINP assay measurements were compared with the widely used UniQ PIIINP RIA assay (Orion Diagnostica, Espoo, Finland) using 55 patient samples (range=3.7-43.3 µg/L). Furthermore, we established a reference interval based on samples from 287 blood donors. RESULTS: In the concentration range 2.5-11.9 µg/L, the total imprecision was below 8%. Comparison with the UniQ PIIINP RIA assay yielded: Centaur PIIINP µg/L = 1.9 × (UniQ PIIINP RIA) + 0.6 µg/L, r2=0.94. The reference interval for the Centaur PIIINP assay showed no gender difference but was stratified by age [4.0-11.0 µg/L (18-40 years) and 3.5-9.5 µg/L (41-70 years)]. CONCLUSIONS: We conclude that the Centaur PIIINP assay is suitable for routine use with our newly defined reference interval. The results obtained by Centaur correlates well with those obtained by the previously employed RIA, though the absolute values are higher.

Analytical validation of the Roche 25-OH Vitamin D Total assay.

BACKGROUND: Vitamin D deficiency is considered a major health issue and therefore there is a need for reliable routine tests for measurement of the vitamin in blood samples. Here we present a validation of the recently released Roche 25-OH Vitamin D Total assay (Vitamin D Total). METHODS: We analyzed control materials (2 levels) and patient serum pools (3 levels) ranging from 34 to 123 nmol/L 84 times over a period of 21 days, and we analyzed five serum pools in 10 separate runs to verify the limit of quantification. We also analyzed 53 paired samples of serum and Li-heparin plasma. We evaluated the 25-OH Vitamin D Total assay in comparison to our in-house liquid chromatography tandem mass spectrometry (LC-MS/MS) method [194 patient samples without 25-hydroxy vitamin D(2) (25OHD(2)) and 23 patient samples containing 25OHD(2)]. RESULTS: At concentrations of 34 and 56 nmol/L within-run CVs were 4.8% and 1.9% and total CVs were 8.3% and 6.1%. We verified that the limit of quantification was 22.5 nmol/L, as stated by the manufacturer. No significant difference was observed between serum and plasma samples (Li-heparin). Comparison with LC-MS/MS using 194 samples containing 25OHD(3) only (no 25OHD(2)) showed Vitamin D Total nmol/L=1.07×(LC-MS/MS) nmol/L+4.7 nmol/L, whereas comparison of 25OHD(2) using 23 patient samples showed Vitamin D Total nmol/L=0.55×(LC-MS/MS) nmol/L-2.38 nmol/L (Demings regression). CONCLUSIONS: The Roche Vitamin D Total assay is judged suitable for measurement of 25OHD in serum and Li-heparin plasma. Results for 25OHD(3) are comparable to those obtained by LC-MS/MS, while results for 25OHD(2) are around half of those obtained by LC-MS/MS.