Pediatric reference intervals for serum folate and cobalamin based on a European population without exposure to folic acid fortification.

The aim of the present study was to define pediatric reference intervals for serum cobalamin and folate utilizing data generated from a population not exposed to food fortified with folic acid. Folate and cobalamin results analyzed by electrochemiluminescence immunoassay (Roche Cobas) were obtained from 2375 children (2 months to 17.99 years of age). The serum samples were collected between 2011 and 2015 as part of the LIFE (Leipzig Research Centre for Civilization Diseases) Child cohort study in Germany, where folic acid fortification of food is not mandated. These results were used to generate age- and gender-specific reference intervals presented as non-parametric 2.5 and 97.5 percentiles. Because of a subsequent restandardisation of the Roche folate assay in 2016, folate values were recalculated accordingly for adaptation to results obtained using the present calibration. In both genders, folate concentrations decreased continuously with age, whereas cobalamin concentrations peaked at five years of age and then declined. Teenage females had higher concentrations of cobalamin in the age group 12-17.99 years.

The complexity of kidney disease and diagnosing it - cystatin C, selective glomerular hypofiltration syndromes and proteome regulation.

Estimation of kidney function is often part of daily clinical practice, mostly done by using the endogenous glomerular filtration rate (GFR)-markers creatinine or cystatin C. A recommendation to use both markers in parallel in 2010 has resulted in new knowledge concerning the pathophysiology of kidney disorders by the identification of a new set of kidney disorders, selective glomerular hypofiltration syndromes. These syndromes, connected to strong increases in mortality and morbidity, are characterized by a selective reduction in the glomerular filtration of 5-30 kDa molecules, such as cystatin C, compared to the filtration of small molecules <1 kDa dominating the glomerular filtrate, for example water, urea and creatinine. At least two types of such disorders, shrunken or elongated pore syndrome, are possible according to the pore model for glomerular filtration. Selective glomerular hypofiltration syndromes are prevalent in investigated populations, and patients with these syndromes often display normal measured GFR or creatinine-based GFR-estimates. The syndromes are characterized by proteomic changes promoting the development of atherosclerosis, indicating antibodies and specific receptor-blocking substances as possible new treatment modalities. Presently, the KDIGO guidelines for diagnosing kidney disorders do not recommend cystatin C as a general marker of kidney function and will therefore not allow the identification of a considerable number of patients with selective glomerular hypofiltration syndromes. Furthermore, as cystatin C is uninfluenced by muscle mass, diet or variations in tubular secretion and cystatin C-based GFR-estimation equations do not require controversial race or sex terms, it is obvious that cystatin C should be a part of future KDIGO guidelines.

Interlaboratory variation for NT-proBNP among Swedish laboratories in an external quality program 2011-2021.

OBJECTIVES: NT-proBNP is frequently used for ruling out heart failure. Different cut-offs are used depending on the clinical context, e.g. an acute or chronic condition. Medical decision limits have been suggested at 125 and 300 ng/L or 400 ng/L in international guidelines. However, there is limited standardization between NT-proBNP methods and using the same blood sample might cause different treatment of patients. METHODS: Data from the external quality assessment program for NT-proBNP from Equalis, Sweden, were extracted for the period 2011-2021, and categorized according to manufacturer. Manufacturer median NT-proBNP values were compared to total median values. CV% was calculated for each manufacturer and in comparison to different levels of NT-proBNP. RESULTS: Roche was the most common method, and its median results were closest to the median consensus results. When looking at the total CV at NT-proBNP levels in the range of 0-500 ng/L, the total CV varied from 4 to 27%. During 2019-2021, Siemens (Immulite, Centaur, Atellica) yielded results 16-20% above the consensus median depending on sample level. Similarly, Abbott was 5-7% above, while Roche and Siemens Stratus were 1% respectively 6-10% below the consensus median. CONCLUSIONS: The introduction of new manufacturers and methods in 2017 have caused the agreement between manufacturers to decline. This highlights the need for a common calibrator and reference materials, particularly since medical decision limits in guidelines, e.g. European Society of Cardiology 2021, which are mostly based on Roche methods, do not take these method differences into account.

Lower creatinine concentration values and lower inter-laboratory variation among Swedish hospital laboratories in 2014 compared to 1996: results from the Equalis external quality assessment program.

Background Creatinine measurement for estimation of glomerular filtration rate (GFR) is a frequently used laboratory test. Differences in analytic creatinine methods have caused large inter-laboratory variation. International and national standardization efforts have been made in the last decade. Methods This study describes the results of the standardization efforts in Sweden by summarizing data for creatinine concentration in blood plasma in the Equalis quality assessment program during 1996-2014. Results Non-compensated Jaffe methods dominated in 1996-2001 (91 of 103 laboratories; 90%) and were then gradually replaced by either compensated Jaffe methods or enzymatic creatinine methods. In 2014 a majority of Swedish hospital laboratories (139 of 159; 87%) used enzymatic methods. The reported mean creatinine value by the Swedish laboratories was about 10 µmol/L higher than the isotope dilution mass spectrometry (IDMS) assured reference value in 2003, but consistent with the reference value from 2009 to 2014. The inter-laboratory CV was 7%-9% for creatinine values until 2007, and thereafter gradually decreased to about 4%-5% in 2014. Conclusions The introduction of enzymatic methods in Swedish laboratories has contributed to achieving a low inter-laboratory variation. Also, the reported values are lower for enzymatic methods compared to Jaffe methods, and the values obtained with enzymatic methods were consistent with IDMS certified values established at reference laboratories. Thus, many Swedish hospital laboratories reported 10 µmol/L lower, and more true, creatinine concentrations in 2012 than in 2003, which may cause bias in longitudinal studies.

Age- and sex-specific reference values for non-HDL cholesterol and remnant cholesterol derived from the Nordic Reference Interval Project (NORIP).

OBJECTIVES: Non-HDL-cholesterol (non-HDL-C) has been reported to be a better marker of cardiovascular risk than LDL-cholesterol (LDL-C) especially in individuals with high triglyceride values. Further, levels of remnant cholesterol have been suggested to in part explain residual risk not captured with LDL-C. The aim of the present study was to define reference values for non-HDL-C and remnant cholesterol based on data from the Nordic Reference Interval Project (NORIP). METHODS: We analyzed the test results for total cholesterol, HDL-cholesterol and triglycerides from 1392 healthy females and 1236 healthy males. Non-HDL-C was calculated as measured total cholesterol minus measured HDL-cholesterol. Remnant cholesterol was calculated using the Friedewald equation for LDL-C: measured total cholesterol minus measured HDL-cholesterol and minus calculated LDL-cholesterol. The 2.5th and 97.5th percentiles for these markers were calculated according to the International Federation of Clinical Chemistry guidelines on the statistical treatment of reference values. RESULTS: Age (18-<30, 30-49 and ≥50 years) and sex-specific reference intervals were calculated for non-HDL-cholesterol and remnant-cholesterol. Levels of non-HDL-C and remnant cholesterol differed between sex and age strata. CONCLUSIONS: Age- and sex-specific reference intervals should be used for the triglyceride rich lipid variables non-HDL-C and remnant cholesterol. Since these markers may add information on risk burden beyond LDL-C, our hope is that these reference intervals will aid the introduction of automatic reporting of non-HDL-C by hospital laboratories.

Dietary intake and biomarker status of folate in Swedish adults.

PURPOSE: National data on folate status are missing in Sweden, and regional data indicate folate insufficiency in up to more than 25% of the study populations. The objectives were to determine folate intake and status in the adult Swedish population as well as identifying dietary patterns associated with beneficial folate status. METHODS: Folate intake was estimated using a web-based 4-d food record in adults aged 18-80 years (n = 1797). Folate status was measured as erythrocyte (n = 282) and plasma folate concentrations (n = 294). Factor analysis was used to derive a dietary pattern associated with a higher folate status. RESULTS: Median folate intake was 246 µg/day (Q 1 = 196, Q 3 = 304, n = 1797) and for women of reproductive age 227 µg/day (Q 1 = 181, Q 3 = 282, n = 450). As dietary folate equivalents (DFE), median intake was 257 µg/day (Q 1 = 201, Q 3 = 323) and for women of reproductive age 239 µg/day (Q 1 = 185, Q 3 = 300). Low blood folate concentrations were found in 2% (erythrocyte concentrations <317 nmol/L) and 4% (plasma concentrations <6.8 nmol/L) of the participants, respectively. None of the women of reproductive age had erythrocyte folate concentrations associated with the lowest risk of neural tube defects. Dietary patterns associated with higher folate status were rich in vegetables, pulses and roots as well as cheese and alcoholic beverages, and low in meat. CONCLUSIONS: Prevalence of low erythrocyte folate concentrations was low in this population, and estimated dietary intakes are well above average requirement. However, to obtain a folate status optimal for prevention of neural tube defects major dietary changes are required and folic acid supplements recommended prior to conception.

Pediatric reference intervals for general clinical chemistry components - merging of studies from Denmark and Sweden.

BACKGROUND: Reference intervals are crucial tools aiding clinicians when making medical decisions. However, for children such values often are lacking or incomplete. The present study combines data from separate pediatric reference interval studies of Denmark and Sweden in order to increase sample size and to include also pre-school children who were lacking in the Danish study. METHODS: Results from two separate studies including 1988 healthy children and adolescents aged 6 months to 18 years of age were merged and recalculated. Eighteen general clinical chemistry components were measured on Abbott and Roche platforms. To facilitate commutability, the NFKK Reference Serum X was used. RESULTS: Age- and gender-specific pediatric reference intervals were defined by calculating 2.5 and 97.5 percentiles. CONCLUSION: The data generated are primarily applicable to a Nordic population, but could be used by any laboratory if validated for the local patient population.

Albumin adjustment of total calcium does not improve the estimation of calcium status.

BACKGROUND: There is a longstanding controversy as to whether plasma measurements of total calcium should be adjusted for albumin concentration, and if so which formulas are the most appropriate. METHODS: Ionised calcium, total calcium and albumin results, analysed at the same time at Uppsala University Hospital Laboratory between February 2005 and June 2013, were retrieved from a laboratory information system. The dataset included results from 20,003 patients. Total calcium was albumin-modified by a locally derived formula, based on 3106 patients from the dataset, and formulas from the literature. The agreement between the reference method ionised calcium and unadjusted total calcium and the seven different albumin-modifying calcium formulas, respectively, were compared with intra-class correlation coefficients (ICC). RESULTS: Total calcium showed substantial agreement to ionised calcium, ICC 0.85 (95% CI 0.84-0.86) for the whole validation cohort. Albumin-modified calcium by different formulas showed significantly less or equal agreement, however the locally determined formula performed better than formulas taken from the literature. Also, total calcium classified the patient as hypo-normo- or hypercalcemic right in 82% of the patients. The albumin-modified calcium did not classify patients significantly better except in the subgroup hypoalbuminemia (<30 g/L) where the local formula classified the patients slightly better than total calcium. CONCLUSIONS: Albumin modification of total calcium determinations is unlikely to add valuable information, and this practice should be abandoned. Ionised calcium should be used more frequently when aberrant results for total calcium are followed up, or in patients with known hypoalbuminemia.

Estimating reliable paediatric reference intervals in clinical chemistry and haematology.

UNLABELLED: Very few high-quality studies on paediatric reference intervals for general clinical chemistry and haematology analytes have been performed. Three recent prospective community-based projects utilising blood samples from healthy children in Sweden, Denmark and Canada have substantially improved the situation. CONCLUSION: The present review summarises current reference interval studies for common clinical chemistry and haematology analyses.

Inter-laboratory variation for urine albumin among laboratories in a Swedish external quality assessment scheme 2005-2023.

INTRODUCTION: Increased albuminuria is associated with elevated mortality. Urine albumin (U-ALB) above 20 mg/L or albumin-to-creatinine ratio (U-ACR) of 3 g/mol are indicative of moderately increased albuminuria. Due to limited standardization among U-ALB methods, diagnosis of increased albuminuria might prove difficult. MATERIALS AND METHODS: Data from Equalis's external quality assessment scheme for low U-ALB levels during 2005-2023 were categorized according to manufacturer and divided into central laboratory (CLAB) and point-of-care testing (POCT) methods. Manufacturer median values were compared to total group mean consensus values and manufacturer CV% was compared at different U-ALB levels. RESULTS: CLAB was generally closer to consensus values and had lower CV% than POCT at U-ALB levels around 20 mg/L. For CLAB, Roche methods were approximately equal to consensus U-ALB, Abbott 4 % above, and Siemens 5 % below. For POCT, HemoCue was 1 % below, Siemens 7 % above, and Abbott 8 % below. For U-Creatinine, all manufacturers generally had a good agreement differing on average by 1-4 % from consensus. CONCLUSIONS: Although U-ALB methods generally meet The National Kidney Disease Education Program (NKDEP) recommendations of method bias less than 13 % and imprecision less than 30 %, differences among manufacturers have increased over the last years, with 2023 showing the largest differences between methods. This highlights the need for guidelines for albuminuria and ACR to take method differences into consideration, but also for implementation of suitable urine reference materials.

Population-based pediatric reference intervals for hematology, iron and transferrin.

Reference intervals are crucial decision-making tools aiding clinicians in differentiating between healthy and diseased populations. However, for children such values often are lacking or incomplete. Blood samples were obtained from 689 healthy children, aged 6 months to 18 years, recruited in day care centers and schools. Hematology and anemia analytes were measured on the Siemens Advia 2120 and Abbott Architect ci8200 platforms (hemoglobin, erythrocyte volume fraction [EVF], erythrocytes, mean corpuscular volume [MCV], mean corpuscular hemoglobin [MCH], mean corpuscular hemoglobin concentration [MCHC], reticulocytes, leukocytes, lymphocytes, monocytes, neutrophils, eosinophils, basophils, platelets, iron, transferrin, transferrin saturation). Age- and gender-specific pediatric reference intervals were defined by calculating 2.5th and 97.5th percentiles. The data generated is primarily applicable to a Caucasian population, but could be used by any laboratory if verified for the local patient population.

Population-based pediatric reference intervals for HbA1c, bilirubin, albumin, CRP, myoglobin and serum enzymes.

BACKGROUND: Many previous studies on reference intervals are hampered by the inclusion of only hospital-based populations of children and adolescents. METHODS: This study included 694 children, evenly distributed from 6 months to 18 years of age. They were recruited as volunteers at child care units and schools. All subjects were apparently healthy. A questionnaire on diseases and medications was filled out by parents and by the older children. RESULTS: Alanine aminotransferase (ALT), albumin, aspartate aminotransferase (AST), bilirubin, conjugated bilirubin, C-reactive protein (CRP), creatine kinase (CK), Gamma-glutamyltransferase (GGT), HbA1c (mono S and IFCC calibrations), lactate dehydrogenase (LD), myoglobin and panceratic amylase were analyzed on Abbott Architect ci8200, and for HbA1c on Tosoh G7 and a mono S-system. Age- and gender-related 2.5th and 97.5th percentiles were estimated. For some analytes the differences to comparable studies were substantial. CONCLUSION: The study gives age- and gender-specific pediatric reference intervals, measured with modern methods for a number of important analytes. The results emphasize the importance to evaluate pediatric reference intervals in different populations and ethnic groups including only healthy subjects.

Diurnal variability of total calcium during normal sleep and after an acute shift of sleep.

BACKGROUND: Serum total calcium is becoming a widely used test when screening for hyperparathyroidism (HPT) and other causes of hypercalcemia, even if serum calcium is tightly regulated in the body it is unclear whether the reference values are correct for tests taken at different times of the day or for individuals with altered sleep patterns. Thus, the aim was to investigate how timing of testing and sleep affects serum calcium. METHODS: The diurnal variation of total calcium in serum during night-time and day-time conditions was studied in seven healthy volunteers. Serum samples for calcium measurements were collected every hour (48 samples per individual) to evaluate the effect of sampling times, sleep and food intake on the test results. RESULTS: The median intra-individual coefficients of variations for calcium were 3.3% during night-time sleep and 2.8% during day-time sleep conditions. There was a clear diurnal variation in serum calcium, with a trough at 08.00 h in the morning after night-time sleep and a difference of approximately 0.07 mmol/L between trough and peak. Calcium was lower around the end of the sleep periods, for both night-time and day-time sleep. Food intake did not affect calcium concentrations. CONCLUSIONS: Evaluation of serum calcium results should take diurnal variation into account and allow slightly higher calcium values in the afternoon in comparison with samples collected in the morning.

Population-based pediatric reference intervals for general clinical chemistry analytes on the Abbott Architect ci8200 instrument.

BACKGROUND: Reference intervals are crucial decision-making tools aiding clinicians in differentiating between healthy and diseased populations. However, for children such values often are lacking or incomplete. METHODS: Blood samples were obtained from 692 healthy children, aged 6 months to 18 years, recruited in daycare centers and schools. Twelve common general clinical chemistry analytes were measured on the Abbott Architect ci8200 platform; sodium, potassium, chloride, calcium, albumin-adjusted calcium, phosphate, magnesium, creatinine (Jaffe and enzymatic), cystatin C, urea and uric acid. RESULTS: Age- and gender specific pediatric reference intervals were defined by calculating the 2.5th and 97.5th percentiles. CONCLUSIONS: The data generated is primarily applicable to a Caucasian population when using the Abbott Architect platform, but could be used by any laboratory if validated for the local patient population.

Reference intervals on the Abbot Architect for serum thyroid hormones, lipids and prolactin in healthy children in a population-based study.

Pediatric reference intervals for thyroid hormones, prolactin and lipids are of high clinical importance as deviations might indicate diseases with serious consequences. In general, previous reference intervals are hampered by the inclusion of only hospital-based populations of children and adolescents. The study included 694 children, evenly distributed from 6 months to 18 years of age. They were recruited as volunteers at child care units and schools. All subjects were apparently healthy and a questionnaire on diseases and medications was filled out by parents and by the older children. TSH, free T4, free T3, total cholesterol, LDL, HDL, triglycerides and prolactin were analyzed on Abbott Architect ci8200. Age- and gender-related 2.5 and 97.5 percentiles were estimated. The thyroid hormone levels were similar to previous data for the Abbott Architect platform, but exhibited differences from studies performed with other methods. Prolactin displayed wide reference ranges, but relatively small age-related changes, and a marginal difference between sexes during adolescence. Reference intervals for lipids in the different age groups are known to vary geographically. Levels of LDL and total cholesterol were higher than those reported for children in Canada, but lower than those reported for children in China. The study gives age- and gender- specific pediatric reference intervals, measured with modern methods for a number of important analytes. The results presented here differ from previously recommended reference intervals. In many earlier studies, retrospective hospital-based reference intervals, which may include various sub-groups have been presented. By non-hospital studies it is possible to avoid some of these biases.

Hemolysis interference in 10 coagulation assays on an instrument with viscosity-based, chromogenic, and turbidimetric clot detection.

INTRODUCTION: Hemolysate in plasma samples from patients may cause misleading results in coagulation assays. Even though modern coagulation instruments often are equipped with modules that can detect hemolysis, icterus, and lipemia (HIL), studies that report the influence of these interferences are still limited. The present paper focuses on the influence of hemolysis on 10 coagulation assays. METHODS: Artificial hemolysis was created by freezing/thawing, and the hemolysates generated were added to pools of patient plasma. Pathological and normal levels were pooled separately. These spiked samples were analyzed on a STA R Max 2 instrument. The coagulation assays evaluated utilize clot, chromogenic, or immunoturbidimetric detection. RESULTS: Four of the evaluated assays were not influenced by hemolysis: fibrinogen, von Willebrand factor antigen, activated partial thromboplastin time, and factor VIII. Interestingly, normal and slightly elevated prothrombin time (INR < 2.0) was insensitive to hemolysis, whereas samples with a high INR (≥2.0) exhibited falsely high readings. The assays for antithrombin and fibrin D-dimer displayed an intermediate sensitivity to hemolysis. The most sensitive assay turned out to be anti-Xa, followed by protein C and protein S. For the anti-Xa assay, the results are decreased by 10% already at 0.5 g/L hemoglobin. CONCLUSION: The present study shows that hemolysis affects several of commonly used coagulation assays. Since the sensitivity for hemolysis is dependent on the brand of the assay as well as the instrument and principle of measurement, it is necessary to evaluate the influence of each specific combination.

Vitamin D status in children and adults in Sweden: dietary intake and 25-hydroxyvitamin D concentrations in children aged 10-12 years and adults aged 18-80 years.

The study aimed to estimate vitamin D intake and plasma/serum 25-hydroxyvitamin D (25(OH)D) concentrations, investigate determinants of 25(OH)D concentrations and compare two 25(OH)D assays. We conducted two nationwide cross-sectional studies in Sweden with 206 school children aged 10-12 years and 1797 adults aged 18-80 years (n 268 provided blood samples). A web-based dietary record was used to assess dietary intake. Plasma/serum 25(OH)D was analysed by liquid chromatography-mass spectrometry (LC-MS) and immunoassay in adults and LC-MS/MS in children. Most participants reported a vitamin D intake below the average requirement (AR), 16 % of children and 33 % of adults met the AR (7⋅5 µg). In adults, plasma 25(OH)D below 30 and 50 nmol/l were found in 1 and 18 % of participants during the summer period and in 9 and 40 % of participants during the winter period, respectively. In children, serum 25(OH)D below 30 and 50 nmol/l were found in 5 and 42 % of participants (samples collected March-May), respectively. Higher 25(OH)D concentrations were associated with the summer season, vacations in sunny locations (adults), and dietary intake of vitamin D and use of vitamin D supplements, while lower concentrations were associated with a higher BMI and an origin outside of Europe. Concentrations of 25(OH)D were lower using the immunoassay than with the LC-MS assay, but associations with dietary factors and seasonal variability were similar. In conclusion, vitamin D intake was lower than the AR, especially in children. The 25(OH)D concentrations were low in many participants, but few participants had a concentration below 30 nmol/l.

Fecal markers of inflammation used as surrogate markers for treatment outcome in relapsing inflammatory bowel disease.

AIM: To evaluate fecal calprotectin (FC) as a surrogate marker of treatment outcome of relapse of inflammatory bowel disease (IBD) and, to compare FC with fecal myeloperoxidase (MPO) and fecal eosinophil protein X (EPX). METHODS: Thirty eight patients with IBD, comprising of 27 with ulcerative colitis (UC) and 11 with Crohn's disease (CD) were investigated before treatment (inclusion), and after 4 and 8 wk of treatment. Treatment outcomes were evaluated by clinical features of disease activity and endoscopy in UC patients, and disease activity in CD patients. In addition, fecal samples were analyzed for FC by enzyme-linked immunosorbent assay (ELISA), and for MPO and EPX with radioimmunoassay (RIA). RESULTS: At inclusion 37 of 38 (97%) patients had elevated FC levels (> 94.7 microg/g). At the end of the study, 31 of 38 (82%) patients fulfilled predefined criteria of a complete response [UC 21/27 (78%); CD 10/11 (91%)]. Overall, a normalised FC level at the end of the study predicted a complete response in 100% patients, whereas elevated FC level predicted incomplete response in 30%. Normalised MPO or EPX levels predicted a complete response in 100% and 90% of the patients, respectively. However, elevated MPO or EPX levels predicted incomplete response in 23% and 22%, respectively. CONCLUSION: A normalised FC level has the potential to be used as a surrogate marker for successful treatment outcome in IBD patients. However, patients with persistent elevation of FC levels need further evaluation. FC and MPO provide superior discrimination than EPX in IBD treatment outcome.