Reference intervals for holotranscobalamin and total vitamin B12 in 6-12-year-old children in Norway: the Health Oriented Pedagogical Project (HOPP)

Vitamin B12 (B12) is essential for DNA synthesis in all cells and for the development and maintenance of a healthy nervous system. B12 is transported in the circulation bound to two carrier proteins, haptocorrin and transcobalamin, measured as the biomarkers total B12 and holotranscobalamin (holoTC). The latter measures the fraction of cobalamin available for tissue uptake and is considered to have a better sensitivity and specificity for diagnosing vitamin deficiency. The concentration of both carrier proteins depends on age, but data on paediatric reference values for holoTC are still sparse. Blood samples were obtained from 1320 healthy school children, mainly Caucasians (age 6-12 years old) in three different municipalities in Norway. The holoTC and total B12 levels were determined by chemiluminescent microparticle immunoassay on the Architect 2000 analyser. Age specific paediatric reference intervals (RIs) were estimated by calculating the 2.5 and 97.5 percentiles by the nonparametric method with corresponding 90% confidence intervals, according to the Clinical and Laboratory Standards Institute C28-A3C guidelines. The 95% RIs for total B12 were 295-1066 pmol/L for children 6-8 years old, and 249-879 pmol/L for children 9-12 years old. Reference intervals for holoTC were ≥56 pmol/L for children 6-8 years old, and ≥37 pmol/L for children 9-12 years old. Age specific RIs will aid clinicians in interpretation of cobalamin results in children aged 6-12 years old.

Neonatal Thyroid-Stimulating Hormone Reference Intervals in Multi-Ethnics Population

(1) Background: This study is designed to establish thyroid-stimulating hormone (TSH) reference intervals tailored to different neonatal age groups and Indonesian local populations. (2) Methods: Dried blood spot neonatal TSH values, from 1 January 2022 to 31 December 2023, were used to establish the neonatal TSH reference intervals partitioned by sex, gestational age, and ethnic group at different neonatal ages. (3) Results: A significant difference in the reference intervals value was observed in sex, gestational ages, and parental ethnicity groups in different neonatal age subgroups (p < 0.05). Male reference intervals were significantly higher than those of females at all neonatal ages. Late and post-term gestational age categories reference intervals were higher than early and full-term. Among the ethnic groups, Madurese had a higher upper limit TSH reference interval. (4) Conclusions: Our neonatal TSH reference intervals were needed to provide a reference adapted to the local population of Indonesia.

Multidisciplinary approach to redefining thyroid hormone reference intervals with big data analysis

OBJECTIVES

This study aimed to employ big data analysis to harmonize reference intervals (RI) for thyroid function tests, with refinement to the TSH upper reference limit, and to optimize the TSH reflex algorithm to improve clinical management and test utilization.

DESIGN & METHODS

TSH, free T4, and free T3 results tested in Alberta, Canada, on Roche Cobas and Siemens Atellica were extracted from the laboratory information system (N = 1,144,155 for TSH, N = 183,354 for free T4 and N = 92,632 for free T3). Results from specialists, inpatients, or repeat testing, as well as from positive thyroid disease, autoimmune disease, and pregnancy biomarkers were excluded. RIs were derived using statistical models (Bhattacharya, refineR, and simple non-parametric) followed by endocrinology and laboratory review.

RESULTS

The TSH RIs for 0 to 7 days, 8 days to 1 year, and ≥1 year were 1.23 to 25.0 mIU/L, 1.00 to 6.80 mIU/L and 0.20 to 6.50 mIU/L, respectively. The free T4 RIs for 0 to 14 days, 15 to 29 days, and ≥30 days were 13.5 to 50.0 pmol/L, 8.7 to 32.5 pmol/L, and 10.0 to 25.0 pmol/L, respectively. An updated TSH reflex algorithm was developed based on the optimized TSH and free T4 RIs, with free T4 reflexed only at a TSH of <0.1 mIU/L.

CONCLUSIONS

The collaboration of a multidisciplinary team and the utilization of big data analysis led to the enhancement of thyroid function RIs, specifically resulting in the widening of the upper TSH reference limit to 6.50. Application of these optimized RIs with the TSH reflex algorithm will serve as a guide for improvement in interpretation of thyroid function tests.

Age-Specific Reference Intervals for Thyroid-Stimulating Hormones and Free Thyroxine to Optimize Diagnosis of Thyroid Disease

Background: Thyroid-stimulating hormone (TSH) and subsequent free thyroxine (FT4) concentrations outside the reference interval (RI) are used to diagnose thyroid diseases. Most laboratories do not provide age-specific RIs for TSH and FT4 beyond childhood, although TSH concentrations vary with age. Therefore, we aimed to establish TSH and FT4 age-specific RIs throughout life and aimed to determine whether using these RIs would result in reclassification of thyroid disease diagnoses in adults. Methods: This multicenter retrospective cross-sectional study used big data to determine indirect RIs for TSH and FT4. These RIs were determined by TMC and refineR-analysis, respectively, using four different immunoassay platforms (Roche, Abbott, Siemens, and Beckman Coulter). Retrospective data (2008-2022) from 13 Dutch laboratories for general practitioners and local hospitals were used. RIs were evaluated per manufacturer. Age groups were established from 2 to 20 years by 2-year categories and decade categories between 20 and 100 years. Results: We included totally 7.6 million TSH and 2.2 million FT4 requests. TSH upper reference limits (URLs) and FT4 lower reference limits were higher in early childhood and decreased toward adulthood. In adulthood, TSH URLs increased from 60 years in men, and from 50 years in women, while FT4 URLs increased from 70 years onward. Using adult age-specific RIs resulted in a decrease in diagnoses of subclinical and overt hypothyroidism in women above 50 and men above 60 years in our Roche dataset. Conclusion: This study stressed the known importance of using age-specific RIs for TSH and FT4 in children. This study also showed the clinical relevance of using age-specific RIs for TSH in adulthood to reduce diagnoses of subclinical hypothyroidism in older persons. Therefore, implementation of adult TSH age-specific RIs should be strongly considered. Data are less uniform regarding FT4 age-specific RIs and more research should be performed before implementing these in clinical practice.

Diagnosis and Treatment of Iron Deficiency and Iron Deficiency Anemia in Children and Adolescents: Recommendations of the Polish Pediatric Society, the Polish Society of Pediatric Oncology and Hematology, the Polish Society of Neonatology, and the Polish Society of Family Medicine

Background/Objectives. Iron deficiency is one of the most common nutritional deficiencies worldwide and is the leading cause of anemia in the pediatric population (microcytic, hypochromic anemia due to iron deficiency). Moreover, untreated iron deficiency can lead to various systemic consequences and can disrupt the child's development. Methods/Results. Therefore, a team of experts from the Polish Pediatric Society, the Polish Society of Pediatric Oncology and Hematology, the Polish Neonatology Society, and the Polish Society of Family Medicine, based on a review of the current literature, their own clinical experience, and critical discussion, has developed updated guidelines for the diagnosis, prevention, and treatment of iron deficiency in children from birth to 18 years of age. These recommendations apply to the general population and do not take into account the specifics of individual conditions and diseases.

The Benefit of Detecting Reduced Intracellular B12 Activity through Newborn Screening Remains Unclear

Vitamin B12 (B12) deficiency (B12D) can have detrimental effects on early growth and development. The Austrian newborn screening (NBS) program targets inborn errors of cobalamin metabolism and also detects B12D. Of 59 included neonates with B12D suspected by NBS, B12D was not further investigated in 16 (27%) retrospectively identified cases, not confirmed in 28 (48%), and confirmed in 15 (25%) cases. NBS and recall biomarkers were recorded. Age at sampling of the dried blood spots for NBS and the 1st-tier methionine/phenylalanine ratio were the strongest parameters to predict B12D (67.4% correct allocations). No differences between cases with confirmed, unconfirmed, or unknown B12D or differences to norms were observed for growth and psychomotor development (Vineland III scales, phone interviews with parents of children between months 10 and 14 of life). B12 intake was below recommendations in most mothers. NBS can detect reduced intracellular B12 activity. No advantage of NBS detection and treatment regarding infant cognitive development or growth could be proven. Since conspicuous NBS findings cannot be ignored, and to prevent exposing newborns to invasive diagnostics, assessment of maternal B12 status during pregnancy seems advisable.

Analysis of Serum Free Thyroxine Concentrations in Healthy Term Neonates Underlines Need for Local and Laboratory-Specific Reference Interval: A Systematic Review and Meta-Analysis of Individual Participant Data

Background: Initial evaluation of the hypothalamus-pituitary-thyroid axis is done by measuring serum free thyroxine (fT4) and thyrotropin concentrations. For correct interpretation of these measurements, reliable age-specific reference intervals (RIs) are fundamental. Since neonatal fT4 RIs conforming to the Clinical and Laboratory Standards Institute guidelines are not available for all assays, we set out to create literature-based uniform age-specific neonatal fT4 RIs that may be used for every assay. Methods: For meta-analysis of individual participant fT4 concentrations, we systematically searched MEDLINE and Embase (search date December 6, 2023; PROSPERO registration CRD42016041871). We searched for studies reporting fT4 concentrations in healthy term newborns aged 2-27 days, born to mothers without thyroid disease in iodine-sufficient regions. Authors were invited to supply data. Due to standardization differences between assays, data could not be combined for meta-analysis directly, and we attempted to normalize the data using two distinct methods. Results: We obtained 4206 fT4 concentrations from 20 studies that used 13 different assays from 6 manufacturers. First, we set out to normalize fT4 data using the mean and standard deviation of (assay-specific) adult RIs. fT4 concentrations were transformed into Z-scores, assuming a normal distribution. Using a linear mixed-effects model (LMM), we still found a significant difference between fT4 concentration across studies (p < 0.001), after this normalization. As a second approach, we normalized the fT4 concentrations using data from a method/assay comparison study. We used the relationship between the Cobas assay and the other assays as a reference point to convert all values to Cobas values. However, this method also failed to produce consistent results, with significant differences between the normalized data (LMM p < 0.001). Conclusions: We conclude that our attempts at normalizing fT4 assay results were unsuccessful. Confounders related to our unsuccessful analysis may be assay related and/or biological. These findings have significant implications for patient care, since relying on RIs from literature may result in erroneous interpretation of results. Therefore, we strongly recommend to establish local RIs for accurate interpretation of serum fT4 concentrations in neonates.

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.

Methodological considerations in determining sex steroids in children: comparison of conventional immunoassays with liquid chromatography-tandem mass spectrometry

OBJECTIVES

In laboratory medicine, external quality assessment (EQA) schemes have become versatile tools for detecting analytical flaws. However, EQA schemes are lacking for pediatric sex steroid levels. We aimed to investigate the suitability of different estradiol and testosterone immunoassays in a pediatric setting in comparison with clinical liquid chromatography-tandem mass spectrometry (LC-MS/MS) assays.

METHODS

The study was conducted by staff and the advisory group on endocrinology at Equalis, the Swedish provider of EQA schemes for laboratory medicine. The test material consisted of five pooled serum samples from children who were either prepubertal or in puberty. Clinical laboratories enrolled in Equalis EQA schemes for estradiol and testosterone were invited to participate, as were clinical laboratories using LC-MS/MS-assays. Samples were analyzed by either routine immunoassays (n=18) or in-house LC-MS/MS assays (n=3).

RESULTS

For estradiol, LC-MS/MS assays showed a high degree of conformity with interlaboratory coefficients of variation (CV) below 24.2 %. Reported levels were between 4.9 ± 1.2 and 33.9 ± 1.6 pmol/L (group mean ± standard deviation). The direct immunoassays had lower precision; their CVs were up to 81.4 %. Reported concentrations were between 25.3 ± 18.1 and 45.7 ± 19.4 pmol/L, an overestimation compared to LC-MS/MS. Testosterone LC-MS/MS also showed a high degree of conformity, CVs were below 13.4 %, and reported concentrations were from 0.06 ± 0.00 to 1.00 ± 0.11 nmol/L. The direct immunoassays had a larger discrepancy between results; CVs were up to 95.8 %. Concentrations were between 0.12 ± 0.11 and 0.85 ± 0.23 nmol/L.

CONCLUSIONS

For the safe diagnosis and determination of sex steroids in children, analysis with mass spectrometry-based methods is recommended.

Age-specific Reference Intervals of Abbott Intact PTH-Potential Impacts on Clinical Care

Background

PTH assays are not standardized; therefore, method-specific PTH reference intervals are required for interpretation of results. PTH increases with age in adults but age-related reference intervals for the Abbott intact PTH (iPTH) assay are not available.

Methods

Deidentified serum PTH results from September 2015 to November 2022 were retrieved from the laboratory information system of a laboratory serving a cosmopolitan population in central-west England for individuals aged 18 years and older if the estimated glomerular filtration rate was ≥60 mL/min, serum 25-hydroxyvitamin D was >50 nmol/L, and serum albumin-adjusted calcium and serum phosphate were within reference intervals. Age-specific reference intervals for Abbott iPTH were derived by an indirect method using the refineR algorithm.

Results

PTH increased with age and correlated with age when controlled for 25-hydroxyvitamin D, estimated glomerular filtration rate, and adjusted calcium (r = 0.093, P < .001). The iPTH age-specific reference intervals for 4 age partitions of 18 to 45 years, 46 to 60 years, 61 to 80 years, and 81 to 95 years were 1.6 to 8.6 pmol/L, 1.8 to 9.5 pmol/L, 2.0 to 11.3 pmol/L, and 2.3 to 12.3 pmol/L, respectively. PTH was higher in women compared with men (P < .001). Sex-specific age-related reference intervals could not be derived because of the limited sample size.

Conclusion

Age-specific Abbott iPTH reference intervals were derived. Application of age-specific reference intervals will impact the diagnosis and management of normocalcemic hyperparathyroidism, based on current definitions, and secondary hyperparathyroidism. Additional studies are required to clarify the effect of sex and ethnicity on PTH.

Reference Intervals for Thyroid Hormones and Thyroid Volume in Children Aged 7 ~ 13 Years from Iodine-Sufficient Areas in Tianjin, China

Reference intervals (RIs) for serum thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) suitable for local children are urgently needed in northern China. The reference interval for thyroid volume (Tvol) in Chinese children also differed greatly from that recommended by the WHO. This study aimed to establish TSH, FT3, FT4, and Tvol RIs suitable for children in northern China. A total of 1070 children aged 7 ~ 13 were recruited from iodine nutrition-sufficient areas in Tianjin, China, from 2016 to 2021. Four hundred fifty-eight children aged 7 ~ 13 years, and 815 children aged 8 ~ 10 years were eventually included to study RIs for the thyroid hormones and Tvol. RIs for thyroid hormones were established in accordance with the Clinical Laboratory Standards Institute (CLSI) document C28-A3 guidelines. Quantile regression was used to analyze the influencing factors of Tvol. RIs for TSH, FT3, and FT4 were 1.23 (1.14 ~ 1.32) to 6.18 (5.92 ~ 7.26) mIU/L, 5.43 (5.29 ~ 5.52) to 7.89 (7.66 ~ 7.98) pmol/L, and 13.09 (12.85 ~ 13.73) to 22.22 (21.61 ~ 22.51) pmol/L. There was no need to establish RIs by age and gender. Our RIs could increase the prevalence of subclinical hyperthyroidism (P < 0.001) and reduce the prevalence of subclinical hypothyroidism (P < 0.001). Body surface area (BSA) and age are correlated with the 97th percentile of Tvol (both P < 0.001). Our reference interval could increase the goiter rate in children from 2.97 to 4.96% (P = 0.007). The thyroid hormones' reference intervals suitable for local children should be established. In addition, BSA and age should be considered when establishing Tvol reference interval.

Biochemical, Nutritional, and Clinical Parameters of Vitamin B12 Deficiency in Infants: A Systematic Review and Analysis of 292 Cases Published between 1962 and 2022

Pooled data from published reports on infants with clinically diagnosed vitamin B12 (B12) deficiency were analyzed with the purpose of describing the presentation, diagnostic approaches, and risk factors for the condition to inform prevention strategies. An electronic (PubMed database) and manual literature search following the PRISMA approach was conducted (preregistration with the Open Science Framework, accessed on 15 February 2023). Data were described and analyzed using correlation analyses, Chi-square tests, ANOVAs, and regression analyses, and 102 publications (292 cases) were analyzed. The mean age at first symptoms (anemia, various neurological symptoms) was four months; the mean time to diagnosis was 2.6 months. Maternal B12 at diagnosis, exclusive breastfeeding, and a maternal diet low in B12 predicted infant B12, methylmalonic acid, and total homocysteine. Infant B12 deficiency is still not easily diagnosed. Methylmalonic acid and total homocysteine are useful diagnostic parameters in addition to B12 levels. Since maternal B12 status predicts infant B12 status, it would probably be advantageous to target women in early pregnancy or even preconceptionally to prevent infant B12 deficiency, rather than to rely on newborn screening that often does not reliably identify high-risk children.

Pediatric reference interval verification for 16 biochemical markers on the Alinity ci system in the CALIPER cohort of healthy children and adolescents

OBJECTIVES

Special chemistry parameters are useful in the diagnosis and management of inherited disorders, liver disease, and immunopathology. Evidence-based pediatric reference intervals (RIs) are required for appropriate clinical decision-making and need to be verified as new assays are developed. This study aimed to evaluate the applicability of pediatric RIs established for biochemical markers on the ARCHITECT for use on newer Alinity assays.

METHODS

An initial method validation was completed for 16 assays, including precision, linearity, and method comparison. Sera collected from approximately 100 healthy children and adolescents as part of the Canadian Laboratory Initiative on Pediatric Reference Intervals (CALIPER) were also analyzed on the Alinity c system. Percentage of results within established ARCHITECT RIs were calculated and considered verified if ≥90 % fell within established limits. New RIs were established for three electrolytes, glucose, and lactate wherein no data were previously reported.

RESULTS

Of the 11 assays for which CALIPER pediatric RIs were previously established on ARCHITECT assays, 10 met the verification criteria. Alpha-1-antitrypsin did not meet verification criterion and a new RI was established. For the other 5 assays, de novo RIs were derived following analysis of 139-168 samples from healthy children and adolescents. None required age- and sex-partitioning.

CONCLUSIONS

Herein, pediatric RIs were verified or established for 16 chemistry markers in the CALIPER cohort on Alinity assays. Findings support excellent concordance between ARCHITECT and Alinity assays with one exception (alpha-1-antitrypsin) as well as robustness of age- and sex-specific patterns originally reported by CALIPER in healthy Canadian children and adolescents.

Reference intervals for thyroid biomarkers to enhance the assessment of thyroid status in childhood and adolescence

OBJECTIVES

The determination of assay-dependent upper and lower reference limits (URL, LRL) of free triiodothyronine (FT3), free thyroxine (FT4), and thyroid stimulating hormone (TSH) during childhood and adolescence, is challenging.

METHODS

Thyroid hormones were measured via the Abbott Alinity system in 502 euthyroid children partitioned in the following age groups: ≤2, 2.1-10, and 10.1-18 years. The 97.5th and 2.5th percentiles (URL and LRL) were derived according to CLSI EP28- A3c guidelines. Quantile regression models were used to assess: (a) 90% confidence intervals of the URL and LRL, (b) the effect of age on URL and LRL within each age class and on overall age range, (c) the difference between the URLs and LRLs estimated for each age partition with an estimate of the confidence interval divided by the reference interval being derived (CI/RI).

RESULTS

The CI/RI for the LRLs are smaller as compared to the URLs, except for FT4 for the 2.1-10 years age group. Considering the CI/RI and the overlap between CIs across the three age groups, one single LRL might be considered for TSH, FT3 and FT4 between 0 and 18 years. However, for the URL, there was a noticeable decrease in the URL over the 3 age groups for all three biomarkers, with there being no overlap in CIs for the URL between the ≤2 vs. the 10.1-19 years age groups.

CONCLUSIONS

A common LRL for TSH, FT4 and FT3 for patients aged ≤18 years may be utilized when these biomarkers are measured with the Alinity system. For the URLs the use of age-specific URLs for these biomarkers is recommended.

Reference intervals for serum TSH concentrations of healthy children from the Central Region of Brazil

Objective

The objective of this study was to determine the serum thyroid-stimulating hormone (TSH) concentration reference intervals (RIs) of healthy children aged 1 to 10 years of both sexes, living in the Central Region of Brazil.

Subjects and methods

1,735 children [869 (50.1%) female; 866 (49.9%) male] enrolled in the morning shift of 47 pre- and 83 public elementary schools in the municipality of Cuiabá, Mato Grosso, were studied by gathering anthropometric and social data and their medical history. A blood sample was collected from each child to determine the TSH concentration using the electrochemiluminescence method on a Cobas® 6000 modular analyzer (Analyzer series, Roche Diagnostics).

Results

The RIs were determined using the 2.5 and 97.5 percentile and the mean ± 2 standard deviations methods. After identifying the homoscedastic groups by age and sex, outliers higher or lower than three standard deviations were excluded. The distribution of serum TSH concentrations showed no significant age or sex differences. Based on the percentile method, TSH RI ranged from 0.93 to 5.86 μIU/mL. Based on the mean ± 2 standard deviations, TSH RI ranged from 0.30 to 5.29 μIU/mL.

Conclusion

The normal serum TSH concentration of the Brazilian children evaluated in this study differ from those of populations from other countries. Other regional population studies may validate the RIs found in this study and enable its safer use in pediatric clinical practice.

Neonatal reference intervals for thyroid stimulating hormone and free thyroxine assayed on a Siemens Atellica® IM analyzer: a cross sectional study

BACKGROUND

Deriving population specific reference intervals (RIs) or at the very least verifying any RI before adoption is good laboratory practice. Siemens has provided RIs for thyroid stimulating hormone (TSH) and free thyroxine (FT4) determined on their Atellica® IM analyzer for all age groups except the neonatal age group which provides a challenge for laboratories that intend to use it to screen for congenital hypothyroidism (CH) and other thyroid disorders in neonates. We set out to determine RIs for TSH and FT4 using data obtained from neonates undergoing routine screening for CH at the Aga Khan University Hospital, Nairobi, Kenya.

METHODOLOGY

TSH and FT4 data for neonates aged 30 days and below were extracted from the hospital management information system for the period March 2020 to June 2021. A single episode of testing for the same neonate was included provided both TSH and FT4 were done on the same sample. RI determination was performed using a non-parametric approach.

RESULTS

A total of 1243 testing episodes from 1218 neonates had both TSH and FT4 results. A single set of test results from each neonate was used to derive RIs. Both TSH and FT4 declined with increase in age with a more marked decline seen in the first 7 days of life. There was a positive correlation between logFT4 and logTSH (r_s (1216) = 0.189, p = < 0.001). We derived TSH RIs for the age groups 2-4 days (0.403-7.942 µIU/mL) and 5-7 days (0.418-6.319 µIU/mL), and sex specific RIs for males (0.609-7.557 µIU/mL) and females (0.420-6.189 µIU/mL) aged 8-30 days. For FT4, separate RIs were derived for the age groups 2-4 days (1.19-2.59 ng/dL), 5-7 days (1.21-2.29 ng/dL) and 8-30 days (1.02-2.01 ng/dL).

CONCLUSION

Our neonatal RIs for TSH and FT4 are different from those published or recommended by Siemens. The RIs will serve as a guide for the interpretation of thyroid function tests in neonates from sub-Saharan Africa where routine screening for congenital hypothyroidism using serum samples is done on the Siemens Atellica® IM analyzer.

Mineral Metabolism in Children: Interrelation between Vitamin D and FGF23

Fibroblast growth factor 23 (FGF23) was identified at the turn of the century as the long-sought circulating phosphatonin in human pathology. Since then, several clinical and experimental studies have investigated the metabolism of FGF23 and revealed its relevant pathogenic role in various diseases. Most of these studies have been performed in adult individuals. However, the mineral metabolism of the child is, to a large extent, different from that of the adult because, in addition to bone remodeling, the child undergoes a specific process of endochondral ossification responsible for adequate mineralization of long bones’ metaphysis and growth in height. Vitamin D metabolism is known to be deeply involved in these processes. FGF23 might have an influence on bones’ growth as well as on the high and age-dependent serum phosphate concentrations found in infancy and childhood. However, the interaction between FGF23 and vitamin D in children is largely unknown. Thus, this review focuses on the following aspects of FGF23 metabolism in the pediatric age: circulating concentrations’ reference values, as well as those of other major variables involved in mineral homeostasis, and the relationship with vitamin D metabolism in the neonatal period, in vitamin D deficiency, in chronic kidney disease (CKD) and in hypophosphatemic disorders.

Establishment of Korean Pediatric Reference Intervals for Estradiol using Ultra-High-Performance Liquid Chromatography-Tandem Mass Spectrometry

BACKGROUND

Ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) is a reliable and accurate method for measuring steroid hormone levels. There is an increasing need for sensitive and precise methods to measure estradiol in pediatric patients. Here, we established reference intervals for estradiol in healthy children using a UHPLC-MS/MS-based method for the first time in South Korea.

METHODS

Serum estradiol was measured using a Sciex Triple Quad^TM 6500 + UHPLC-MS/MS (Sciex, Framingham, MA, USA). Reference intervals for estradiol were established according to the CLSI document EP28-A3c:2008. The reference intervals were validated using serum samples from 634 pediatric patients, including neonates, children, and adolescents. Among them, 389 specimens were used in analysis of the specimen acceptance time. Statistical analysis was performed using MedCalc (MedCalc, Ostend, Belgium) and Analyse-it (Analyse-it Software Ltd., Leeds, United Kingdom) software.

RESULTS

Reference intervals for boys (n = 297) were <16.6, <7.3, <19.0, <30.5, 7.6-96.5, and 10.6-134.4 pmol/L among those aged <1, 1-5, 6-9, 10-11, 12-14, and 15-17 years, respectively. Reference intervals for girls (n = 337) were <114.7, <24.2, <34.8, 8.0-177.0, 10.4-480.5, and 9.1-486.7 pmol/L among those aged <1, 1-5, 6-9, 10-11, 12-14, and 15-17 years, respectively. Overall, there was no effect of specimen acceptance time on estradiol measurements in boys or girls, except for that in the group aged 10-11 years.

CONCLUSIONS

The reference intervals for healthy children were validated using a UHPLC-MS/MS-based method. The highly analytical sensitive UHPLC-MS/MS method may be useful for estradiol determination in pediatric patients.

Free thyroxine measurement in clinical practice: how to optimize indications, analytical procedures, and interpretation criteria while waiting for global standardization

Thyroid dysfunctions are among the most common endocrine disorders and accurate biochemical testing is needed to confirm or rule out a diagnosis. Notably, true hyperthyroidism and hypothyroidism in the setting of a normal thyroid-stimulating hormone level are highly unlikely, making the assessment of free thyroxine (FT4) inappropriate in most new cases. However, FT4 measurement is integral in both the diagnosis and management of relevant central dysfunctions (central hypothyroidism and central hyperthyroidism) as well as for monitoring therapy in hyperthyroid patients treated with anti-thyroid drugs or radioiodine. In such settings, accurate FT4 quantification is required. Global standardization will improve the comparability of the results across laboratories and allow the development of common clinical decision limits in evidence-based guidelines. The International Federation of Clinical Chemistry and Laboratory Medicine Committee for Standardization of Thyroid Function Tests has undertaken FT4 immunoassay method comparison and recalibration studies and developed a reference measurement procedure that is currently being validated. However, technical and implementation challenges, including the establishment of different clinical decision limits for distinct patient groups, still remain. Accordingly, different assays and reference values cannot be interchanged. Two-way communication between the laboratory and clinical specialists is pivotal to properly select a reliable FT4 assay, establish reference intervals, investigate discordant results, and monitor the analytical and clinical performance of the method over time.

Pediatric reference interval verification for 17 specialized immunoassays and cancer markers on the Abbott Alinity i system in the CALIPER cohort of healthy children and adolescents

OBJECTIVES

Clinical laboratory investigation of autoimmune, metabolic, and oncologic disorders in children and adolescents relies on appropriateness of reference intervals (RIs). The Canadian Laboratory Initiative on Pediatric Reference Intervals (CALIPER) previously established comprehensive pediatric RIs for specialized immunoassays on the Abbott ARCHITECT system. Herein, we aim to verify performance on new Alinity i assays by evaluating sera collected from healthy children as per Clinical and Laboratory Standards Institute (CLSI) EP-28A3C guidelines.

METHODS

Precision, linearity, and method comparison experiments were completed for 17 specialized Alinity immunoassays, including cancer antigens, autoimmune peptides, and hormones. Sera collected from healthy children and adolescents (birth-18 years, n=100) were evaluated. CLSI-based verification was completed using previously established CALIPER RIs for ARCHITECT assays as the reference.

RESULTS

Of 17 specialized immunoassays assays, only anti-cyclic citrullinated peptides (anti-CCP) did not meet acceptable verification criterion (i.e., ≥90% of results within ARCHITECT reference CI). Anti-thyroglobulin, anti-thyroid peroxidase, and carcinoembryonic antigen did not require age-specific consideration beyond one year of age, with 63, 91, and 80% of samples equalling the limit of detection, respectively. Estimates were separated by sex for relevant assays (e.g., sex hormone binding globulin, total and free prostate specific antigen).

CONCLUSIONS

Findings support transferability of pediatric RIs on ARCHITECT system to the Alinity system for 16 specialized immunoassays in the CALIPER cohort and will be a useful resource for pediatric clinical laboratories using Alinity assays. Further work is needed to establish evidence-based interpretative recommendations for anti-CCP and continue to evaluate pediatric RI acceptability for newly available assay technologies.

Laboratory policies and practices for thyroid function tests in Croatia: survey on behalf of Working Group for Laboratory Endocrinology of the Croatian Society of Medical Biochemistry and Laboratory Medicine

Introduction

Laboratory plays important part in screening, diagnosis, and management of thyroid disorders. The aim of this study was to estimate current laboratory preanalytical, analytical and postanalytical practices and policies in Croatia.

Materials and methods

Working Group for Laboratory Endocrinology of the Croatian Society of Medical Biochemistry and Laboratory Medicine designed a questionnaire with 27 questions and statements regarding practices and protocols in measuring thyroid function tests. The survey was sent to 111 medical biochemistry laboratories participating in external quality assurance scheme for thyroid hormones organized by Croatian Centre for Quality Assessment in Laboratory Medicine. Data is presented as absolute numbers and proportions.

Results

Fifty-three participants returned the questionnaire. Response rate varied depending on question, yielding a total survey response rate of 46-48%. All respondents perform thyroid stimulating hormone (TSH). From all other thyroid tests, most performed is free thyroxine (37/53) and least TSH-stimulating immunoglobulin (1/53). Laboratories are using nine different immunoassay methods. One tenth of laboratories is verifying manufacturer’s declared limit of quantification for TSH and one third is verifying implemented reference intervals for all performed tests. Most of laboratories (91%) adopt the manufacturer’s reference interval for adult population. Reference intervals for TSH are reported with different percentiles (90, 95 or 99 percentiles).

Conclusion

This survey showed current practices and policies in Croatian laboratories regarding thyroid testing. The results identified some critical spots and will serve as a foundation in creating national guidelines in order to harmonize laboratory procedures in thyroid testing in Croatia.

Current State of Pediatric Reference Intervals and the Importance of Correctly Describing the Biochemistry of Child Development: A Review

Importance

Appropriately established pediatric reference intervals are critical to the clinical decision-making process and should reflect the physiologic changes that occur during healthy child development. Reference intervals used in pediatric care today remain highly inconsistent across a broad range of common clinical biomarkers.

Observations

This narrative review assesses biomarker-specific pediatric reference intervals and their clinical utility with respect to the underlying biological changes occurring during development. Pediatric reference intervals from PubMed-indexed articles published from January 2015 to April 2021, commercial laboratory websites, study cohorts, and pediatric reference interval books were all examined. Although large numbers of pediatric reference intervals are published for some biomarkers, very few are used by clinical and commercial laboratories. The patterns, extent, and timing of biomarker changes are highly variable, particularly during developmental stages with rapid physiologic changes. However, many pediatric reference intervals do not capture these changes and thus do not accurately reflect the underlying biochemistry of development, resulting in significant inconsistencies between reference intervals.

Conclusions and Relevance

There is a need to correctly describe the biochemistry of child development as well as to identify strategies to develop accurate and consistent pediatric reference intervals for improved pediatric care.

The Reference Intervals of Whole Blood Copper, Zinc, Calcium, Magnesium, and Iron in Infants Under 1 Year Old

Trace elements are essential nutrients for the optimal growth, development, and health of infants, and the reference intervals (RIs) from these trace elements in the blood are very important for an accurate assessment of the status of the elements. In this study, blood samples from a total of 13,446 infants (7206 boys and 6240 girls) were used, and the copper (Cu), zinc (Zn), calcium (Ca), magnesium (Mg), and iron (Fe) in their blood were determined using atomic absorption spectrometry. After clearing the data and removing any outliers, the gender- and age-specific RIs obtained from the Cu, Zn, Ca, Mg, and Fe in the infants' blood were established according to the principles of the Clinical and Laboratory Standards Institute (CLSI) C28-A3. In the multivariable analysis, after making the relevant adjustments for the confounding factors, the age of the infants showed a significant positive correlation with the concentrations of Zn, Ca, Mg, and Fe found in the blood (p<0.01). Furthermore, there were obvious differences in the Cu, Zn, and Ca levels in the blood according to the gender of the infants (p<0.01). As infants are in the critical period of their growth and development, the gender- and age-specific RIs may provide helpful guidance for the nutritional status of the Cu, Zn, Ca, Mg, and Fe elements in the infants' blood.

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.

Establishing reference intervals for islet autoantibodies in Han Chinese type 1 diabetes

Currently, islet autoantibodies (IAbs) constitute the most reliable marker for detecting the autoimmune process of type 1 diabetes (T1D). However, there are no appropriate reference intervals (RIs) to interpret the results of IAbs in China. In this study, we aimed to establish the RIs of four common IAbs based on the Han Chinese population and evaluate their clinical diagnostic values in patients with T1D. We collected 177 blood samples from healthy volunteers to detect the levels of IAbs directed against insulin (IAA), glutamic acid decarboxylase-65 (GADA), insulinoma antigen 2 (IA-2A), and zinc transporter-8 (ZnT8A) using a chemiluminescence immunoassay. RIs were calculated using nonparametric 95th percentile intervals in accordance with the Clinical and Laboratory Standards Institute guidelines, and their clinical diagnostic values were evaluated by detecting the levels of IAbs of 140 blood samples from patients with T1D in a clinical setting. We defined 138 individuals as the apparently healthy population from the 177 healthy volunteers based on the exclusion criteria. No association between the levels of the four IAbs and gender (p > .05) and age (p > .05) were found in the apparently healthy population. The combined RIs for GADA, IA-2A, ZnT8A, and IAA were 0-1.78 IU/mL, 0-3.91 IU/mL, 0-2.36 AU/mL, and 0-0.58 COI, respectively. Overall, the diagnostic efficiency for the four IAbs, especially for GADA and IAA, were improved by using the RIs established in this study. The RIs for IAbs established in this study will be a valuable tool for disease diagnosis and the therapeutic management of T1D in a clinical setting.

Pediatric Reference Intervals for Critical Point-of-Care Whole Blood Assays in the CALIPER Cohort of Healthy Children and Adolescents

OBJECTIVES

Point-of-care testing (POCT) is being increasingly adopted to support clinical care. Data for critical care parameters in healthy children on POCT instruments are lacking. We established comprehensive reference standards for several whole blood parameters on the Radiometer ABL90 FLEX PLUS blood gas analyzer in the Canadian Laboratory Initiative on Paediatric Reference Intervals (CALIPER) cohort.

METHODS

Approximately 300 healthy children and adolescents (age range, birth to <19 years; sex, boys and girls) were recruited with informed consent. Venous whole blood was collected (using heparinized syringes) and rapidly analyzed at the point of collection for pH, Pco2, Po2, carboxyhemoglobin, methemoglobin, lactate, and electrolytes on the ABL90 FLEX PLUS instrument. Reference intervals were established according to Clinical and Laboratory Standards Institute guidelines.

RESULTS

Of the parameters assessed, 6 required age partitioning; none required sex partitioning. Reference value distributions were consistent across the pediatric age range, demonstrating higher variation in the early neonatal period.

CONCLUSIONS

This study established reference standards for 10 critical care analytes in the CALIPER cohort for the first time. These data contribute to our understanding of normative pediatric values for venous electrolytes, metabolites, and blood gases on a modern POCT instrument, facilitating test interpretation in clinical settings that use these assays.

Age- and sex-specific reference intervals for thyroid hormones in a Chinese pediatrics: a prospective observational study of 1,279 healthy children

BACKGROUND

Thyroid hormones are essential for early neurocognitive development and growth and development in childhood and adolescence. However, the reference intervals (RIs) for thyroid hormones in Chinese pediatric individuals remain unclear. This study aimed to establish thyroid hormone RIs for a Chinese pediatric population according to appropriate age- and sex-specific partitioning.

METHODS

In this prospective observational study, a total of 1,279 healthy children (singletons, aged from 1 day to 12 years) were recruited, and serum samples were analyzed on a Mindray automated chemiluminescence immunoassay analyzer CL-6000i for thyroid hormone detection, including thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), free thyroxine (FT4), total triiodothyronine (T3), and total thyroxine (T4). Age and sex-specific RIs were established, and the corresponding 95% confidence intervals (CIs) were calculated in accordance with the Clinical Laboratory Standards Institute (CLSI) document C28-A3 guidelines.

RESULTS

Quantile testing revealed that the median (P50) and RIs [2.5^th percentile (P2.5)-97.5^th percentile (P97.5)] for TSH, FT3, T3, and T4 of males differed significantly from those of females (P<0.05), except for FT4 (P=0.483). For FT3 and T3, the RIs of males were higher than that of females, and the RI of T4 for males was narrower and higher than that of females [P2.5-P97.5: 72.33-171.60 vs. 72.31-176.27 nmol/L; P50: 116.75 vs. 113.47 nmol/L, P=0.011]. RIs for TSH, FT3, FT4, T3, and T4 showed sex- and age-specific properties and displayed a wide variation during the first month of life but gradually narrowed and concentrated with increasing age. In addition, RIs of TSH, FT3, FT4, and T3 in males differed significantly from females in the first month of life (TSH: 1.46-10.87 vs. 1.08-11.35 mIU/L; FT3: 2.96-7.08 vs. 2.35-7.27 pmol/L, FT4: 13.34-28.65 vs. 13.82-31.83 pmol/L; T3: 0.83-2.33 vs. 0.72-2.46 nmol/L). The RI of T4 also exhibited a difference between males and females in the 9- to 12-year age group (59.31-150.72 vs. 63.29-146.94 pmol/L for males and females, respectively).

CONCLUSIONS

Pediatric RIs of thyroid hormones display age- and sex-specific trends. The RIs established in this study will improve the accuracy of TSH assay result interpretations and clinical decision-making in clinical laboratories that utilize the Mindray analytical platform.

refineR: A Novel Algorithm for Reference Interval Estimation from Real-World Data

Reference intervals are essential for the interpretation of laboratory test results in medicine. We propose a novel indirect approach to estimate reference intervals from real-world data as an alternative to direct methods, which require samples from healthy individuals. The presented refineR algorithm separates the non-pathological distribution from the pathological distribution of observed test results using an inverse approach and identifies the model that best explains the non-pathological distribution. To evaluate its performance, we simulated test results from six common laboratory analytes with a varying location and fraction of pathological test results. Estimated reference intervals were compared to the ground truth, an alternative indirect method (kosmic), and the direct method (N = 120 and N = 400 samples). Overall, refineR achieved the lowest mean percentage error of all methods (2.77%). Analyzing the amount of reference intervals within ± 1 total error deviation from the ground truth, refineR (82.5%) was inferior to the direct method with N = 400 samples (90.1%), but outperformed kosmic (70.8%) and the direct method with N = 120 (67.4%). Additionally, reference intervals estimated from pediatric data were comparable to published direct method studies. In conclusion, the refineR algorithm enables precise estimation of reference intervals from real-world data and represents a viable complement to the direct method.

Establishing paediatric reference intervals for thyroid function tests in Croatian population on the Abbott Architect i2000

Introduction

Evaluation of thyroid function is often requested and therefore defining paediatric reference intervals (RIs) is of vital importance. Currently, there is a distinct lack of paediatric RIs for thyroid function tests in Croatia. Thus, we established RIs for thyroid stimulating hormone (TSH), total triiodothyronine (TT3), total thyroxine (TT4), free triiodothyronine (FT3) and free thyroxine (FT4) in the Croatian paediatric population.

Materials and methods

Reference intervals were calculated from 397 apparently healthy children, aged from 2 days to < 19 years. Serum samples were analysed for thyroid function tests on the Abbott Architect i2000. Age- and sex-specific 95% RIs with 90% confidence intervals were established according to Clinical and Laboratory Standards Institute guidelines. To express the magnitude of sex and age variation, standard deviation ratio (SDR) was calculated using two-level nested ANOVA. The criterion for considering partitioning reference values was set to SDR > 0.3.

Results

All thyroid function tests required age partitioning, confirmed by SDR above 0.3. There was no need for sex partitioning, confirmed by SDR below 0.3. Still, FT3 was partitioned due to visually noticeable sex related difference for the oldest group (12 years to < 19 years).

Conclusion

This is the first study to establish RIs for thyroid function tests in the Croatian paediatric population. We propose RIs for widely used Abbott platform, thus giving laboratories method- and population-specific paediatric RIs for thyroid function tests that should improve clinical test interpretation.

Pediatric reference interval verification for endocrine and fertility hormone assays on the Abbott Alinity system

OBJECTIVES

The Canadian Laboratory Initiative on Pediatric Reference Intervals (CALIPER) has developed an extensive database of reference intervals (RIs) for several biomarkers on various analytical systems. In this study, pediatric RIs were verified for key immunoassays on the Abbott Alinity system based on the analysis of healthy children samples and comparison to comprehensive RIs previously established for Abbott ARCHITECT assays.

METHODS

Analytical performance of Alinity immunoassays was first assessed. Subsequently, 100 serum samples from healthy children recruited with informed consent were analyzed for 16 Alinity immunoassays. The percentage of test results falling within published CALIPER ARCHITECT reference and confidence limits was determined. If ≥ 90% of test results fell within the confidence limits, they were considered verified based on CLSI guidelines. If <90% of test results fell within the confidence limits, additional samples were analyzed and new Alinity RIs were established.

RESULTS

Of the 16 immunoassays assessed, 13 met the criteria for verification with test results from ≥ 90% of healthy serum samples falling within the published ARCHITECT confidence limits. New CALIPER RIs were established for free thyroxine and prolactin on the Alinity system. Estradiol required special considerations in early life.

CONCLUSIONS

Our data demonstrate excellent concordance between ARCHITECT and Alinity immunoassays, as well as the robustness of previously established CALIPER RIs for most immunoassays, eliminating the need for de novo RI studies for most parameters. Availability of pediatric RIs for immunoassays on the Alinity system will assist clinical laboratories using this new platform and contribute to improved clinical decision-making.

Pediatric reference intervals for endocrine markers and fertility hormones in healthy children and adolescents on the Siemens Healthineers Atellica immunoassay system

OBJECTIVES

Rapid development in childhood and adolescence combined with lack of immunoassay standardization necessitates the establishment of age-, sex-, and assay-specific reference intervals for immunochemical markers. This study established reference intervals for 11 immunoassays on the new Siemens Healthineers Atellica® IM Analyzer in the healthy CALIPER cohort.

METHODS

A total of 600 healthy participants (birth to 18 years) were recruited from the community, and serum samples were collected with informed consent. After sample analysis, age- and sex-specific differences were assessed, and outliers were removed. Reference intervals were established using the robust method (40-<120 participants) or nonparametric method (≥120 participants).

RESULTS

Of the 11 immunoassays studied, nine required age partitioning (i.e., dehydroepiandrosterone-sulfate, estradiol, ferritin, folate, follicle-stimulating hormone, luteinizing hormone, progesterone, testosterone, vitamin B12), and seven required sex partitioning. Free thyroxine and thyroid-stimulating hormone demonstrated no significant age- and/or sex-specific differences.

CONCLUSIONS

Overall, the age- and sex-specific trends observed closely mirrored those previously reported by CALIPER on other platforms as well as other internationally recognized studies. However, established lower and upper limits demonstrated some discrepancies between published values from healthy cohorts on alternate analytical systems, highlighting differences between manufacturers and the need for platform-specific reference intervals for informed pediatric clinical decision-making.

Thyroid panel reference intervals in healthy children and adolescents: A Spanish cohort

OBJECTIVES

In children, thyroid hormones are essential for correct physical and neurological development. The recommended process for defining reference intervals (RIs) is the direct approach; however, indirect methods are an effective alternative. This study aimed to explore age- and sex-dependent relationships between serum concentrations of thyroid hormones in a large population-based cohort of healthy Spanish Caucasian children and calculate RIs.

MATERIAL AND METHODS

Results of serum thyroid-stimulating hormone (TSH) and free thyroxine (fT4) were collected from laboratory data of N (TSH = 23201; fT4 = 20728) patients aged 1 month - 15 years. These results were validated with a prospective study. Analyses of serum concentrations of TSH and fT4 were performed on ARCHITECT i2000 (Abbott Diagnostics, US). Percentiles (2.5th to 97.5th) were determined for each variable and taken as the RI.

RESULTS

No difference was found between serum TSH concentrations in male and female children of all age groups. A difference between serum fT4 concentrations in males and females and an age-dependent correlation for both sexes were found.

CONCLUSION

There is very little consensus on RIs in children. Our data confirm it is possible to use data mining techniques to calculate reliable and clinically useful RIs.

Updated ferritin reference intervals for the Roche Elecsys® immunoassay

Reference intervals (RI) for ferritin are the subject of some controversy, with indications that changes in lifestyle and demographics (e.g., obesity) have limited the validity of RIs established decades ago. Package insert RIs for the Roche Elecsys® immunoassay do not include expected values for pediatric (<17-20 years) or geriatric (>60 years) individuals; furthermore the female ranges were established in mostly premenopausal volunteers. To establish more robust RIs, we utilized 5 years of retrospective patient data from physician-ordered ferritin measurements and excluded results from patients with diagnoses known to affect ferritin concentrations. Ferritin results from 1438 unique patients aged 7 months to 91 years were included in the study. Continuous RIs were fitted for females (n = 951) and males (n = 487) as a function of age; these were then divided into clinically relevant sex-specific age breaks. RIs were established for pre-adolescent (<10 years), adolescent (10-17 years) and adult males, and for pediatric (<18 years), adult (18-50 years) and older (>50 years) females. Established RIs were verified using specimens obtained from healthy donors.

Diagnosis and management of iron deficiency in children with or without anemia: consensus recommendations of the SPOG Pediatric Hematology Working Group

Iron deficiency is the most prevalent nutritional deficiency affecting children and adolescents worldwide. A consistent body of epidemiological data demonstrates an increased incidence of iron deficiency at three timepoints: in the neonatal period, in preschool children, and in adolescents, where it particularly affects females.Conclusion: This narrative review focuses on the most suggestive symptoms of iron deficiency in childhood, describes the diagnostic procedures in situations with or without anemia, and provides Swiss expert-based management recommendations for the pediatric context.What is Known:• Iron deficiency (ID) is one of the most common challenges faced by pediatricians.• Significant progress in the diagnosis and therapy of ID has been made over the last decade.What is New:• Our expert panel provides ID management recommendations based on the best available evidence.• They include strategies for ID diagnosis and therapy, both oral and intravenous.