Estimating reference intervals

Atrial dimension reference values in healthy participants using the biplane/monoplane method for clinical and research use

AIM

To provide reference values of the dimensions of the left and right atrium (RA) obtained using the biplane and monoplane methods, respectively, on two- and four-chamber views, which represent the standard projections acquired in clinical practice, and correlation with body surface area (BSA), age, and gender.

MATERIALS AND METHODS

Healthy volunteers, M:F = 1:1, including five participants per gender and age decile from 20 to 70 years, who underwent cardiovascular magnetic resonance imaging (CMR) were enrolled prospectively. Normal atrial reference values were calculated for male and female subpopulations and stratified by age. Atrial areas and volumes were assessed both as absolute values and indexed to BSA. Differences among genders and correlation with age were assessed. Intra- and interobserver reproducibility were assessed in a subpopulation.

RESULTS

Fifty participants (mean age 43.3 ± 14 years, 25 men) were evaluated. Image analysis took <1 minute for each subject (mean time 30 ± 5 seconds). Intra- and interobserver reproducibility were excellent (ICC >0.85 for all datasets). RA areas were significantly higher in males (p=0.0001). The left atrial (LA) surface did not show significant differences among genders. Atrial areas normalised to BSA did not show significant gender differences. Both right and left absolute atrial volumes turned out to be significantly higher in males (p=0.0001 and p=0.0047, respectively), and normalised to BSA remained significantly different only for the RA (p=0.0006). Neither atrial volume nor areas showed significant correlation with age.

CONCLUSIONS

The monoplane method is a fast and reproducible technique to assess atrial dimensions. Absolute atrial dimensions show significant variations among genders. Gender-specific reference ranges for atrial dimensions are recommended.

Feasibility of using real-world free thyroxine data from the US and Europe to enable fast and efficient transfer of reference intervals from one population to another

Objectives

The direct approach for determining reference intervals (RIs) is not always practical. This study aimed to generate evidence that a real-world data (RWD) approach could be applied to transfer free thyroxine RIs determined in one population to a second population, presenting an alternative to performing multiple RI determinations.

Design and methods

Two datasets (US, n = 10,000; Europe, n = 10,000) were created from existing RWD. Descriptive statistics, density plots and cumulative distributions were produced for each data set and comparisons made. Cumulative probabilities at the lower and upper limits of the RIs were identified using an empirical cumulative distribution function. According to these probabilities, estimated percentiles for each dataset and estimated differences between the two sets of percentiles were obtained by case resampling bootstrapping. The estimated differences were then evaluated against a pre-determined acceptance criterion of ≤7.8% (inter-individual biological variability). The direct approach was used to validate the RWD approach.

Results

The RWD approach provided similar descriptive statistics for both populations (mean: US = 16.1 pmol/L, Europe = 16.4 pmol/L; median: US = 15.4 pmol/L, Europe = 15.8 pmol/L). Differences between the estimated percentiles at the upper and lower limits of the RIs fulfilled the pre-determined acceptance criterion and the density plots and cumulative distributions demonstrated population homogeneity. Similar RI distributions were observed using the direct approach.

Conclusions

This study provides evidence that a RWD approach can be used to transfer RIs determined in one population to another.

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.

Baseline rotational thromboelastometry (ROTEM) values in a healthy, diverse obstetric population and parameter changes by pregnancy-induced comorbidities

Background

Point-of-care testing provides a representation of the patient's coagulability status during effective postpartum hemorrhage management. Baseline values of rotational thromboelastometry (ROTEM) have not yet been reported in a heterogeneous obstetric population. This study aimed to establish a baseline for a diverse population representative of the United States. The secondary aim was to evaluate the association of these hematologic parameters with comorbidities, race, and socioeconomic factors.

Methods

The study was a retrospective review of collected ROTEM values of women undergoing vaginal or cesarean delivery with a history of or at risk for postpartum hemorrhage. Patients were divided into healthy and comorbid groups. Exclusion criteria for both groups included active or recent bleeding, receipt of blood products or clot-enhancing factors, and liver disease. Mean values of ROTEM by race and comorbidities were included. Median values were reported for intrinsic pathway thromboelastometry (INTEM), extrinsic pathway thromboelastometry (EXTEM), and fibrin polymerization thromboelastometry (FIBTEM) amplitude at 10 minutes (A10) and 20 minutes (A20), coagulation time, clot formation time, and maximum clot firmness.

Results

A total of 681 records were reviewed; 485 met inclusion criteria, and 267 met healthy criteria. The mean (standard deviation) demographics for maternal age (years), body mass index (kg/m2), and gestational age (weeks) were 32.2 (5.7), 34 (7.3), and 35.4 (5), respectively. The median INTEM, EXTEM, and FIBTEM A10 were 63, 65, and 23 mm. The mean for INTEM, EXTEM, and FIBTEM A10 was increased for those who were Black or obese, whereas a decreased FIBTEM and EXTEM A10 was noted in those who were Asian or those who had the hemolysis, elevated liver enzymes, low platelet syndrome.

Conclusions

Our heterogeneous population presents ROTEM values within the interquartile range of those previously reported in European studies. Black race, obesity, and preeclampsia were associated with hypercoagulable profiles.

Concentrations of endogenous sex steroid hormones and SHBG in healthy postmenopausal women

Studies reporting age-specific reference ranges of endogenous sex steroid hormones in postmenopausal women are relatively scarce. If levels differ by age, dosing and treatment regimens should vary among postmenopausal women accordingly. Our objective was to establish reference ranges for sex steroid hormones and sex hormone binding globulin (SHBG) by age group and overall, and to investigate their association with demographic characteristics. Serum samples were obtained from 1207 healthy postmenopausal women aged 41-92, not using hormone therapy, at the baseline visit of 3 clinical trials. Estrone (E1), estradiol (E2), and total testosterone (T) were measured by radioimmunoassay with preceding purification steps; SHBG was measured by direct chemiluminescent immunoassay. Free T (FT) was calculated. Women were categorized by 5-year age groups. There was little change in the mean estrogen levels among the different age groups (E2: 9-12 pg/mL; E1: 33-35 pg/mL). Mean total T levels increased gradually with age from 19.9-26.2 ng/dL, but FT mean levels were relatively constant (3.7-4.6 pg/mL). Mean SHBG levels increased with age from 43-68 nmol/L. A generalized linear model tested the association of each demographic characteristic with the hormones and SHBG. A significant association was derived. Our study provides valuable insight into the profiles of serum sex steroid hormones and SHBG in different healthy postmenopausal women aged 41-92 years.

An International Survey of Glucose-6-Phosphate Dehydrogenase Laboratory Reporting Practices

CONTEXT.—

Glucose-6-phosphate dehydrogenase (G6PD) activity is used in the evaluation of hemolysis risk in patients being assessed for G6PD deficiency. A long-acting 8-aminoquinoline drug (tafenoquine) used in malaria treatment is contraindicated in patients with G6PD deficiency (<70% normal G6PD activity). The current state of G6PD reporting practices to support clinical eligibility assessment is poorly understood.

OBJECTIVE.—

To assess clinical laboratory reporting practices for G6PD testing.

DESIGN.—

In October 2019 and October 2020, voluntary questionnaires were distributed to 327 and 324 laboratories participating in the College of American Pathologists G6PD proficiency testing (PT).

RESULTS.—

Two hundred fifty-seven and 119 laboratories responded to the 2019 and 2020 questionnaires, respectively. Few laboratories have received clinical questions about average normal G6PD activity (US/Canada, 2.0% [3 of 149]; international, 8.4% [9 of 107]), whereas slightly more have determined the average normal G6PD activity for their own assay and patient populations (US/Canada, 6.7% [10 of 149]; international, 19.4% [21 of 108]). Few laboratories report G6PD activity in percent of normal format (US/Canada, 2.7% [4 of 149]; international, 8.3% [9 of 108]). The most common unit of measurement in use for quantitative G6PD reporting is unit per gram of hemoglobin. Reference intervals vary based on assay, reaction temperature, and participant laboratory and demonstrate moderate correlation (r = .46-.51) to G6PD activity measured from a "normal" PT challenge specimen. Nearly half of participants (47.8% [85 of 178]) categorized a quantitatively "intermediate" G6PD PT challenge as "normal" when using qualitative assays.

CONCLUSIONS.—

Percent of normal G6PD activity reporting would facilitate patient eligibility assessment for drugs, such as tafenoquine. Quantitative assays are better able to differentiate "intermediate" specimens than qualitative assays.

Baseline parameters for non-activated rotational thromboelastometry tests with and without heparinase in healthy pregnant women at term gestation

OBJECTIVE

To determine the normal values for non-activated thromboelastometry parameters among pregnant women.

DESIGN

Prospective, observational study.

SETTING

Tertiary care hospital.

PATIENTS

Non-laboring women at term gestation without history of bleeding or clotting disorder or anticoagulation use.

INTERVENTIONS

Venous blood samples were collected and ROTEM® was performed using NATEM and NaHEPTEM assays.

MEASUREMENTS

Reference ranges were derived by calculating 2.5 and 97.5 percentiles for the following parameters: clotting time (CT), clot formation time (CFT), amplitude at 10 (A10) and 20 min (A20), alpha angle, maximum clot firmness (MCF), and lysis index at 30 (LI30) and 60 min (LI60). The NATEM/NaHEPTEM CT ratio was calculated to determine the baseline ratio in term pregnant women.

MAIN RESULTS

146 women were screened and 120 were enrolled. The median age was 34 years [31-36], median gestational age was 39.1 weeks [38.3-39.3], and median parity was 1 [0-2]. Median pre-delivery platelet and hematocrit levels were within the normal ranges. The reference ranges for NATEM parameters were: CT (232-759 (s)), CFT (69-243 (s)), alpha angle (50-77 (°)), A10 (44-69 (mm)), A20 (54-75 (mm)), MCF (57-77 (mm)), LI30 (100-100 (%)), LI60 (90-100 (%)). The reference ranges for NaHEPTEM parameters were: CT (224-717 (s)), CFT (66-210 (s)), alpha angle (53-77 (°)), A10 (44-67 (mm)), A20 (55-73 (mm)), MCF (58-74 (mm)), LI30 (99-100 (%)), LI60 (90-100 (%)). The NATEM to NaHEPTEM CT ratio reference range was 0.73-1.3.

CONCLUSIONS

This study is the first to our knowledge to report reference ranges for non-activated ROTEM® tests with and without heparinase in non-laboring term pregnant women. These reference ranges may serve as a baseline comparison and may be useful for future research on anticoagulation management in pregnancy.

Establishing reference interval for thyroid-stimulating hormone in children below two-year ages in Pakistani population

Introduction

Reference intervals (RIs) of thyroid-stimulating hormone (TSH) and free thyroxine (FT4) are age, assay and population specific. Currently, the age and assay-specific RIs for TSH are not available for children under two years of age. This study aimed to establish reference intervals for serum concentrations of TSH and FT4 in healthy children aged 1–24 months as per CLSI C28-A3 guidelines.

Methods

This prospective cross-sectional study was conducted in children from 1 to 24 months visiting the clinical laboratory for serum vitamin D testing but without any recent illness, hospitalization, medication and history of maternal thyroid diseases from August 2018 to March 2019 were invited to participate in the study.

Serum TSH and FT4 were measured on ADVIA Centaur (Siemens Diagnostics, US), using chemiluminescence immunoassay. Kolmogorov–Smirnov test assessed normality of the data and RIs based on central 95% of the population were established using the non-parametric approach.

Results

After excluding one subject with confirmed congenital hypothyroidism, a total of 131 children were included in the study. The median (IQR) age of the study subjects was 12 months (11), and majority 78 (59.5%) were boys. The RIs were established using non-parametric approach as the data was not normally distributed. Reference interval for TSH was 0.73–4.94 μIU/mL and for FT4 was 0.81–1.51 ng/dl.

Conclusion

We established assay-specific RIs for serum TSH and FT4 in children aged 1–24 months in our population. The RIs were slightly lower from RIs developed on other platforms in different population.

•

Reference intervals (RIs) of TSH and FT4 are age, assay and population specific.

•

RIs of TSH & FT4 for <2 yrs Pakistani children on Advia Centaur analyzer not available.

•

The RIs for TSH (0.73–4.94μIU/mL) and FT4 (0.81–1.51 ng/dl) for < 2 yrs old children.

Reference intervals in Danish children and adolescents for bone turnover markers carboxy-terminal cross-linked telopeptide of type I collagen (β-CTX), pro-collagen type I N-terminal propeptide (PINP), osteocalcin (OC) and bone-specific alkaline phosphatase (bone ALP)

PURPOSE

Bone turnover markers (BTM) are gaining ground in clinical practice but to fully use their potential there is a need for establishing valid reference intervals (RI). Consequently, the purpose of the study was to establish general RI as well as suggested clinical RI for carboxy-terminal cross-linked telopeptide of type I collagen (β-CTX), pro-collagen type I N-terminal propeptide (PINP), osteocalcin (OC) and bone-specific alkaline phosphatase (bone ALP) in children and adolescents.

METHOD

BTM were measured on Danish children and adolescents participating in the CHAMPS-study DK. A total of 762 participants were included (8-18 years, 50.4% girls) contributing a total of 1410 study visits. The RI was calculated based on 2-years age spans. Participants with biochemical signs of metabolic bone disease were excluded.

RESULTS

The differences in RI between age groups clearly reflect changes in growth with an initial increase in BTM, greatest in boys, and a subsequent decrease most pronounced in girls. β-CTX and PINP are markers most affected by these changes, compared to OC and bone ALP. The suggested clinical 95% RI included participants with vitamin D insufficiency but no biochemical signs of metabolic bone disease which did not markedly alter the RI.

CONCLUSION

RI for β-CTX, PINP, OC and bone ALP varies with age and sex. β-CTX and PINP which reflect bone resorption and formation processes are mostly affected by these changes. We suggest a set of clinically applicable 95% RI for the four BTM to heighten the usefulness and generalizability of the RI.

Reference ranges for clinical electrophysiology of vision

Introduction

Establishing robust reference intervals for clinical procedures has received much attention from international clinical laboratories, with approved guidelines. Physiological measurement laboratories have given this topic less attention; however, most of the principles are transferable.

Methods

Herein, we summarise those principles and expand them to cover bilateral measurements and one-tailed reference intervals, which are common issues for those interpreting clinical visual electrophysiology tests such as electroretinograms (ERGs), visual evoked potentials (VEPs) and electrooculograms (EOGs).

Results

The gold standard process of establishing and defining reference intervals, which are adequately reliable, entails collecting data from a minimum of 120 suitable reference individuals for each partition (e.g. sex, age) and defining limits with nonparametric methods. Parametric techniques may be used under some conditions. A brief outline of methods for defining reference limits from patient data (indirect sampling) is given. Reference intervals established elsewhere, or with older protocols, can be transferred or verified with as few as 40 and 20 suitable reference individuals, respectively. Consideration is given to small numbers of reference subjects, interpretation of serial measurements using subject-based reference values, multidimensional reference regions and age-dependent reference values. Bilateral measurements, despite their correlation, can be used to improve reference intervals although additional care is required in computing the confidence in the reference interval or the reference interval itself when bilateral measurements are only available from some of subjects.

Discussion

Good quality reference limits minimise false-positive and false-negative results, thereby maximising the clinical utility and patient benefit. Quality indicators include using appropriately sized reference datasets with appropriate numerical handling for reporting; using subject-based reference limits where appropriate; and limiting tests for each patient to only those which are clinically indicated, independent and highly discriminating.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10633-021-09831-1.

Reference ranges ("normal values") for cardiovascular magnetic resonance (CMR) in adults and children: 2020 update

Cardiovascular magnetic resonance (CMR) enables assessment and quantification of morphological and functional parameters of the heart, including chamber size and function, diameters of the aorta and pulmonary arteries, flow and myocardial relaxation times. Knowledge of reference ranges ("normal values") for quantitative CMR is crucial to interpretation of results and to distinguish normal from disease. Compared to the previous version of this review published in 2015, we present updated and expanded reference values for morphological and functional CMR parameters of the cardiovascular system based on the peer-reviewed literature and current CMR techniques. Further, databases and references for deep learning methods are included.

Establishing the lower limits of total serum testosterone among Chinese proven fertile men who received treatment of assisted reproductive technology

Testosterone (T) plays a crucial role in spermatogenesis because extremely low levels of intratesticular T lead to correspondingly low serum levels of total T (tT), severe disorders of spermatogenesis, and male sterility. However, there is little consensus on the lower limits of serum tT in proven fertile men undergoing assisted reproductive technology treatments in Chinese or other Asian populations. We aimed to establish the reference range of serum tT based on a population of 868 fertile Chinese men undergoing in vitro fertilization or intracytoplasmic sperm injection and embryo transfer (IVF/ICSI-ET) treatments. We defined a fertile man as having had a live baby with his partner as recorded in our IVF registration system. The lower limits of serum tT were established using a Siemens IMMULITE 2000 chemiluminescent system. The 1st, 2.5th, and 5th percentiles and their 95% confidence intervals (CIs) were 3.6 (95% CI: 2.7-4.1) nmol l-1, 4.3 (95% CI: 4.1-5.0) nmol l-1, and 5.6 (95% CI: 4.8-5.8) nmol l-1, respectively. Using the linear correlation of serum tT between the Siemens platform and a liquid chromatography-tandem mass spectrometry platform, the calculated lower limits of serum tT were also established for fertile Chinese men undergoing IVF/ICSI-ET treatments, which will benefit the clinical diagnosis and treatment of male infertility during such procedures.

Effects of age and sex on osteocalcin and bone-specific alkaline phosphatase-reference intervals and confounders for two bone formation markers

Bone formation markers bone-specific alkaline phosphatase and osteocalcin are used in many clinical situations. Therefore, we calculated reference intervals for the two markers and investigated how they are influenced by several factors including sex and age. Furthermore, we established clinically relevant reference intervals for the two markers.

OBJECTIVE

The bone turnover markers (BTMs), bone-specific alkaline phosphatase (bone ALP), and osteocalcin (OC), are frequently measured formation markers. The purpose of this study was to establish reference intervals (RIs) for the two BTMs in a general adult Danish population.

METHODS

Bone ALP and OC were measured on the iSYS (IDS Plc) automatic analyzer in samples from the Danish Health2006 5-year follow-up study on serum from 2308 participants (54% women, age range 24-76). Participants with self-reported diagnosis of osteoporosis or receiving hormonal replacement were excluded from analyses while participants on hormonal contraceptives were included.

RESULTS

The geometric mean and 95%RI for bone ALP were 13.9 μg/L (7.6-25.6) for men and 13.8 μg/L (7.0-27.4) for women, while for OC 16.0 μg/L (7.5-34.4) for men and 18.6 μg/L (8.1-42.9) for women. Levels of bone ALP increased with increasing age (β 1.004, p < 0.001), while female sex had no effect. OC levels decreased with increasing age (β 0.998, p = 0.009) and increased with female sex (β 1.104, p < 0.001). Based on our findings, we propose for bone ALP and OC three clinical RIs for men based on age and three clinical RI for women based on age and menopausal status.

CONCLUSION

The RI for bone ALP and OC varies with age and sex and the BTMs are influenced differently by the two factors. Consequently, the need for establishing valid RIs is of great importance before the full potential of BTM can be used in clinical practice.

Widespread Incorrect Implementation of the Hoffmann Method, the Correct Approach, and Modern Alternatives

Objectives

The Hoffmann method is a procedure for reference interval estimation using routine clinical results. Many authors incorrectly prepare Hoffmann plots on a linear rather than normal probability scale. We explore the consequences.

Methods

This was investigated algebraically, by random number simulations (45 simulations, n = 100,000 each) and using clinical data sets. Strategies compared were: Hoffmann's method as originally and incorrectly implemented, Bhattacharya's method, and maximum likelihood (ML). All R source code and data sets are provided.

Results

As the proportion of healthy individuals approaches 1, the incorrect approach generates reference interval estimates of approximately μH ± 1.19 σH delineating the central 77% of the healthy subpopulation, not the central 95%. Inappropriately narrow reference interval estimates were seen on random simulations and clinical data sets. ML methods performed best.

Conclusions

The erroneous variant Hoffmann method should not be used. ML methods outperform others and are not restricted by Gaussian assumptions.

Reference intervals of trimester-specific thyroid stimulating hormone and free thyroxine in Chinese women established by experimental and statistical methods

BACKGROUND

As a result of physiological and metabolic changes during pregnancy, thyroid hormones can be affected significantly throughout entire three trimesters. According to the guidelines published by American Thyroid Association in 2017, it is strongly recommended to establish population-based trimester-specific and assay method-specific reference intervals (RIs) using local population.

METHODS

A total of 1209 pregnant women without personal or family history of thyroid disease were recruited from July 2015 to April 2017 at Beijing Obstetrics and Gynecology Hospital. Those initially selected patients were further tested for TSH, FT4 and thyroid peroxidase antibody (aTPO), performed on the chemiluminescent platform Siemens ADVIA Centaur^® XP. Only patients tested negative for aTPO were included in reference interval establishment. RIs for both TSH and FT4 were determined as 2.5th percentile to 97.5th percentile on the data distribution.

RESULTS

The TSH and FT4 trimester-specific RIs were as follows: 0.59-3.54 mIU/L, 11.8-18.4 pmol/L (n = 188, 1st trimester); 0.80-4.46 mIU/L, 11.6-17.4 pmol/L (n = 133, 2nd trimester); 0.72-4.19 mIU/L, 9.7-15.1 pmol/L (n = 157, 3rd trimester). The RIs of TSH and FT4 determined by Hoffmann method for first trimester outpatient pregnant women were 0.33-3.96 mIU/L (n = 9924) and 11.7-17.5 pmol/L (n = 10039), respectively.

CONCLUSION

Trimester-specific thyroid function tests RIs are distinct from those provided by assay manufacturers. The RIs determined by direct sampling and Hoffmann indirect calculation showed no statistical difference.

Comparison of two automated assays of BTM (CTX and P1NP) and reference intervals in a Danish population

Bone turnover markers are used for monitoring osteoporosis treatment. Therefore, we evaluated the agreement between different assays for CTX and PINP and established reference intervals in a cohort of 2300 individuals. We found poor agreement between assays and different reference intervals. This highlights the importance of harmonization of the assays.

INTRODUCTION

Two reference markers for bone turnover have been proposed: CTX bone resorption and P1NP for bone formation. The purpose of the current study was to establish reference intervals for the two markers in a Danish cohort and to determine the agreement on the two platforms.

METHODS

Fasting sera from 2308 individuals (1250 males and 1058 females, age range 24-76 years) participating in the Health2006 study were analyzed for CTX and P1NP using the automated IDS-iSYS analyzer and the automated Cobas e411 analyzer. Participants in anti-osteoporotic treatment were excluded, while subjects on hormonal contraceptives were included.

RESULTS

There was significant disagreement between both the two P1NP assays with a mean difference of -3 μg/L (LoA -19 to 14) (p < 0.001) and the two CTX assays with a mean difference of 13 ng/L (LoA-187 to 214) (p < 0.001). For CTX, there was a systematic bias: at low values, Cobas measured a higher value than iSYS and at higher concentrations, iSYS measured increasingly higher values than Cobas. Based on the results, we propose three reference intervals for each sex: 25-29, 30-39, and 40-80 years for men, and 25-29, >30 (pre-menopausal), and >30 years (post-menopausal) for women.

CONCLUSIONS

There is significant disagreement between the IDS-iSYS and Roche Cobas assays for both reference markers. Consequently, the reference intervals for an adult, healthy population are different depending on the analysis method used. Therefore, repeated measurements of patient samples used for monitoring of treatment should be done on the same assay. Moreover, assay-specific reference intervals should be used. Harmonization of assays for BTM is highly warranted.

Pediatric-specific reference intervals in a nationally representative sample of Iranian children and adolescents: the CASPIAN-III study

BACKGROUND

This study aimed to determine for the first time the age- and gender-specific reference intervals for biomarkers of bone, metabolism, nutrition, and obesity in a nationally representative sample of the Iranian children and adolescents.

METHODS

We assessed the data of blood samples obtained from healthy Iranian children and adolescents, aged 7 to 19 years. The reference intervals of glucose, lipid profile, liver enzymes, zinc, copper, chromium, magnesium, and 25-hydroxy vitamin D [25(OH)D] were determined according to the Clinical & Laboratory Standards Institute C28-A3 guidelines. The reference intervals were partitioned using the Harris-Boyd method according to age and gender.

RESULTS

The study population consisted of 4800 school students (50% boys, mean age of 13.8 years). Twelve chemistry analyses were partitioned by age and gender, displaying the range of results between the 2.5th to 97.5th percentiles. Significant differences existed only between boys and girls at 18 to 19 years of age for low density lipoprotein-cholesterol. 25(OH)D had the only reference interval that was similar to all age groups and both sexes.

CONCLUSIONS

This study presented the first national database of reference intervals for a number of biochemical markers in Iranian children and adolescents. It is the first report of its kind from the Middle East and North Africa. The findings underscore the importance of providing reference intervals in different ethnicities and in various regions.

Reference range for thyrotropin. Post hoc assessment

Setting the reference range for thyrotropin (TSH) remains a matter of ongoing controversy.

PATIENTS, METHODS

We used an indirect method to determine the TSH reference range post hoc in a large sample. A total of 399 well characterised subjects showing no evidence of thyroid dysfunction were selected for definition of the TSH reference limits according to the method of Katayev et al.. To this end, the cumulative frequency was plotted against the individual logarithmic TSH values. Reference limits were calculated by extrapolating the middle linear part of the regression line to obtain the cut-offs for the 95% confidence interval. We also examined biological variation in a sample of 65 subjects with repeat measurements to establish reference change values (RCVs).

RESULTS

Based on these, the reference interval obtained by the novel technique was in close agreement with the conventionally established limits, but differed significantly from earlier recommendations.

DISCUSSION

Following unverified recommendations could result in a portion of patients with subclinical thyroid dysfunctions being missed, an important consideration in a setting with a high prevalence of thyroid autonomy.

CONCLUSION

Indirect post hoc verification of reference intervals from a large retrospective sample is a modern approach that gives plausible results. The method seems particularly useful to assess the adequacy and performance of reference limits reported or established by others in a particular setting. The present data should encourage re-evaluation of reference systems on a broader scale.

Establish and verify TSH reference intervals using optimized statistical method by analyzing laboratory-stored data

OBJECTIVE

To establish reference intervals using an optimized statistical method by collecting available laboratory data of thyroid stimulating hormone (TSH), and then to verify with the laboratory-present reference intervals.

METHODS

TSH RIs of the total population and different races, genders, age, source of sample are established through improved Hoffmann and Katayev's method with TSH test results data from Jan 2010 to April 2012 were collected, and finally conduct comparative verification with the laboratory present RIs.

RESULTS

According to the improved method, we get various RIs of different sample populations. On comparing with the laboratory current RI (0.270-4.200 mIU/L) most reference change values (RCV) were within acceptable limits. Only lower limit of Han male, Uygur male and out-patient male populations outwith acceptable limits. On excluding the different values, finally, the new RI by the optimized statistical method is 0.233-4.979 mIU/L. Because the new RI expanded the current RI and was not different from the current RI, it was indicated that new RI could be used to verify the laboratory current RIs and seen as the current RI's confidence interval (CI).

INFERENCE

TSH RIs established by optimized Hoffmann's and Katayev's methods is viable and can be used to verify RIs provided by manufacturers or other laboratories.

Reference intervals of bone turnover markers determined by using their curve-fitting valley for adult females in China

SUMMARY

The reference values for bone turnover markers (BTMs) have a significant role in the diagnosis, monitoring, and treatment of metabolic bone disease. This study proposes that the peak value of bone mineral density and the trough value for the BTM curve can be used to determine the reference range of BTM.

INTRODUCTION

The aim of this study is to determine the reference intervals of BTMs for adult females in China with an attempt to reference the peak bone mineral density (BMD) with the corresponding BTM valley.

METHODS

This study included 546 premenopausal and 394 postmenopausal women. The levels of several BTMs were determined, and the BMD was measured using a dual-energy X-ray absorptiometry.

RESULTS

The BTMs of postmenopausal women were 17-96 % higher than premenopausal women. The change of BTM with age presented an optimal goodness-of-fit according to the cubic regression model (R (2) = 0.074-0.346, all P = 0.000). All kinds of BTM levels were positively correlated with age in premenopausal women aged 27-56 years old (r = 0.167-0.502, P = 0.023-0.000). Except for uCTX, the BTM reference value determined using a curve-fitting valley was significantly lower than the reference values for premenopausal women. The BTM reference values determined in this study were also significantly different from the reference values given by the manufacturers of the reagents used.

CONCLUSIONS

This study found that the changes of level with age of BTMs in Chinese women present an optimal goodness-of-fit according to the cubic regression model. The fitting valley corresponds to the BMD fitting peak and may possibly be an effective means of determining the BTM reference intervals.

Lower reference limits of quantitative cord glucose-6-phosphate dehydrogenase estimated from healthy term neonates according to the Clinical and Laboratory Standards Institute guidelines: a cross sectional retrospective study

BACKGROUND

Previous studies have reported the lower reference limit (LRL) of quantitative cord glucose-6-phosphate dehydrogenase (G6PD), but they have not used approved international statistical methodology. Using common standards is expecting to yield more true findings. Therefore, we aimed to estimate LRL of quantitative G6PD detection in healthy term neonates by using statistical analyses endorsed by the International Federation of Clinical Chemistry (IFCC) and the Clinical and Laboratory Standards Institute (CLSI) for reference interval estimation.

METHODS

This cross sectional retrospective study was performed at King Abdulaziz Hospital, Saudi Arabia, between March 2010 and June 2012. The study monitored consecutive neonates born to mothers from one Arab Muslim tribe that was assumed to have a low prevalence of G6PD-deficiency. Neonates that satisfied the following criteria were included: full-term birth (37 weeks); no admission to the special care nursery; no phototherapy treatment; negative direct antiglobulin test; and fathers of female neonates were from the same mothers' tribe. The G6PD activity (Units/gram Hemoglobin) was measured spectrophotometrically by an automated kit. This study used statistical analyses endorsed by IFCC and CLSI for reference interval estimation. The 2.5th percentiles and the corresponding 95% confidence intervals (CI) were estimated as LRLs, both in presence and absence of outliers.

RESULTS

207 males and 188 females term neonates who had cord blood quantitative G6PD testing met the inclusion criteria. Method of Horn detected 20 G6PD values as outliers (8 males and 12 females). Distributions of quantitative cord G6PD values exhibited a normal distribution in absence of the outliers only. The Harris-Boyd method and proportion criteria revealed that combined gender LRLs were reliable. The combined bootstrap LRL in presence of the outliers was 10.0 (95% CI: 7.5-10.7) and the combined parametric LRL in absence of the outliers was 11.0 (95% CI: 10.5-11.3).

CONCLUSION

These results contribute to the LRL of quantitative cord G6PD detection in full-term neonates. They are transferable to another laboratory when pre-analytical factors and testing methods are comparable and the IFCC-CLSI requirements of transference are satisfied. We are suggesting using estimated LRL in absence of the outliers as mislabeling G6PD-deficient neonates as normal is intolerable whereas mislabeling G6PD-normal neonates as deficient is tolerable.

Bone turnover markers: use in osteoporosis

Biochemical markers of bone turnover (bone turnover markers, BTMs) can be used to study changes in bone remodelling in osteoporosis. Investigators and clinicians should be aware of the appropriate sample collection and storage conditions for optimum measurements of these markers. Improvements in the variability of BTM measurements have resulted from the development of assays for automated analysers, and from international consensus regarding their use. Appropriate reference intervals should be used for the optimum interpretation of results. BTMs can provide information that is useful for the management of patients with osteoporosis, for both the initial clinical assessment and for guiding and monitoring of treatment. BTMs are clinically useful to determine possible causes of secondary osteoporosis by identifying patients with high bone turnover and rapid bone loss. In the follow-up of treatment response, BTM levels respond rapidly to both anabolic and antiresorptive treatments. BTM changes can also be used for understanding the mechanism of action of drugs in development and identifying the correct dose; they are also potentially useful as surrogate biomarkers for fracture.

Automated cerebrospinal fluid cell counts using the Sysmex XE-5000: is it time for new reference ranges?

The main objectives of the study were to compare manual and automated WBC counts on clear cerebrospinal fluid (CSF) samples. Clear CSF samples from 200 adults and children were studied. Cell counts were performed manually using a hemocytometer and then analyzed on the Sysmex XE-5000. Descriptive statistics and Spearman correlation for nonparametric data were used for method comparison. Manual WBC counts ranged from 0 to 702 cells/μL, and Sysmex counts ranged from 0 to 629 cells/μL. The Spearman rank correlation coefficient for the entire range of data was 0.77 (P < .001); however, the correlation was weaker at the low end of the data spectrum. For manual WBC ranges of 0 to 5 cells/μL and 0 to 10 cells/μL, the corresponding Sysmex 0 to 95th percentile ranges were 0 to 23 cells/μL and 0 to 27 cells/μL, respectively. The results suggest that larger studies are necessary to determine new reference ranges for automated CSF WBC counts.