The Nordic Reference Interval Project 2000: recommended reference intervals for 25 common biochemical properties

Sharing reference intervals and monitoring patients across laboratories - findings from a likely commutable external quality assurance program

OBJECTIVES

Laboratory results are increasingly interpreted against common reference intervals (CRIs), published clinical decision limits, or previous results for the same patient performed at different laboratories. However, there are no established systems to determine whether current analytical performance justifies these interpretations. We analysed data from a likely commutable external quality assurance program (EQA) to assess these interpretations.

METHODS

The use of CRIs was assessed by evaluating instrument group medians against minimum specifications for bias. The use of clinical decision limits was assessed using specifications from professional bodies, and the monitoring of patients by testing at different laboratories was assessed by comparing all-laboratory imprecision to within-subject biological variation.

RESULTS

Five of the 18 analytes with Australasian CRIs did not meet specification for all instrument groups. Among these, calcium and magnesium failed for one instrument group out of seven, while bicarbonate, chloride, and lipase failed for two instrument groups. Of the 18 analytes reviewed currently without CRIs in Australasia, 10 candidates were identified. Among analytes with clinical decision limits, i.e. lipids, glucose, and vitamin D, only triglycerides met both bias and imprecision specifications, while vitamin D met the imprecision specification. Monitoring patients by testing at different laboratories was supported for 15 of the 46 (33 %) analyte-method principles groups that met minimum imprecision specifications.

CONCLUSIONS

Analysis of data from commutable EQA programs can provide a mechanism for monitoring whether analytical performance justifies the interpretations made in contemporary laboratory practice. EQA providers should establish systems for routinely providing this information to the laboratory community.

Reference intervals: past, present, and future

Clinical laboratory test results alone are of little value in diagnosing, treating, and monitoring health conditions; as such, a clinically actionable cutoff or reference interval is required to provide context for result interpretation. Healthcare practitioners base their diagnoses, follow-up treatments, and subsequent testing on these reference points. However, they may not be aware of inherent limitations related to the definition and derivation of reference intervals. Laboratorians are responsible for providing the reference intervals they report with results. Yet, the establishment and verification of reference intervals using conventional direct methods are complicated by resource constraints or unique patient demographics. To facilitate standardized reference interval best practices, multiple global scientific societies are actively drafting guidelines and seeking funding to promote these initiatives. Numerous national and international multicenter collaborations demonstrate the ability to leverage combined resources to conduct large reference interval studies by direct methods. However, not all demographics are equally accessible. Novel indirect methods are attractive solutions that utilize computational methods to define reference distributions and reference intervals from mixed data sets of pathologic and non-pathologic patient test results. In an effort to make reference intervals more accurate and personalized, individual-based reference intervals are shown to be more useful than population-based reference intervals in detecting clinically significant analyte changes in a patient that might otherwise go unrecognized when using wider, population-based reference intervals. Additionally, continuous reference intervals can provide more accurate ranges as compared to age-based partitions for individuals that are near the ends of the age partition. The advantages and disadvantages of different reference interval approaches as well as the advancement of non-conventional reference interval studies are discussed in this review.

The Magnesium Status and Suggested Reference Ranges of Plasma Magnesium, Calcium, and Calcium/Magnesium Ratio in Chinese Adults over 45 Years Old

Magnesium (Mg) is an essential nutrient that participates in various enzymatic reactions and regulates important biological functions. The distribution and reference ranges in China have not been reported in populations more than 45 years old. This study aimed to assess the magnesium status and determine the reference values of plasma Mg, Ca, and Ca/Mg ratios for China's population more than 45 years old. A total of 2101 people were randomly selected from the China Nutrition and Health surveillance (CNHS) (2015-2017), considering the regional types and monitoring points. Then, 337 healthy individuals were further selected by a series of strict inclusion criteria to explore the reference range. The plasma magnesium and calcium were tested by inductively coupled plasma mass spectrometry (ICP-MS). The suggested reference values for plasma Mg, Ca, and Ca/Mg ratios were 0.75-1.14 mmol/L, 2.17-3.64 mmol/L, and 2.36-3.66, respectively. Taking 0.75 mmol/L as the lower cut-off limit, the prevalence of Mg deficiency was 6.66%, and the average level of plasma magnesium was 0.88 mmol/L for populations older than 45 years in China. In conclusion, this study provides the magnesium status and reference ranges for plasma Mg, Ca, and Ca/Mg ratio for Chinese people over 45 years old. The results of the recommended reference ranges in this study were very similar to our published results in women of reproductive age. Thus, the reference range of plasma magnesium in different populations in China was further improved.

Reference Curves for Pediatric Endocrinology: Leveraging Biomarker Z-Scores for Clinical Classifications

CONTEXT

Hormone reference intervals in pediatric endocrinology are traditionally partitioned by age and lack the framework for benchmarking individual blood test results as normalized z-scores and plotting sequential measurements onto a chart. Reference curve modeling is applicable to endocrine variables and represents a standardized method to account for variation with gender and age.

OBJECTIVE

We aimed to establish gender-specific biomarker reference curves for clinical use and benchmark associations between hormones, pubertal phenotype, and body mass index (BMI).

METHODS

Using cross-sectional population sample data from 2139 healthy Norwegian children and adolescents, we analyzed the pubertal status, ultrasound measures of glandular breast tissue (girls) and testicular volume (boys), BMI, and laboratory measurements of 17 clinical biomarkers modeled using the established "LMS" growth chart algorithm in R.

RESULTS

Reference curves for puberty hormones and pertinent biomarkers were modeled to adjust for age and gender. Z-score equivalents of biomarker levels and anthropometric measurements were compiled in a comprehensive beta coefficient matrix for each gender. Excerpted from this analysis and independently of age, BMI was positively associated with female glandular breast volume (β = 0.5, P < 0.001) and leptin (β = 0.6, P < 0.001), and inversely correlated with serum levels of sex hormone-binding globulin (SHBG) (β = -0.4, P < 0.001). Biomarker z-score profiles differed significantly between cohort subgroups stratified by puberty phenotype and BMI weight class.

CONCLUSION

Biomarker reference curves and corresponding z-scores provide an intuitive framework for clinical implementation in pediatric endocrinology and facilitate the application of machine learning classification and covariate precision medicine for pediatric patients.

Acceptance of a Nordic, Protein-Reduced Diet for Young Children during Complementary Feeding-A Randomized Controlled Trial

Early life is critical for developing healthy eating patterns. This study aimed to investigate the effects of a Nordic, protein-reduced complementary diet (ND) compared to a diet following the current Swedish dietary guidelines on eating patterns and food acceptance. At 4–6 months (mo) of age infants were randomized to a Nordic group (NG, n = 41) or a Conventional group (CG, n = 40), and followed until 18 mo of age. Daily intake of fruits and vegetables (mean ± sd) at 12 mo was significantly higher in the NG compared to the CG: 341 ± 108 g/day vs. 220 ± 76 g/day (p < 0.001), respectively. From 12 to 18 mo, fruit and vegetable intake decreased, but the NG still consumed 32% more compared to the CG: 254 ± 99 g/day vs. 193 ± 67 g/day (p = 0.004). To assess food acceptance, both groups were tested with home exposure meals at 12 and 18 mo. No group differences in acceptance were found. We find that a ND with parental education initiates healthy eating patterns during infancy, but that the exposure meal used in the present study was insufficient to detect major differences in food acceptance. This is most likely explained by the preparation of the meal. Nordic produce offers high environmental sustainability and favorable taste composition to establish healthy food preferences during this sensitive period of early life.

Reference intervals for 12 clinical laboratory tests in a Danish population: The Lolland-Falster Health Study

Reference intervals (RIs), developed as part of the Nordic Reference Interval Project 2000 (NORIP) are widely used in most European laboratories. We aimed to examine the validity of the NORIP RIs by establishing RIs for 12 frequently used laboratory tests based on data from a local Danish population and compare these local RIs with the NORIP RIs. Using an a posteriori direct sampling approach, blood sample data were assessed from 11,138 participants aged 18+ years in the Lolland-Falster Health Study (LOFUS), of whom 2154 turned out to meet criteria for being healthy for inclusion in establishing RIs according to the NORIP methodology. The 2.5th and 97.5th percentiles were calculated for alanine aminotransferase (ALAT), albumin, alkaline phosphatase, bilirubin, creatinine, hemoglobin, high-density lipoprotein cholesterol, iron, low-density lipoprotein cholesterol, thrombocytes, total cholesterol, and triglycerides. When comparing our estimates with the NORIP, the lower reference limits (RLs) for bilirubin and iron were lower, and higher for ALAT, thrombocytes and triglycerides. Upper RLs were lower for albumin (males and females ≥70 years), bilirubin and iron, but higher for alkaline phosphatase, triglycerides and for creatinine in men. In LOFUS, approximately 20% of the participants were healthy and qualified for inclusion in the establishment of RIs. Several of the local RIs differed from the NORIP RIs.

Protein-Reduced Complementary Foods Based on Nordic Ingredients Combined with Systematic Introduction of Taste Portions Increase Intake of Fruits and Vegetables in 9 Month Old Infants: A Randomised Controlled Trial

Abstract: Fruits and vegetables are healthy foods but under-consumed among infants and children. Approaches to increase their intake are urgently needed. This study investigated the effects of a systematic introduction of taste portions and a novel protein-reduced complementary diet based on Nordic foods on fruit and vegetable intake, growth and iron status to 9 months of age. Healthy, term infants (n = 250) were recruited and randomly allocated to either a Nordic diet group (NG) or a conventional diet group (CG). Infants were solely breast- or formula-fed at study start. From 4 to 6 months of age, the NG followed a systematic taste portions schedule consisting of home-made purées of Nordic produce for 24 days. Subsequently, the NG was supplied with baby food products and recipes of homemade baby foods based on Nordic ingredients but with reduced protein content compared to the CG. The CG was advised to follow current Swedish recommendations on complementary foods. A total of 232 participants (93%) completed the study. The NG had significantly higher intake of fruits and vegetables than the CG at 9 months of age; 225 ± 109 g/day vs. 156 ± 77 g/day (p < 0.001), respectively. Energy intake was similar, but protein intake was significantly lower in the NG (-26%, p < 0.001) compared to the CG. This lower protein intake was compensated for by higher intake of carbohydrate from fruits and vegetables. No significant group differences in growth or iron status were observed. The intervention resulted in significantly higher consumption of fruits and vegetables in infants introduced to complementary foods based on Nordic ingredients.

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

Background

Creatinine measurement for estimation of glomerular filtration rate (GFR) is a frequently used laboratory test. Differences in analytic creatinine methods have caused large inter-laboratory variation. International and national standardization efforts have been made in the last decade.

Methods

This study describes the results of the standardization efforts in Sweden by summarizing data for creatinine concentration in blood plasma in the Equalis quality assessment program during 1996–2014.

Results

Non-compensated Jaffe methods dominated in 1996–2001 (91 of 103 laboratories; 90%) and were then gradually replaced by either compensated Jaffe methods or enzymatic creatinine methods. In 2014 a majority of Swedish hospital laboratories (139 of 159; 87%) used enzymatic methods. The reported mean creatinine value by the Swedish laboratories was about 10 μmol/L higher than the isotope dilution mass spectrometry (IDMS) assured reference value in 2003, but consistent with the reference value from 2009 to 2014. The inter-laboratory CV was 7%–9% for creatinine values until 2007, and thereafter gradually decreased to about 4%–5% in 2014.

Conclusions

The introduction of enzymatic methods in Swedish laboratories has contributed to achieving a low inter-laboratory variation. Also, the reported values are lower for enzymatic methods compared to Jaffe methods, and the values obtained with enzymatic methods were consistent with IDMS certified values established at reference laboratories. Thus, many Swedish hospital laboratories reported 10 μmol/L lower, and more true, creatinine concentrations in 2012 than in 2003, which may cause bias in longitudinal studies.

Status on fasting definition for blood sampling in the Nordic countries - time for a harmonized definition

The preanalytical phase contains a vast number of practices whose variation may influence the results of laboratory testing and should, therefore, be standardized. The Working Group on Preanalytical Phase of the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM WG-PA) has suggested a standardization of venous blood specimen collection (VBSC) requirements for fasting samples including 12 h fasting time and water ad lib in the morning prior to specimen collection. The Nordic Scientific Preanalytical Working Group investigated the fasting definitions used in the Nordic countries. The Internet was assessed for stated fasting definitions of official organizations, larger laboratories, or laboratory groups. Fasting instructions for VBSC generally demanded patients to abstain from alcohol a day prior to, and to abstain from coffee, tea, smoking, and snuff intake in the morning of VBSC. Norway had a national fasting definition. Required fasting times varied from 8 to 14 h. The amount of water allowed in the morning of VBSC varied from ad lib to half a glass of water. The list of analytes, where fasting was required, held 9-15 analytes except for Finland with 65 analytes. Implementation of the EFLM WG-PRE standardization of VBSC requirements for fasting samples would decrease preanalytical variability and be beneficial for medical decisions and patient data comparison. We suggest the laboratories in the Nordic countries to implement the suggested fasting requirements, which are in line with those used when fasting reference intervals were established in the Nordic reference interval project.

Mode of oral iron administration and the amount of iron habitually consumed do not affect iron absorption, systemic iron utilisation or zinc absorption in iron-sufficient infants: a randomised trial

Different metabolic pathways of supplemental and fortification Fe, or inhibition of Zn absorption by Fe, may explain adverse effects of supplemental Fe in Fe-sufficient infants. We determined whether the mode of oral Fe administration or the amount habitually consumed affects Fe absorption and systemic Fe utilisation in infants, and assessed the effects of these interventions on Zn absorption, Fe and Zn status, and growth. Fe-sufficient 6-month-old infants (n 72) were randomly assigned to receive 6·6 mg Fe/d from a high-Fe formula, 1·3 mg Fe/d from a low-Fe formula or 6·6 mg Fe/d from Fe drops and a formula with no added Fe for 45 d. Fractional Fe absorption, Fe utilisation and fractional Zn absorption were measured with oral (57Fe and 67Zn) and intravenous (58Fe and 70Zn) isotopes. Fe and Zn status, infection and growth were measured. At 45 d, Hb was 6·3 g/l higher in the high-Fe formula group compared with the Fe drops group, whereas serum ferritin was 34 and 35 % higher, respectively, and serum transferrin 0·1 g/l lower in the high-Fe formula and Fe drops groups compared with the low-Fe formula group (all P<0·05). No intervention effects were observed on Fe absorption, Fe utilisation, Zn absorption, other Fe status indices, plasma Zn or growth. We concluded that neither supplemental or fortification Fe nor the amount of Fe habitually consumed altered Fe absorption, Fe utilisation, Zn absorption, Zn status or growth in Fe-sufficient infants. Consumption of low-Fe formula as the only source of Fe was insufficient to maintain Fe stores.

Creatine kinase in the U.S. population: Impact of demographics, comorbidities, and body composition on the normal range

BACKGROUND

Creatine kinase (CK) values are a critical part of the workup of suspected myopathies and are often assessed in patients that develop myalgia on statin therapy. CK elevations may influence the initiation and cessation of statin treatment, and incidentally discovered CK elevation may lead to further testing. A number of factors influence CK levels in healthy patients, but current reference ranges do not incorporate important influencers of CK such as race. Objectives of this study were to evaluate clinical factors associated with CK among healthy individuals and to develop practical reference ranges for important subgroups to improve test interpretation.

METHODS

CK was evaluated in nonpregnant participants ≥20 years old from the cross-sectional National Health and Nutrition Examination Survey (NHANES) 2011-2014. Linear and logistic regression stratified by sex identified clinical factors associated with CK levels. Adjustment for anthropomorphic measures assessed whether age and race-ethnicity differences in CK were explained by differences in body composition. The 95th and 97.5th percentiles of CK in sex/race-ethnicity subgroups were calculated, excluding patients with recent strenuous exercise.

RESULTS

A total of 10,096 nonpregnant adults were studied. Black race was strongly associated with CK. The odds ratio of having an abnormal CK for black women was 5.08 (95% CI 3.65-7.08) and for black men was 8.39 (95% CI 6.11-11.52). CK was substantially lower in older men. Differences in CK by age but not race-ethnicity were largely explained by body composition. Women with low body mass index were less likely to have an elevated CK, and overweight or obese men had an almost 2-fold greater odds of having an elevated CK. The 97.5th percentile of CK was 382 (95% CI 295-469) in white men, 1001 (95% CI 718-1284) in black men, 295 (95% CI 216-374) in white women, and 487 (95% CI 310-664) in black women.

CONCLUSION

CK is substantially higher in men and in black patients. Differences in body size and composition are also important but do not explain racial differences in CK. The 95th and 97.5th percentiles in sex and race-ethnicity subgroups provide a practical guide for clinicians interpreting CK values.

Standardization in laboratory medicine: Adoption of common reference intervals to the Croatian population

Considering the fact that the results of laboratory tests provide useful information about the state of health of patients, determination of reference value is considered an intrinsic part in the development of laboratory medicine. There are still huge differences in the analytical methods used as well as in the associated reference intervals which could consequently significantly affect the proper assessment of patient health. In a constant effort to increase the quality of patients’ care, there are numerous international initiatives for standardization and/or harmonization of laboratory diagnostics in order to achieve maximum comparability of laboratory test results and improve patient safety. Through the standardization and harmonization processes of analytical methods the ability to create unique reference intervals is achieved. Such reference intervals could be applied globally in all laboratories using methods traceable to the same reference measuring system and analysing the biological samples from the populations with similar socio-demographic and ethnic characteristics. In this review we outlined the results of the harmonization processes in Croatia in the field of population based reference intervals for clinically relevant blood and serum constituents which are in accordance with ongoing activity for worldwide standardization and harmonization based on traceability in laboratory medicine.

An unsupervised learning method to identify reference intervals from a clinical database

Reference intervals are critical for the interpretation of laboratory results. The development of reference intervals using traditional methods is time consuming and costly. An alternative approach, known as an a posteriori method, requires an expert to enumerate diagnoses and procedures that can affect the measurement of interest. We develop a method, LIMIT, to use laboratory test results from a clinical database to identify ICD9 codes that are associated with extreme laboratory results, thus automating the a posteriori method. LIMIT was developed using sodium serum levels, and validated using potassium serum levels, both tests for which harmonized reference intervals already exist. To test LIMIT, reference intervals for total hemoglobin in whole blood were learned, and were compared with the hemoglobin reference intervals found using an existing a posteriori approach. In addition, prescription of iron supplements were used to identify individuals whose hemoglobin levels were low enough for a clinician to choose to take action. This prescription data indicating clinical action was then used to estimate the validity of the hemoglobin reference interval sets. Results show that LIMIT produces usable reference intervals for sodium, potassium and hemoglobin laboratory tests. The hemoglobin intervals produced using the data driven approaches consistently had higher positive predictive value and specificity in predicting an iron supplement prescription than the existing intervals. LIMIT represents a fast and inexpensive solution for calculating reference intervals, and shows that it is possible to use laboratory results and coded diagnoses to learn laboratory test reference intervals from clinical data warehouses.

Stability of selected serum hormones and lipids after long-term storage in the Janus Serum Bank

BACKGROUND

The potential value of a biobank depends on the quality of the samples, i.e. how well they reflect the biological or biochemical state of the donors at the time of sampling. Documentation of sample quality has become a particularly important issue for researchers and users of biobank studies.

OBJECTIVE

The aim of this study was to investigate the long-term stability of selected components: cholesterol, high density cholesterol (HDLC), low density cholesterol (LDLC), apolipoprotein A1 (apo-A1), apolipoprotein B (apo B), follicle stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL), thyroid stimulating hormone (TSH) and free thyroxin (FT4).

DESIGN AND METHODS

Samples, stored at -25°C, from 520 men aged 40-49 years at blood sampling distributed in equally sized groups (n=130) according to length of storage, 0, 4, 17 and 29 years, respectively, were used in a cross sectional design. The freshly collected serum samples were used as a reference group to calculate storage related changes.

RESULTS

The differences between fresh samples and samples stored for 29 years were substantial for apo-A1 (+12%), apo-B (+22.3%), HDLC (-69.2%), LDLC (+31.3%), and PRL (-33.5%), while total cholesterol, FSH, LH, TSH and FT4 did not show any significant difference.

CONCLUSIONS

The study showed large differences in serum level of the selected components. The lipids and apolipoproteins were all changed except for total cholesterol. Most hormones investigated (FSH, LH, TSH and FT4) proved to be stable after 29 years of storage while PRL showed sign of degradation. The observed differences are probably due to long-term storage effects and/or external factors (i.e. diet and smoking).

The theory of reference values: an unfinished symphony

The history of the theory of reference values can be written as an unfinished symphony. The first movement, allegro con fuoco, played from 1960 to 1980: a mix of themes devoted to the study of biological variability (intra-, inter-individual, short- and long-term), preanalytical conditions, standardization of analytical methods, quality control, statistical tools for deriving reference limits, all of them complex variations developed on a central melody: the new concept of reference values that would replace the notion of normality whose definition was unclear. Additional contributions (multivariate reference values, use of reference limits from broad sets of patient data, drug interferences) conclude the movement on the variability of laboratory tests. The second movement, adagio, from 1980 to 2000, slowly develops and implements initial works. International and national recommendations were published by the IFCC-LM (International Federation of Clinical Chemistry and Laboratory Medicine) and scientific societies [French (SFBC), Spanish (SEQC), Scandinavian societies…]. Reference values are now topics of many textbooks and of several congresses, workshops, and round tables that are organized all over the world. Nowadays, reference values are part of current practice in all clinical laboratories, but not without difficulties, particularly for some laboratories to produce their own reference values and the unsuitability of the concept with respect to new technologies such as HPLC, GCMS, and PCR assays. Clinicians through consensus groups and practice guidelines have introduced their own tools, the decision limits, likelihood ratios and Reference Change Value (RCV), creating confusion among laboratorians and clinicians in substituting reference values and decision limits in laboratory reports. The rapid development of personalized medicine will eventually call for the use of individual reference values. The beginning of the second millennium is played allegro ma non-troppo from 2000 to 2012: the theory of reference values is back into fashion. The need to revise the concept is emerging. The manufacturers make a friendly pressure to facilitate the integration of Reference Intervals (RIs) in their technical documentation. Laboratorians are anxiously awaiting the solutions for what to do. The IFCC-LM creates Reference Intervals and Decision Limits Committee (C-RIDL) in 2005. Simultaneously, a joint working group IFCC-CLSI is created on the same topic. In 2008 the initial recommendations of IFCC-LM are revised and new guidelines are published by the Clinical and Laboratory Standards Institute (CLSI C28-A3). Fundamentals of the theory of reference values are not changed, but new avenues are explored: RIs transference, multicenter reference intervals, and a robust method for deriving RIs from small number of subjects. Concomitantly, other statistical methods are published such as bootstraps calculation and partitioning procedures. An alternative to recruiting healthy subjects proposes the use of biobanks conditional to the availability of controlled preanalytical conditions and of bioclinical data. The scope is also widening to include veterinary biology! During the early 2000s, several groups proposed the concept of 'Universal RIs' or 'Global RIs'. Still controversial, their applications await further investigations. The fourth movement, finale: beyond the methodological issues (statistical and analytical essentially), important questions remain unanswered. Do RIs intervene appropriately in medical decision-making? Are RIs really useful to the clinicians? Are evidence-based decision limits more appropriate? It should be appreciated that many laboratory tests represent a continuum that weakens the relevance of RIs. In addition, the boundaries between healthy and pathological states are shady areas influenced by many biological factors. In such a case the use of a single threshold is questionable. Wherever it will apply, individual reference values and reference change values have their place. A variation on an old theme! It is strange that in the period of personalized medicine (that is more stratified medicine), the concept of reference values which is based on stratification of homogeneous subgroups of healthy people could not be discussed and developed in conjunction with the stratification of sick patients. That is our message for the celebration of the 50th anniversary of Clinical Chemistry and Laboratory Medicine. Prospects are broad, enthusiasm is not lacking: much remains to be done, good luck for the new generations!

Reference intervals for parathyroid hormone for 70-year-old males and females: exclusion of individuals from the reference interval based on sex, calcium, diabetes, cardiovascular diseases or reduced kidney function has limited effects on the interval

Background

A problem when producing reference intervals for elderly individuals is that they often suffer from a number of diseases and they are most often on medication. If all such persons are excluded, there is a risk that the residual subgroup may not be representative of the population, we therefore wanted to compare the effects different exclusion criteria has on the reference intervals.

Methods

We measured parathyroid hormone (PTH), calcium, albumin and cystatin C in a cohort of 70-year-old males and females ( n = 1003). Reference intervals for PTH for males and females were calculated for the entire population and after exclusion of persons with calcium >2.60 mmol/L, calcium >2.51 mmol/L, diabetes, reduced glomerular filtration rate (GFR), and cardiovascular diseases.

Results

The calculated PTH reference interval 16 (CI 14–17) to 94 (CI 87–101) ng/L. Exclusion of study subjects resulted in smaller reference sample groups, but the reference limits remained within the 90% confidence intervals of the original reference limits. The selections thus had a very limited effect on the calculated reference interval for PTH.

Conclusions

Exclusion of elderly individuals with high calcium concentrations, diabetes, reduced GFR or cardiovascular disease has little effect on the reference interval for PTH. It is better not to exclude these individuals, as it will provide a broader base for the reference interval.

Serum bilirubin concentration in healthy adult North-Europeans is strictly controlled by the UGT1A1 TA-repeat variants

The major enzyme responsible for the glucuronidation of bilirubin is the uridine 5′-diphosphoglucose glucuronosyltransferase A1 (UGT1A1) enzyme, and genetic variation in the UGT1A1 gene is reported to influence the bilirubin concentration in the blood. In this study, we have investigated which gene-/haplotype variants may be useful for genetic testing of Gilbert's syndrome. Two groups of samples based on serum bilirubin concentrations were obtained from the Nordic Reference Interval Project Bio-bank and Database (NOBIDA): the 150 individuals with the highest bilirubin (>17.5 µmol/L) and the 150 individuals with normal bilirubin concentrations (<17.5 µmol/L). The individuals were examined for the TA₆>TA₇ variant in the UGT1A1 promoter and 7 tag-SNPs in an extended promoter region of UGT1A1 (haplotype analysis) and in selected SNPs in candidate genes (SLCO1B3, ABCC2 and NUP153). We found significant odds ratios for high bilirubin level for all the selected UGT1A1 variants. However, in stepwise multivariate logistic regression analysis of all genetic variants together with age, sex, country of origin and fasting time, the repeat variants of UGT1A1 TA₆>TA₇ and SLCO1B3 rs2117032 T>C were the only variants significantly associated with higher bilirubin concentrations. Most individuals with high bilirubin levels were homozygous for the TA₇-repeat (74%) while only 3% were homozygous for the TA₇-repeat in individuals with normal bilirubin levels. Among individuals heterozygous for the TA₇-repeat, a low frequent UGT1A1-diplotype harboring the rs7564935 G-variant was associated with higher bilirubin levels. In conclusion, our results demonstrate that in testing for Gilbert's syndrome, analyzing for the homozygous TA₇/TA₇-genotype would be appropriate.

Estimating reliable paediatric reference intervals in clinical chemistry and haematology

Very few high-quality studies on paediatric reference intervals for general clinical chemistry and haematology analytes have been performed. Three recent prospective community-based projects utilising blood samples from healthy children in Sweden, Denmark and Canada have substantially improved the situation.

CONCLUSION

The present review summarises current reference interval studies for common clinical chemistry and haematology analyses.

Reference values of thirty-one frequently used laboratory markers for 75-year-old males and females

BACKGROUND

We have previously reported reference values for common clinical chemistry tests in healthy 70-year-old males and females. We have now repeated this study 5 years later to establish reference values also at the age of 75. It is important to have adequate reference values for elderly patients as biological markers may change over time, and adequate reference values are essential for correct clinical decisions.

METHODS

We have investigated 31 frequently used laboratory markers in 75-year-old males (n = 354) and females (n = 373) without diabetes. The 2.5 and 97.5 percentiles for these markers were calculated according to the recommendations of the International Federation of Clinical Chemistry.

RESULTS

Reference values are reported for 75-year-old males and females for 31 frequently used laboratory markers.

CONCLUSION

There were minor differences between reference intervals calculated with and without individuals with cardiovascular diseases. Several of the reference intervals differed from Scandinavian reference intervals based on younger individuals (Nordic Reference Interval Project).

Effects of iron supplementation on serum hepcidin and serum erythropoietin in low-birth-weight infants

BACKGROUND

The iron-regulatory hormone hepcidin has not been studied in infants, who experience large physiologic changes in iron status.

OBJECTIVE

The objective was to study hepcidin and erythropoietin and their correlation with iron status in iron-replete and iron-deficient low-birth-weight (LBW) infants-a group at particular risk of iron deficiency (ID).

DESIGN

We randomly assigned 285 otherwise healthy LBW infants to receive, from 6 wk to 6 mo of age, 3 doses of iron supplements: 0 (placebo), 1, or 2 mg/kg daily. Hepcidin, erythropoietin, hemoglobin, and variables of iron status were analyzed.

RESULTS

Serum hepcidin did not change over time in the placebo group, despite a rapid decrease in serum ferritin. In iron-supplemented infants, hepcidin increased significantly, reaching a mean (±SD) concentration of 19.2 ± 2.5 ng/mL in the 2-mg/kg group compared with 13.0 ± 2.6 ng/mL in the placebo group at age 6 mo (P < 0.001). The difference was even larger between iron-deficient and iron-replete infants. Hepcidin was independently positively correlated with ferritin at all ages and was negatively correlated with the transferrin receptor concentration at age 6 wk and with transferrin at age 6 mo. Erythropoietin was initially similar between groups but decreased significantly in iron-supplemented infants. In addition to being negatively correlated with hemoglobin, it was also independently negatively correlated with indicators of iron status.

CONCLUSIONS

Hepcidin is closely associated with iron status and may be a useful indicator of iron stores and ID in infants. Erythropoietin is negatively correlated with iron status, which suggests a feedback mechanism that needs further study. This trial is registered at clinicaltrials.gov as NCT00558454.

Human epididymis protein 4 reference limits and natural variation in a Nordic reference population

The objectives of this study are to establish reference limits for human epididymis protein 4, HE4, and investigate factors influencing HE4 levels in healthy subjects. HE4 was measured in 1,591 samples from the Nordic Reference Interval Project Bio-bank and Database biobank, using the manual HE4 EIA (Fujirebio) for 802 samples and the Architect HE4 (Abbott) for 792 samples. Reference limits were calculated using the statistical software R. The influence of donor characteristics such as age, sex, body mass index, smoking habits, and creatinine on HE4 levels was investigated using a multivariate model. The study showed that age is the main determinant of HE4 in healthy subjects, corresponding to 2% higher HE4 levels at 30 years (compared to 20 years), 9% at 40 years, 20% at 50 years, 37% at 60 years, 63% at 70 years, and 101% at 80 years. HE4 levels are 29% higher in smokers than in nonsmokers. In conclusion, HE4 levels in healthy subjects are associated with age and smoking status. Age-dependent reference limits are suggested.

Evaluation of reference intervals for biomarkers sensitive to alcohol consumption, excess body weight and oxidative stress

BACKGROUND

Unexplained liver enzyme activities are often found in health screening programs and constitute an increasingly common cause for referral to specialized clinics. Recent studies have indicated that both excess body weight and alcohol consumption may lead to metabolic aberrations which are readily reflected in the activities of liver enzymes in circulation.

MATERIALS AND METHODS

We compared various laboratory markers and their upper normal limits in relation to information on alcohol consumption and BMI in a large population of apparently healthy individuals collected from Nordic countries.

RESULTS

Based on the data obtained from normal weight abstainers (BMI 19-25 kg/m(2)) the upper normal limits in men should be 50 U/L for ALT, and 45 U/L (<40 years) and 70 U/L (>or=40 years) for GGT, while the current recommendations are 70 U/L, 80 U/L, and 115 U/L, respectively. Already in comparisons between normal weight abstainers and corresponding moderate drinkers notable impacts (+14% - +74%) on upper limits for these analytes were seen, which further grew when adiposity occurred together with alcohol drinking (+75% - +186%, BMI >or=27 kg/m(2)). In addition to liver enzymes, similar changes were also found for uric acid.

CONCLUSIONS

Alcohol consumption and excess body weight even in apparently healthy individuals have a significant influence on liver enzyme activities, which may be due to a cumulative oxidative stress burden. The metabolic changes induced by adiposity or ethanol intake should be considered in the definition of normal ranges for all laboratory parameters sensitive to oxidative stress.

The liver in 30-year-old individuals with alpha(1)-antitrypsin deficiency

OBJECTIVE. Severe (PiZZ) alpha(1)-antitrypsin (AAT) deficiency is a risk factor for liver disease, i.e. juvenile cirrhosis in infancy, and cirrhosis and hepatoma in adulthood. Little is known about the risk of liver disease in individuals with moderate (PiSZ) AAT deficiency. To investigate the natural course of AAT deficiency, a cohort of PiZZ and PiSZ individuals identified by the Swedish National neonatal screening programme in 1972-74 is followed regularly. The aim of this study was to compare liver function in this cohort with healthy control subjects aged 30 years. MATERIAL AND METHODS. Blood samples were obtained from 89 PiZZ, 40 PiSZ, and 84 control subjects (PiMM), and plasma levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and gamma-glutamyl (GT) transpeptidase were analysed. RESULTS. The mean values of all liver enzymes were within the normal range in all Pi subgroups. However, the mean AST was higher in the PiZZ and PiSZ subgroups than in the PiMM subgroup (p < 0.001), and the mean ALT was higher in the PiZZ individuals than in the controls (p < 0.05), while GT did not differ significantly among the Pi subgroups. The PiZZ women taking oral contraceptives had higher mean AST and ALT (p < 0.01) and GT (p < 0.05) than the control women taking oral contraceptives. CONCLUSIONS. At the age of 30 years, PiZZ and PiSZ individuals have normal plasma levels of the transaminases AST and ALT, although they are significantly higher than those in healthy control subjects. Use of oral contraceptives seems to influence liver enzymes in PiZZ women.

Hematologic and serum biochemical reference intervals for free-ranging common bottlenose dolphins (Tursiops truncatus) and variation in the distributions of clinicopathologic values related to geographic sampling site

OBJECTIVE

To develop robust reference intervals for hematologic and serum biochemical variables by use of data derived from free-ranging bottlenose dolphins (Tursiops truncatus) and examine potential variation in distributions of clinicopathologic values related to sampling sites' geographic locations.

ANIMALS

255 free-ranging bottlenose dolphins.

PROCEDURES

Data from samples collected during multiple bottlenose dolphin capture-release projects conducted at 4 southeastern US coastal locations in 2000 through 2006 were combined to determine reference intervals for 52 clinicopathologic variables. A nonparametric bootstrap approach was applied to estimate 95th percentiles and associated 90% confidence intervals; the need for partitioning by length and sex classes was determined by testing for differences in estimated thresholds with a bootstrap method. When appropriate, quantile regression was used to determine continuous functions for 95th percentiles dependent on length. The proportion of out-of-range samples for all clinicopathologic measurements was examined for each geographic site, and multivariate ANOVA was applied to further explore variation in leukocyte subgroups.

RESULTS

A need for partitioning by length and sex classes was indicated for many clinicopathologic variables. For each geographic site, few significant deviations from expected number of out-of-range samples were detected. Although mean leukocyte counts did not vary among sites, differences in the mean counts for leukocyte subgroups were identified.

CONCLUSIONS AND CLINICAL RELEVANCE

Although differences in the centrality of distributions for some variables were detected, the 95th percentiles estimated from the pooled data were robust and applicable across geographic sites. The derived reference intervals provide critical information for conducting bottlenose dolphin population health studies.

Nordic Reference Interval Project Bio‐bank and Database (NOBIDA): a source for future estimation and retrospective evaluation of reference intervals

In the Nordic Reference Interval Project 2000 (NORIP) serum, Li-heparin plasma and EDTA buffy coat were collected at 102 laboratories in 5 Nordic countries from healthy individuals aged 18 years or more and evenly distributed for laboratory, gender and age. Multiple aliquots of these samples from each of about 3000 persons are now stored at the Nordic Reference Interval Project Bio-bank and Database (NOBIDA) at a temperature of below -80 degrees C. The commutable NFKK Reference Serum X with certified values traceable to reference methods and measured in NORIP in the same series as the samples is also available from NOBIDA. Data describing the person and the sample conditions are stored together with analytical results and data describing the measurement systems. The bio-bank along with material and data is administered by the NOBIDA committee on behalf of the NFKK (Scandinavian Society of Clinical Chemistry) to be used by Nordic laboratories for any purpose beneficial to the development of clinical biochemistry in general and particularly for creating reference intervals for other biochemical properties than those established by NORIP. Furthermore, research on the already stored information alone is encouraged. Thus colleagues are now welcome to use this extensive material for research and development in clinical biochemistry.

An improved indirect approach for determining reference limits from intra-laboratory data bases exemplified by concentrations of electrolytes / Ein verbesserter indirekter Ansatz zur Bestimmung von Referenzgrenzen mittels intra-laboratorieller Datensätze am Beispiel von Elektrolyt-Konzentrationen

Background: The current dogma of establishing intra-laboratory reference limits (RLs) and their periodical reviewing cannot be fulfilled by most laboratories due to the expenses involved. Thus, most laboratories adopt RLs from external sources often neglecting the problems of transferability. Presently accepted validation concepts still require experimental expenses. Several attempts were undertaken to derive RLs from the large data pools stored in modern laboratory information systems. Former indirect procedures were not generally accepted, but were recently further developed and combined with direct exclusion criteria and applied to estimate RLs of the catalytic activity concentrations of enzymes. This approach was now applied to several electrolytes in serum and plasma most commonly applied in clinical chemistry.

Methods: A smoothed kernel density function was estimated for the distribution of the mixed data of the sample group (combined data of non-diseased and diseased subjects). It was assumed that the “central” part of the distribution of all data represents the non-diseased (“healthy”) population (non-pathological values) with high probability. The central part was defined by truncation points using an optimisation method, and was used to estimate a Gaussian distribution of the values of non-diseased subjects. This distribution was now considered as the distribution of the non-diseased subgroup. The percentiles of this parametrical distribution were calculated to obtain unimodal reference intervals.

Results: The RLs obtained from different laboratories were similar to recently published values established by direct procedures. Stratification for gender was not necessary, but in some cases for age. With rising age, an increase of the upper RL and of the reference range was observed for potassium. Hospitalisation affected the RLs of sodium, potassium, calcium and magnesium, but not of phosphate. In the case of sodium, the data of at least five regional laboratories could be combined to common RLs. The presented indirect procedure was further validated with a large dataset of potassium concentrations from the NHANES III study with five groups of different health status.

Conclusions: The proposed strategy of combining exclusion criteria with an indirect method led to RLs from intra-laboratory data pools for electrolytes which were plausible in comparison to published data obtained by the generally accepted direct approach. The combined concept, however, still requires further investigations. Therefore, it is presently only recommended for checking and reviewing already existing RLs.

Whether western normative laboratory values used for clinical diagnosis are applicable to Indian population? An overview on reference interval

Reference Intervals denote normative values related to laboratory parameters/analytes used by diagnostic centers for clinical diagnosis. International guidelines recommend that every country must establish reference intervals for healthy individuals belonging to a group of homogeneous population. Considering enormous racial and ethnic diversity of Indian population, it is mandatory to establish reference intervals specific to Indian population. The overview on reference interval describes why the national organizations in India need to initiate nationwide efforts to establish its own laboratory standards for apparently healthy reference individuals belonging to our polygenetic, polyethnic, polyracial, multilinguistic and multicultural predominantly rural and appreciable urban Indian population with varied dietary habits.

Reference intervals: the way forward

New facts have recently enhanced interest in the topic of reference intervals. In particular, the International Organization for Standardization standard 15189, requesting that 'biological reference intervals shall be periodically reviewed', and the directive of the European Union on in vitro diagnostic medical devices asking manufacturers to provide detailed information on reference intervals, have renewed interest in the subject. This review presents an update on the topic, discussing the theoretical aspects and the most critical issues. The basic approach to the definition of reference intervals proposed in the original International Federation of Clinical Chemistry documents still remain valid. The use of data mining to obtain reference data from existing databases has severe limitations. New statistical approaches to discard outliers and to compute reference limits have been recommended. On the other hand, perspectives opened by the improvement in standardization through the implementation of the concept of traceability suggest new models to define 'common' reference intervals that can be transferred and adopted by different clinical laboratories in order to decrease the proliferation of different reference intervals not always justified by differences in population characteristics or in analytical methodology.

Serum nutrients and habitual dietary intake in colectomized FAP patients in Norway

BACKGROUND

Patients with familial adenomatous polyposis (FAP) are colectomized in young age in order to avoid development of colorectal cancer. Because colectomy radically changes gastrointestinal physiology, and food avoidance may be present, colectomized patients may be at risk for nutritional deficiency.

AIM OF THE STUDY

to evaluate: (1) serum biochemical levels as compared to reference; (2) dietary intake as compared to the recommendations.

METHODS

Blood samples, interviews and food frequency questionnaire were collected from 38 colectomized FAP patients with duodenal adenomas (mean age 40 years, range: 24-70). They were recruited from the Norwegian database on FAP.

RESULTS

Serum albumin was significantly higher (P < or = 0.0001), and Mg (P = 0.02), ferritin (P < or = 0.001), and cholesterol (P = 0.03) significantly lower, than reference levels. Compared to recommendations, a low intake was seen for folate and fiber (<50%), iron, thiamin, riboflavin (< 25%), and omega-3 fatty acids (8%). Sugar intake exceeded the recommendation, mainly due to a high intake of soft drinks. Food avoidance was reported by 53%.

CONCLUSIONS

We would suggest that the nutrient intake among FAP patients should at least meet the recommendations for healthy subjects. Their risk of metachronous cancers should also cause special attention to dietary factors that may prevent nutritional deficiency and carcinogenesis.

Sources of Variation of Commonly Measured Serum Analytes in 6 Asian Cities and Consideration of Common Reference Intervals

Background: In a previous study to determine the feasibility of common reference intervals in Asia, we found significant differences among populations from 6 cities. In this study, we attempted to define the sources of these differences.

Methods: We enrolled 580 healthy volunteers (279 men, 301 women, 20–62 years old), after a selection process that was based on the Clinical and Laboratory Standards Institute guidelines, and used a lifestyle questionnaire. All sera were obtained at a basal state and frozen at −80 °C until the collective assay was done. We measured 21 basic chemical analytes and 10 serum proteins.

Results: We used 3-level nested ANOVA to separate the variation (SD) into between-city (SD-city), between-sex (SD-sex), between-age (SD-age), and between-individual (SD-indiv) components. SD-indiv corresponds to one-quarter of the “pure” reference interval obtained after removing variations due to city, sex, and age. The SD-sex to SD-indiv ratio was &gt;0.8 for creatinine, urate, retinol-binding protein, and transthyretin. We observed high SD-city to SD-indiv ratios, ranging from 0.4 to 0.7, for 11 analytes including lactate dehydrogenase (LDH), electrolytes, IgG, and complement components and SD-age to SD-indiv ratios &gt;0.4 for LDH, alkaline phosphatase, and total cholesterol. Multiple regression analysis demonstrated several other relevant sources of variation, including body mass index, alcohol consumption, and cigarette smoking, although their contributions were generally smaller than those for sex, region, or age.

Conclusion: We observed unacceptably large regional differences in measured values of some analytes even after adjustment for age, sex, and lifestyle variables. Genetic and environmental factors may account for the residual differences.

Reference intervals for serum creatinine concentrations: assessment of available data for global application

BACKGROUND

Reference intervals for serum creatinine remain relevant despite the current emphasis on the use of the estimated glomerular filtration rate for assessing renal function. Many studies on creatinine reference values have been published in the last 20 years. Using criteria derived from published IFCC documents, we sought to identify universally applicable reference intervals for creatinine via a systematic review of the literature.

METHODS

Studies were selected for inclusion in the systematic review only if the following criteria were met: (a) reference individuals were selected using an "a priori" selection scheme, (b) preanalytical conditions were adequately described; (c) traceability of the produced results to the isotope dilution-mass spectrometry (IDMS) reference method was demonstrated experimentally, and (d) the collected data received adequate statistical treatment.

RESULTS

Of 37 reports dealing specifically with serum creatinine reference values, only 1 report with pediatric data and 5 reports with adult data met these criteria. The primary reason for exclusion of most papers was an inadequate demonstration of measurement traceability. Based on the data of the selected studies, we have collated recommended reference intervals for white adults and children.

CONCLUSION

Laboratories using methods producing traceable results to IDMS can apply the selected reference intervals for serum creatinine in evaluating white individuals.

An ELISA for apolipoprotein M reveals a strong correlation to total cholesterol in human plasma

Apolipoprotein M (apoM) is a 188 amino acid, 25 kDa protein belonging to the lipocalin protein superfamily. Although predominantly associated with high density lipoprotein, apoM is found in all major lipoprotein classes. To facilitate clinical studies of apoM, we have developed a sandwich ELISA for the measurement of apoM in human plasma. This method has been used to investigate normal apoM variation and to establish reference values for healthy individuals through the measurement of 598 samples from the Nordic Reference Interval Project Bio-bank and Database (NOBIDA) biobank. For women 18-49 years old, the reference interval for apoM was 0.58-1.18 micromol/l, whereas for women 50+ years and for men, the reference range was 0.61-1.30 micromol/l. Correlation studies of apoM with 26 common clinical chemical analytes from the NOBIDA database revealed a marked positive correlation with plasma total cholesterol (r = 0.52) and LDL and HDL cholesterol (r = 0.43 and 0.36, respectively). There was no statistically significant correlation with HDL/total cholesterol ratio or body mass index. In conclusion, a sandwich ELISA for the measurement of apoM in human plasma shows that apoM concentration is strongly correlated to total cholesterol in healthy individuals.

PHosphatidylethanol (PEth) concentrations in blood are correlated to reported alcohol intake in alcohol-dependent patients

AIMS

Phosphatidylethanol (PEth) is an abnormal phospholipid formed only in the presence of ethanol by the enzyme phospholipase D. PEth in blood is a promising new marker for ethanol abuse. None of the biological markers used at the present time is sensitive and specific enough for the diagnosis of alcoholism.

METHODS

The most frequently used alcohol markers [carbohydrate deficient transferrin (CDT), gamma-glutamyltransferase (GGT), and mean corpuscular volume (MCV)] were studied together with PEth in actively drinking alcohol-dependent patients (inpatients and outpatients), with regard to correlation to ethanol intake and diagnostic sensitivity of the markers. The relation between the markers was also studied.

RESULTS

PEth, CDT, and GGT correlated to ethanol intake, with the strongest correlation found for PEth. The diagnostic sensitivity for PEth was 99%, and for other markers it varied between 40 and 77%. Only when CDT was combined with GGT was a sensitivity of 94% reached. PEth correlated to CDT and GGT but not to MCV. CDT did not correlate to GGT or MCV.

CONCLUSIONS

Blood concentrations of PEth are highly correlated to ethanol intake, and the present results indicate that its diagnostic sensitivity is higher than that for previously established alcohol markers.

BN phenome: detailed characterization of the cardiovascular, renal, and pulmonary systems of the sequenced rat

The postgenome era has provided resources to link disease phenotypes to the genomic sequence, i.e., creating a disease "phenome." Our detailed characterization of the sequenced BN rat strain (BN/NHsdMcwi) provides the first concerted effort in creating a direct link between a sequenced genome and its resulting biology. For the BN sequence to be of broad value to investigators, these measures need to be put into the context of the spectrum of the laboratory rats, so that their physiology can be benchmarked against the sequenced BN. As a major step in generating a comprehensive cardiovascular and pulmonary disease phenome, we measured 281 traits related to diseases of the heart, lung, and blood (http://pga.mcw.edu) in the sequenced BN. We compared these data with those of the same traits measured across multiple genetic backgrounds, both genders, and differing environments. We show that no single strain, inbred or outbred, can be considered a physiological control strain; what is normal depends on what trait is being measured and the strains' genome backgrounds. We find vast differences between the genders, also dependent on genome background. By combining the values across all strains studied, we generated a "population" mean and normal range of values for each of these traits, which are more genetically representative than the measured values in any single inbred or outbred strain. These data provide a baseline for physiological comparison of traits related to cardiovascular, lung, blood, and renal function in the sequenced BN rats relative to the major strains of rats studied in biomedical research.