The Asian project for collaborative derivation of reference intervals: (2) results of non-standardized analytes and transference of reference intervals to the participating laboratories on the basis of cross-comparison of test results

Derivation of sex and age-specific reference intervals for clinical chemistry analytes in healthy Ghanaian adults

OBJECTVIES

This study is aimed at establishing reference intervals (RIs) of 40 chemistry and immunochemistry analytes for Ghanaian adults based on internationally harmonized protocol by IFCC Committee on Reference Intervals and Decision Limits (C-RIDL).

METHODS

A total of 501 healthy volunteers aged ≥18 years were recruited from the northern and southern regions of Ghana. Blood samples were analyzed with Beckman-Coulter AU480 and Centaur-XP/Siemen auto-analyzers. Sources of variations of reference values (RVs) were evaluated by multiple regression analysis (MRA). The need for partitioning RVs by sex and age was guided by the SD ratio (SDR). The RI for each analyte was derived using parametric method with application of the latent abnormal values exclusion (LAVE) method.

RESULTS

Using SDR≥0.4 as threshold, RVs were partitioned by sex for most enzymes, creatinine, uric acid (UA), bilirubin, immunoglobulin-M. MRA revealed age and body mass index (BMI) as major source of variations of many analytes. LAVE lowered the upper limits of RIs for alanine/aspartate aminotransferase, γ-glutamyl transaminase and lipids. Exclusion of individuals with BMI≥30 further lowered the RIs for lipids and CRP. After standardization based on value-assigned serum panel provided by C-RIDL, Ghanaian RIs were found higher for creatine kinase, amylase, and lower for albumin and urea compared to other collaborating countries.

CONCLUSIONS

The LAVE effect on many clinical chemistry RIs supports the need for the secondary exclusion for reliable derivation of RIs. The differences in Ghanaian RIs compared to other countries underscore the importance of country specific-RIs for improved clinical decision making.

Reference intervals for Sysmex XN hematological parameters as assessed in the Dutch Lifelines cohort

OBJECTIVES

Our aim was to derive reference intervals for all Sysmex XN hematology analyzer parameters. The rationale behind the study was the lack of reference intervals for the XN analyzer cell population data (CPD) and functional parameters.

METHODS

Fresh fasting blood samples from 18,484 participants in the Dutch Lifelines study were analyzed using two automated XN analyzers. Structured health questionnaire data were used to select a subgroup of 15,803 apparently healthy individuals for inclusion in the reference population. The Latent Abnormal Values Exclusion (LAVE) approach was used to reduce the influence of latent diseases in the reference population on the resulting reference intervals. We applied analysis of variance to judge the need for partitioning of the reference intervals by sex or age.

RESULTS

We report reference intervals for 105 XN analyzer hematological parameters with and without applying LAVE. Sex-related partitioning was required for red blood cells, (RBC, RBC-O), hemoglobin (HGB, HGB-O), hematocrit (HCT), mean corpuscular hemoglobin concentration (MCHC), reticulocyte production index (RPI), and side scattered light intensity of the red blood cell population in the RET channel (RBC-Z). Partitioning for age was not warranted. Body mass index (BMI) and smoking had moderate influence on a minority of the parameters.

CONCLUSIONS

We provide reference intervals for all Sysmex XN analyzer routine, CPD and functional parameters, using a direct approach in a large cohort in the Netherlands.

Biological sources of variations of tartrate-resistant acid phosphatase 5b in a healthy Japanese population

BACKGROUND

Tartrate-resistant acid phosphatase 5b (TRACP5b) is a bone resorption marker that is mainly used in clinical management of osteoporosis. For proper interpretations of test results for serum TRACP5b, we explored their biological sources of variation, esp. age-related changes, and associations with other bone-related markers in healthy Japanese adults.

METHODS

During the 2009 East-Southeast Asian multicentre study for determination of reference intervals, 72 major laboratory tests were measured by centralized assays in 3541 well-defined healthy volunteers. The current study included 1980 test results in Japanese subjects for five bone-related markers: TRACP5b, bone alkaline phosphatase, intact parathyroid hormone, calcium and inorganic phosphate. Information on sources of variation, including body mass index, smoking habits and ABO-blood group, were obtained from a health status questionnaire.

RESULTS

Gender-specific profiles of age-related changes were observed for each parameter. Increased values starting from 40 years of age in females were most prominent for TRACP5b, followed by bone alkaline phosphatase and inorganic phosphate. TRACP5b in males decreased with body mass index, bone alkaline phosphatase and TRACP5b were higher in blood type-O subjects, especially in males. TRACPT5b was closely correlated with bone alkaline phosphatase, and moderately correlated with adjusted calcium and inorganic phosphate, especially in females aged ≥45 years. Reference intervals for each analyte were determined parametrically based on gender and age.

CONCLUSIONS

This study elucidated sources of variation of TRACP5b and related bone markers in healthy Japanese subjects and demonstrated a specific age profile for each marker. These results are of relevance for better clinical usage and interpretations of serum levels of bone markers.

Influence of ethnicity on biochemical markers of health and disease in the CALIPER cohort of healthy children and adolescents

Background Accurate pediatric reference intervals (RIs) for laboratory tests determined in a healthy pediatric population are essential for correct laboratory test interpretation and clinical decision-making. In pediatrics, RIs require partitioning by age and/or sex; however, the need for partitioning based on ethnicity is unclear. Here, we assessed the influence of ethnicity on biomarker concentrations in the Canadian Laboratory Initiative on Pediatric Reference Intervals (CALIPER) cohort of healthy children and adolescents and compared the results with the National Health and Nutrition Examination Survey (NHANES). Methods A total of 52 biomarkers were measured in a multiethnic population of 846-1179 healthy children (aged 5 to <19 years) upon informed consent. Biomarker concentrations were retrospectively compared between four major ethnic groups (i.e. Black, Caucasian, East Asian, and South Asian, determined by parental ethnicity). Retrospective results were verified prospectively using an additional 500 healthy pediatric samples with equal sample size across ethnicities. Ethnic-specific differences were assessed based on statistical significance and biological and analytical variations. Appropriate age-, sex-, and ethnic-specific RIs were calculated. Results Ethnic-specific differences were not observed for 34 biomarkers examined in the retrospective analysis, while 18 demonstrated statistically significant ethnic differences. Among these, seven analytes demonstrated ethnic-specific differences in the prospective analysis: vitamin D, amylase, ferritin, follicle-stimulating hormone (FSH), immunoglobulin A (IgA), immunoglobulin G (IgG), and immunoglobulin M (IgM). Analysis of select NHANES data confirmed CALIPER findings. Conclusions This is the first comprehensive Canadian pediatric study examining ethnic-specific differences in common biomarkers. While the majority of biomarkers did not require ethnic partitioning, ethnic-specific RIs were established for seven biomarkers showing marked differences. Further studies in other populations are needed to confirm our findings.

Establishment of reference intervals of clinical chemistry analytes for the adult population in Egypt

BACKGROUND

This is the first Egyptian nationwide study for derivation of reference intervals (RIs) for 34 major chemistry analytes. It was conducted as a part of the global initiative by the IFCC Committee on Reference Intervals and Decision Limits (C-RIDL) for establishing country-specific RIs based on a harmonized protocol.

METHODS

691 apparently healthy volunteers aged ≥18 years were recruited from multiple regions in Egypt. Serum specimens were analyzed in two centers. The harmonization and standardization of test results were achieved by measuring value-assigned serum panel provided by C-RIDL. The RIs were calculated by parametric method. Sources of variation of reference values (RVs) were evaluated by multiple regression analysis. The need for partitioning by sex, age, and region was judged primarily by standard deviation ratio (SDR).

RESULTS

Gender-specific RIs were required for six analytes including total bilirubin (TBil), aspartate and alanine aminotransferase (AST, ALT). Seven analytes required age-partitioning including glucose and low-density lipoprotein cholesterol (LDL-C). Regional differences were observed between northern and southern Egypt for direct bilirubin, glucose, and high-density-lipoprotein cholesterol (HDL-C) with all their RVs lower in southern Egypt. Compared with other collaborating countries, the features of Egyptian RVs were lower HDL-C and TBil and higher TG and C-reactive protein. In addition, BMI showed weak association with most of nutritional markers. These features were shared with two other Middle Eastern countries: Saudi Arabia and Turkey.

CONCLUSION

The standardized RIs established by this study can be used as common Egyptian RI, except for a few analytes that showed regional differences. Despite high prevalence of obesity among Egyptians, their RVs of nutritional markers are less sensitive to increased BMI, compared to other collaborating countries.

Sources of variation and establishment of Russian reference intervals for major hormones and tumor markers

OBJECTIVES

A multicenter study was organized to explore sources of variation (SVs) of reference values (RVs) for 22 major immunochemistry analytes and to determine reference intervals (RIs) for the Russian population.

METHODS

According to IFCC Committee on Reference Intervals and Decision Limits (C-RIDL) protocol, 758 healthy volunteers were recruited in St. Petersburg, Moscow, and Yekaterinburg. Serum samples were tested for five tumor markers, 17 hormones and related tests by Beckman Coulter's UniCel DxI 800 immunochemistry analyzer. SVs were explored using multiple regression analysis and ANOVA. Standard deviation ratio (SDR) of 0.4 was used as primary guide for partitioning RIs by gender and age.

RESULTS

SDR for between-city difference was <0.4 for all analytes. Secondary exclusion of individuals was done under the following conditions: for female sex-hormones, those with contraceptives (8%); for CA19-9, those supposed to have negative Lewis blood-group (10.5% males and 11.3% females); for insulin, those with BMI≥28 kg/m2 (31%); for the thyroid panel, those with anti-thyroid antibodies (10.3% males; 24.5% females), for CEA those with smoking habit (30% males and 16% females). Gender-specific RIs were required for all analytes except CA19-9, CA15-3, thyroid-related tests, parathyroid hormone, and insulin. Age-specific RIs were required for alpha-fetoprotein, CEA, all sex-hormones for females, FSH and progesterone for both sexes. RIs were generally derived by parametric method after Gaussian transformation using modified Box-Cox formula. Exceptions were growth hormone, estradiol for females in postmenopause, and progesterone for females in premenopause, for which nonparametric method was required due to bimodal distribution and/or insufficient detection limit.

CONCLUSION

RIs for major hormones and tumor markers specific for the Russian population were derived based on the up-to-date internationally harmonized protocol by careful consideration of analyte-specific SVs.

Establishing Ghanaian adult reference intervals for hematological parameters controlling for latent anemia and inflammation

Background

In Ghana, diagnostic laboratories rely on reference intervals (RIs) provided by manufacturers of laboratory analyzers which may not be appropriate. This study aimed to establish RIs for hematological parameters in adult Ghanaian population.

Methods

This cross‐sectional study recruited 501 apparently healthy adults from two major urban areas in Ghana based on the protocol by IFCC Committee for Reference Intervals and Decision Limits. Whole blood was tested for complete blood count (CBC) by Sysmex XN‐1000 analyzer, sera were tested for iron and ferritin by Beckman‐Coulter/AU480, for transferrin, vitamin‐B12, and folate was measured by Centaur‐XP/Siemen. Partitioning of reference values by sex and age was guided by “effect size” of between‐subgroup differences defined as standard deviation ratio (SDR) based on ANOVA. RIs were derived using parametric method with application of latent abnormal values exclusion method (LAVE), a multifaceted method of detecting subjects with abnormal results in related parameters.

Results

Using SDR ≥ 0.4 as a threshold, RIs were partitioned by sex for platelet, erythrocyte parameters except mean corpuscular constants, and iron markers. Application of LAVE had prominent effect on RIs for majority of erythrocyte and iron parameters. Global comparison of Ghanaian RIs revealed lower‐side shift of RIs for leukocyte and neutrophil counts, female hemoglobin and male platelet count, especially compared to non‐African countries.

Conclusion

The LAVE effect on many hematological RIs indicates the need for deliberate secondary exclusion for proper derivation of RIs. Obvious differences in Ghanaian RIs compared to other countries underscore the importance of country‐specific RIs for improved clinical decision‐making.

Determination of reference intervals for common chemistry and immunoassay tests for Kenyan adults based on an internationally harmonized protocol and up-to-date statistical methods

Background

Due to a lack of reliable reference intervals (RIs) for Kenya, we set out to determine RIs for 40 common chemistry and immunoassay tests as part of the IFCC global RI project.

Methods

Apparently healthy adults aged 18–65 years were recruited according to a harmonized protocol and samples analyzed using Beckman-Coulter analyzers. Value assigned serum panels were measured to standardize chemistry results. The need for partitioning reference values by sex and age was based on between-subgroup differences expressed as standard deviation ratio (SDR) or bias in lower or upper limits (LLs and ULs) of the RI. RIs were derived using a parametric method with/without latent abnormal value exclusion (LAVE).

Results

Sex-specific RIs were required for uric acid, creatinine, total bilirubin (TBil), total cholesterol (TC), ALT, AST, CK, GGT, transferrin, transferrin saturation (TfSat) and immunoglobulin-M. Age-specific RIs were required for glucose and triglyceride for both sexes, and for urea, magnesium, TC, HDL-cholesterol ratio, ALP, and ferritin for females. LAVE was effective in optimizing RIs for AST, ALT, GGT iron-markers and CRP by reducing influence of latent anemia and metabolic diseases. Thyroid profile RIs were derived after excluding volunteers with anti-thyroid antibodies. Kenyan RIs were comparable to those of other countries participating in the global study with a few exceptions such as higher ULs for TBil and CRP.

Conclusions

Kenyan RIs for major analytes were established using harmonized protocol from well-defined reference individuals. Standardized RIs for chemistry analytes can be shared across sub-Saharan African laboratories with similar ethnic and life-style profile.

Establishment of reference intervals for immunoassay analytes of adult population in Saudi Arabia

Background

This is a second part of report on the IFCC global multicenter study conducted in Saudi Arabia to derive reference intervals (RIs) for 20 immunoassay analytes including five tumor makers, five reproductive, seven other hormones and three vitamins.

Methods

A total of 826 apparently healthy individuals aged ≥18 years were recruited in three clinical laboratories located in western, central and eastern Saudi Arabia using the protocol specified for the global study. All serum specimens were measured using Abbott, Architect analyzers. Multiple regression analysis (MRA) was performed to explore sources of variation of each analyte: age, body mass index (BMI), physical exercise and smoking. The magnitude of variation of reference values (RVs) attributable to sex, age and region was calculated by ANOVA as a standard deviation ratio (SDR). RIs were derived by the parametric (P) method.

Results

MRA revealed that region, smoking and exercise were not relevant sources of variation for any analyte. Based on SDR and actual between-sex differences in upper limits (ULs), we chose to partition RIs by sex for all analytes except for α-fetoprotein and parathyroid hormone (PTH). Age-specific RIs were required in females for ferritin, estradiol, progesterone, testosterone, follitropin, luteotropin and prolactin (PRL). With prominent BMI-related increase, RIs for insulin and C-peptide were derived after excluding individuals with BMI > 32 kg/m2. Individuals taking vitamin D supplements were excluded in deriving RIs for vitamin D and PTH.

Conclusions

RIs of major immunoassay analytes specific for Saudi Arabians were established in careful consideration of various biological sources of variation.

A study on reference interval transference via linear regression

Background Reference intervals (RIs) transference can expand the applicability of established RIs. However, the study on transference methodology is insufficient, and RIs validation based on small samples cannot adequately identify transferred risk under complex situations. This study aimed to find appropriate conditions to ensure the effect of transference. Methods We established the RIs of Roche and Beckman systems for 27 analytes based on 681 healthy individuals. Roche RIs were converted into the Beckman RIs using linear regression (least squares method) which is divided into two methods - Methodref (500 test numbers with relatively narrow data range) and Methodep (80 test numbers with relatively wide data range). Taking the RIs established by Beckman results as standard, we assessed the accuracy, precision and trueness of transferred results under various conditions. Results A total of 29.6% and 48.1% of analytes were consistent between the two systems for the lower and upper reference limits, respectively. The concordance rates between transferred and measured RIs for Methodref were up to 74.1% and 92.6%, which were better than Methodep (44.4% and 59.3%). The CV of transferred reference limits decreased gradually with increasing test number under the same data range. For most analytes, excluding some electrolyte tests, we could obtain accurate results when r > 0.800 and the test number was sufficient regardless of the regression equation types. Conclusions Transferability of RIs is affected by many factors, such as correlation, test number, regression equation type, and quality requirement. To reduce the risk of transference, it is very important to select right method with reasonable conditions.

Distribution of serum amyloid A and establishment of reference intervals in healthy adults

Background

Serum amyloid A (SAA) plays a critical role in acute or chronic and is used in clinical laboratories as an indicator of inflammation. The elevated SAA is closely related to inflammation‐mediated diseases, such as liver diseases, autoimmune diseases, metabolism‐related diseases, amyloidosis, and tumors. However, there is no unified population reference interval for SAA. This study aimed to investigate the distribution of SAA in healthy Chinese adults 20‐79 years of age and to establish its population reference interval.

Methods

A total of 2365 healthy subjects met the requirements of this study. The levels of SAA were detected using an AU5821 automatic biochemical analyzer and its original reagents. According to the recommended methods of CLSI C28‐A3 and WS/T 402‐2012, the population reference interval of SAA was established using the unilateral 95th percentile (P₉₅), and the 90% confidence interval of upper limits was calculated.

Results

The distributions of SAA levels were not significantly different between sexes (P> .05) and also did not differ by age (P> .05). Therefore, the population reference interval for SAA was established as an upper limit of 11.0 mg/L (90% confidence interval: 9.3‐12.3 mg/L) by using the method of latex immunoturbidimetry.

Conclusions

Serum amyloid A is closely related to the occurrence and progression of various diseases. The preliminary establishment of a population reference interval for SAA can fully exert its potential clinical value.

Nationwide Multicenter Reference Interval Study for 28 Common Biochemical Analytes in China

A nationwide multicenter study was conducted in the China to explore sources of variation of reference values and establish reference intervals for 28 common biochemical analytes, as a part of the International Federation of Clinical Chemistry and Laboratory Medicine, Committee on Reference Intervals and Decision Limits (IFCC/C-RIDL) global study on reference values. A total of 3148 apparently healthy volunteers were recruited in 6 cities covering a wide area in China. Blood samples were tested in 2 central laboratories using Beckman Coulter AU5800 chemistry analyzers. Certified reference materials and value-assigned serum panel were used for standardization of test results. Multiple regression analysis was performed to explore sources of variation. Need for partition of reference intervals was evaluated based on 3-level nested ANOVA. After secondary exclusion using the latent abnormal values exclusion method, reference intervals were derived by a parametric method using the modified Box-Cox formula. Test results of 20 analytes were made traceable to reference measurement procedures. By the ANOVA, significant sex-related and age-related differences were observed in 12 and 12 analytes, respectively. A small regional difference was observed in the results for albumin, glucose, and sodium. Multiple regression analysis revealed BMI-related changes in results of 9 analytes for man and 6 for woman. Reference intervals of 28 analytes were computed with 17 analytes partitioned by sex and/or age. In conclusion, reference intervals of 28 common chemistry analytes applicable to Chinese Han population were established by use of the latest methodology. Reference intervals of 20 analytes traceable to reference measurement procedures can be used as common reference intervals, whereas others can be used as the assay system-specific reference intervals in China.

Reference intervals: current status, recent developments and future considerations

Reliable and accurate reference intervals (RIs) for laboratory analyses are an integral part of the process of correct interpretation of clinical laboratory test results. RIs given in laboratory reports have an important role in aiding the clinician in interpreting test results in reference to values for healthy populations. Since the 1980s, the International Federation of Clinical Chemistry (IFCC) has been proactive in establishing recommendations to clarify the true significance of the term 'RIs, to select the appropriate reference population and statistically analyse the data. The C28-A3 guideline published by the Clinical and Laboratory Standards Institute (CLSI) and IFCC is still the most widely-used source of reference in this area. In recent years, protocols additional to the Guideline have been published by the IFCC, Committee on Reference Intervals and Decision Limits (C-RIDL), including all details of multicenter studies on RIs to meet the requirements in this area. Multicentric RIs studies are the most important development in the area of RIs. Recently, the C-RIDL has performed many multicentric studies to obtain common RIs. Confusion of RIs and clinical decision limits (CDLs) remains an issue and pediatric and geriatric age groups are a significant problem. For future studies of RIs, the genetic effect would seem to be the most challenging area. 
The aim of the review is to present the current theory and practice of RIs, with special emphasis given to multicenter RIs studies, RIs studies for pediatric and geriatric age groups, clinical decision limits and partitioning by genetic effects on RIs.

Nationwide multicenter study aimed at the establishment of common reference intervals for standardized clinical laboratory tests in Japan

BACKGROUND

The Japanese Association of Medical Technologists (JAMT) sought to establish common reference intervals (RIs) applicable nationwide in Japan for 27 serum constituent analytes for which certified reference materials are available and nine analytes frequently measured in routine tests. More than 100 laboratories certified for metrological traceability collaborated in the recruitment, sampling, and measurement of analytes for the establishment of RIs. No previous attempt has been made to establish RIs by such a large number of laboratories. The allowable limits of trueness and intermediate precision based on the JAMT criteria were applied to the reference values measured by these laboratories, and measured values within the allowance limits were used to establish RIs.

METHODS

Reference individuals included 5748 healthy volunteers aged 18-65 years who were engaged in medical care-related work based on the CLSI guidelines. After secondary exclusion of individuals in whom abnormal values were detected in basic routine test items and adjustment for the distribution of age and gender, 3371 reference individuals were chosen in the parametric determination of RIs. Employing the three-level nested ANOVA, between-laboratory, -region, -sex, and -age variations were evaluated.

RESULTS

No significant difference was noted in between-region variations in any item. Results of ANOVA revealed between-sex and -age variations in 14 and 15 analytes, respectively. Based on these results of variation, RIs were established with and without partition by sex.

CONCLUSIONS

Since no between-region variation was detected in reference values among accuracy-certified core laboratories, RIs applicable nationwide were established.