Reference intervals: the way forward

Verification of reference intervals in routine clinical laboratories: practical challenges and recommendations

Reference intervals (RIs) are fundamental tools used by healthcare and laboratory professionals to interpret patient laboratory test results, ideally enabling differentiation of healthy and unhealthy individuals. Under optimal conditions, a laboratory should perform its own RI study to establish RIs specific for its method and local population. However, the process of developing RIs is often beyond the capabilities of an individual laboratory due to the complex, expensive and time-consuming process to develop them. Therefore, a laboratory can alternatively verify RIs established by an external source. Common RIs can be established by large, multicenter studies and can subsequently be received by local laboratories using various verification procedures. The standard approach to verify RIs recommended by the Clinical Laboratory Standards Institute (CLSI) EP28-A3c guideline for routine clinical laboratories is to collect and analyze a minimum of 20 samples from healthy subjects from the local population. Alternatively, "data mining" techniques using large amounts of patient test results can be used to verify RIs, considering both the laboratory method and local population. Although procedures for verifying RIs in the literature and guidelines are clear in theory, gaps remain for the implementation of these procedures in routine clinical laboratories. Pediatric and geriatric age-groups also continue to pose additional challenges in respect of acquiring and verifying RIs. In this article, we review the current guidelines/approaches and challenges to RI verification and provide a practical guide for routine implementation in clinical laboratories.

Longitudinal Intra- and Inter-individual variation in T-cell subsets of HIV-infected and uninfected men participating in the LA Multi-Center AIDS Cohort Study

To assess the intra-individual and inter-individuals biological variation and the effect of aging on lymphocyte T-cells subsets.We assessed lymphocyte phenotypes (CD3, CD4, and CD8 T-cells) in 89 HIV-1-infected and 88 uninfected white non-Hispanic men every 6 months, to examine the biological variation for those measurements, and the average change in lymphocyte phenotype over 34 years.The markers showed significant intra-individuality in HIV-infected and uninfected individuals with index of individuality of <1.4. No mean changes were seen over the 34 years, with the exception of percentage CD4T-cells in HIV-uninfected individuals.In the pre-HAART era, HIV-infected individuals experienced an increase in mean absolute CD3 T-cell numbers (11.21 cells/μL, P = 0.02) and absolute CD8 T-cell numbers (34.57 cell/μl, P < .001), and in the percentage of CD8 T-cells (1.45%, P < .001) per year and a significant decrease in mean absolute CD4 T-cell numbers (23.68 cells/μl, P < .001) and in the percentage of CD4 T-cells (1.49%, P < .001) per year.In the post-HAART era, no changes in mean levels were observed in absolute CD3 T-cell count (P = .15) or percentage (P = .99). Significant decreases were seen in mean count (8.56 cells/μl, P < .001) and percentage (0.59%, P < .001) of CD8 T-cells, and increases in mean absolute count (10.72 cells/μl, P < .001) and percentage (0.47%, P < .001) of CD4 T-cells.With the exception of CD4 (%), no average changes per year were seen in lymphocyte phenotype of HIV-uninfected men. The results of coefficients of variation of intra and inter-individuals of this study can be useful for HIV-1 infection monitoring and in addition the observation could be a useful guide for intra- and inter-individual coefficient variations, and establishing quality goal studies of different blood biomarkers in healthy and other diseases.

A simple and robust liquid chromatography tandem mass spectrometry assay for determination of plasma free metanephrines and its application to routine clinical testing for diagnosis of pheochromocytoma

Plasma free metanephrines (PFMs) have high sensitivity for detecting pheochromocytoma (PCC). Herein, we developed a simple and reliable liquid chromatography tandem mass spectrometry assay for PFMs determination in Chinese population. PFMs were enriched by SPE without requiring extract evaporation or the use of buffers containing nonvolatile salts. The analytes were analyzed in multiple reaction monitoring mode. Inter- and intra-assay precisions were ≤4.3% and ≤ 6.3%. The lower limits of quantification were 0.07 nmol/L for metanephrine and 0.06 nmol/L for normetanephrine. Recoveries of PFMs were in the range of 89.3-113%. The method was free from significant matrix effect, carryover and interference. Owing to its fast analysis time, more than 150 samples/day could be easily performed by a single operator. With the established reference intervals of PFMs in the Chinese population, this simple and robust LC-MS/MS method could be valuable for use in routine clinical laboratories. It is noted that the combined tests of PFMs with urinary catecholamines or urinary vanillylmandelic acid could improve specificity.

Reference interval estimation of small sample sizes: A methodologic comparison using a computer-simulation study

BACKGROUND

According to the ASVCP and other guidelines, samples should comprise at least 120 individuals for reference interval (RI) estimation. Unfortunately, this minimum sample size is difficult to achieve in veterinary medicine. Several statistical methods are described to determine RIs from small sample sizes, but it is unclear which method provides the best accuracy.

OBJECTIVES

This study aimed to compare statistical strategies for estimating RIs and determine which strategy best enhances accuracy when the sample size is between 20 and 120.

METHODS

Different sample size groups (n = 120, 100, 80, 60, 40, and 20) were randomly selected 50 times from simulated Gaussian, log-normal, and left-skewed populations of 5000 total values. RIs were calculated using seven different statistical strategies comprising robust, parametric, nonparametric, and bootstrap methods, alone or in combination. RI accuracy was compared among these strategies at each sample size. The strategy that was significantly more accurate than others in the largest number of comparisons was considered as the one that best-enhanced RI accuracy.

RESULTS

The strategies that best-enhanced RI accuracy included using the parametric method when the Shapiro-Wilk P > 0.2 and, otherwise, using the nonparametric method to determine the upper and lower RI limits when there were between 60 and 100 reference individuals, and finding the lower RI limit when there were 40 reference individuals. The Box-Cox transformation parametric method best-enhanced RI accuracy of the upper RI limit when there were 40 reference individuals, and the nonparametric method best-enhanced RI accuracy of both RI limits when there were 20 reference individuals.

CONCLUSIONS

Using the parametric method when the Shapiro-Wilk P > 0.2, and the nonparametric method in other instances, will likely enhance RI accuracy when there are between 40 and 100 reference individuals. For smaller samples, the nonparametric method might be preferred.

Reference range determination for imaging biomarkers: Myocardial T1

BACKGROUND

Imaging biomarkers, such as the T₁ relaxation time of the myocardium using MRI, can be valuable in cardiac medicine if they are properly validated. Consensus statements recommend that for myocardial T₁ , each investigator should establish a reference range.

PURPOSE

To describe a statistically valid method for determining and reporting the reference range in each center, which simultaneously minimizes the twin risks of undersampling, leading to a uselessly uncertain range, and oversampling, which exposes volunteers to unnecessary scanning and wastes resources.

STUDY TYPE

Cohort.

POPULATION

In all, 278 normal human subjects without cardiac disease from two cardiac MR centers.

FIELD STRENGTH/SEQUENCE

1.5 T and 3 T; Modified Look-Locker Inversion recovery sequence.

ASSESSMENT

The T₁ relaxation time was estimated from multiple samples of tissue magnetization after inversion. A valid method for calculating a reference range was used.

STATISTICAL TESTS

Shapiro-Wilk test for normality; Tukey robust approach for identification of outliers; reference range calculation with confidence intervals.

RESULTS

Reference ranges for measurement of myocardial T₁ were calculated, with confidence intervals, enabling comparison with clinically important differences. At 3 T: 1129 to 1301 msec at site 1 (n = 21) and 1160 to 1309 msec at site 2 (n = 59), and at 1.5 T at site 2: 933 to 1020 msec (male, n = 130) and 965 to 1054 msec (female, n = 68). The 3 T reference range from site 1 was successfully benchmarked against the 3 T reference range at site 2.

DATA CONCLUSION

Myocardial T₁ reference ranges can be properly characterized, enabling clinical comparison to a valid reference range with known confidence intervals, using methodology similar to that described in this report.

LEVEL OF EVIDENCE

3 Technical Efficacy Stage: 3 J. Magn. Reson. Imaging 2019;50:771-778.

30-Year Longitudinal Study of Hematological Parameters of HIV-1 Negative Men Participating in Los Angeles Multicenter AIDS Cohort Study (MACS)

Background

Clinicians often use population-based reference intervals (RIs) when interpreting patient results. However, this method can present problems if the analyte in question has wide variability from person to person.

Methods

We examined the biological variation of routine hematologic markers in 82 white non-Hispanic men every 6 months during a 30-year period, to determine the usefulness of population-based RIs and age-related decline of hematological markers.

Results

Many of these markers showed significant person-to-person differences (index of individuality <1.4 in 10/11 markers) and change over time with a decrease in mean for white blood cells (WBCs), red blood cells (RBCs), hemoglobin, hematocrit, platelets, and neutrophils. The mean increased for monocytes, mean corpuscular volume (MCV), and mean corpuscular hemoglobin (MCH) (all P <.05).

Conclusion

Longitudinal analysis demonstrated significant decline in hematologic marker counts, with the exception of MCV and MCH. Establishment of a personalized baseline for hematologic assessments may be more useful to clinicians than previous methods.

Establishing Pediatric and Adult RBC Reference Intervals With NHANES Data Using Piecewise Regression

Objectives

To develop age- and sex-specific RBC reference intervals using the National Health and Nutrition Examination Survey (NHANES) 1999 to 2012, a large nationally representative, population-based, cross-sectional database (n = 44,328).

Methods

Comprehensive medical data were used to define a “healthy” population. Reference intervals for RBC count, hemoglobin, hematocrit, mean cell hemoglobin, mean cell hemoglobin concentration, mean cell volume, and red cell distribution width were computed using piecewise regression, an evidence-based statistical procedure that identifies breakpoints.

Results

The derived reference intervals were sex specific, unlike many current standards, and more precise for individuals of different ages, especially for children, adolescents, and elderly individuals, as additional breakpoints were detected for these groups. Suggested reference values for hematocrit and hemoglobin of older adult males were substantially lower than current values.

Conclusions

The reference intervals provided here, based on a large, nationally representative healthy population, contribute to the ongoing transition to precision medicine.

21-hydroxylase autoantibodies are more prevalent in Turner syndrome but without an association to the autoimmune polyendocrine syndrome type I

Turner syndrome (TS) is associated with an increased frequency of autoimmunity. Frequently observed autoimmune diseases in TS are also seen in the autoimmune polyendocrine syndrome type I (APS I), of which Addison disease is a key component. An overlapping antibody profile between TS and APS I could be considered. The aim of this work was to study women with TS regarding 21-hydroxylase (21-OH) antibodies and interferon omega (IFN-ω) antibodies, a highly specific marker for APS I, to determine if there are immunological overlaps between TS and APS I. Blood samples from 141 TS were assayed for 21-OH antibodies and IFN-ω antibodies using in-vitro-transcribed and translated autoantigen. Indices with a cut-off point of 57 and 200 for 21-OH antibody and IFN-ω antibody were used as reference. The median age of TS was 31·6 years (range = 11·2-62·2). Positive indices of 21-OH antibodies were present in six TS (4%), with a mean of 144·8 (range = 60-535). None had apparent adrenal insufficiency. There was no age difference comparing 21-OH antibody-positive TS (median age = 33·9 years, range = 17·7-44·7) and 21-OH antibody-negative TS (median age = 31·6 years, range = 11·2-62·2) (P = 0·8). No TS was positive for IFN-ω antibodies (mean = 42·4, range = -435-191). No overlapping autoimmune profile between TS and APS I was found. Autoimmunity against 21-OH among TS patients was more prevalent than previously identified, suggesting an increased risk of adrenal failure in TS. However, whether adrenal impairment will develop remains unknown.

Reference intervals for reticulocyte hemoglobin content in healthy infants

OBJECTIVES

Iron deficiency anemia in childhood is a serious public health problem worldwide. Reticulocyte hemoglobin content (Ret-He) is a novel biomarker of iron deficiency adopted for adults but there is a lack of reference intervals for Ret-He in infants. The aim of this study was to provide data from healthy infants.

METHODS

Swedish infants (n = 456), born at term after normal pregnancies were included. Ret-He was measured at birth (umbilical cord sample), 48-72 h, 4 months, and 12 months. Reference intervals were calculated as ±2 standard deviations from the mean of Ret-He.

RESULTS

Reference intervals for newborn Ret-He were 27.4 to 36.0 pg/L (N = 376) in the cord sample, 28.1-37.7 pg/L (N = 253) at 48-72 h, 25.6-33.4 pg/L (N = 341) at four months and 24.9-34.1 pg/L (N = 288) at 12 months. Ret-He was significantly lower among iron-deficient infants, at 4 months mean difference (95% CI) -4.2 pg/L (-6.1 to -2.4) and at 12 months mean difference (95% CI) -3.4 pg/L (-5.0 to -1.8).

CONCLUSIONS

This longitudinal study presents Ret-He reference intervals based on non-anemic and non-iron-deficient infants and constitutes a step towards standardizing Ret-He as a pre-anemia biomarker of iron deficiency in children.

Reference Intervals Generated by Electronic Medical Record Data Mining with Clinical Exclusions: Age-Specific Intervals for Thyroid-Stimulating Hormone from 33038 Euthyroid Patients

BACKGROUND

Serum thyroid-stimulating hormone (TSH) reference intervals are dependent on population characteristics, including prevalent thyroid disease and iodine status. Studies in the US have demonstrated increasing TSH levels with age, and the American Thyroid Association recommends higher TSH goals for older patients taking thyroid supplementation, but few laboratories offer age-specific reference intervals for TSH. Our objective was to establish TSH reference ranges in our racially diverse population in northern California.

METHODS

Data mining of electronic medical records was used with the a posteriori approach to select a euthyroid reference population for TSH reference intervals. A report gathered all TSH results from 2 weeks from >1 year in the past, excluding results from patients with thyroid-related disease or medication use at any time before or after the TSH test.

RESULTS

The reference population numbered 33038 and consisted of approximately 44% of the total TSH results reported in the selected time periods. The population identified as 46.5% white, 18.3% Asian, 17.0% Hispanic/Latino, 8.0% black/African American, and 10.3% other or unknown. These data demonstrate an increase in the median and 97.5 percentile of TSH levels with increasing age in adults. No clinically significant difference was seen between female and male individuals or between the self-identified races, except for lower TSH levels in the black/African American population.

CONCLUSIONS

The a posteriori approach using data mining for disease-specific criteria proved to be an efficient method for obtaining a large healthy reference population. Age-specific TSH reference ranges could prevent inappropriate diagnoses of subclinical hypothyroidism in older patients.

Reference intervals for serum progastrin-releasing peptide in healthy Chinese adults with electrochemiluminescence immunoassay

BACKGROUND

Reliable reference intervals for serum progastrin-releasing peptide (ProGRP) in healthy Chinese adults with electrochemiluminescence immunoassay (ECLIA) are still lacking in the Chinese population.

OBJECTIVES

The study aims to establish reference intervals for ProGRP with ECLIA in apparently healthy Chinese adults.

METHODS

A total of 384 apparently healthy individuals from six representative geographical regions in China were enrolled: 200 males and 184 females with a mean age of 43.4±12.2 years, and an age range from 21 to 85 years. Serum ProGRP levels were analyzed on Cobas e601 automatic immunoassay analyzer with ECLIA. Reference intervals for serum ProGRP with ECLIA were determined following CLSI C28-A3 guidelines using a nonparametric method.

RESULTS

In an apparently healthy Chinese population, the reference intervals for serum ProGRP with ECLIA were ⩽53.92 ng/L for adults aged 21-70 years and ⩽75.69 ng/L for adults aged >70 years, respectively.

CONCLUSIONS

The reference values for serum ProGRP with ECLIA in an apparently healthy Chinese population were established according to the CLSI C28-A3 document, providing a reference for the clinical work.

Short- and medium-term biological variation estimates of red blood cell and reticulocyte parameters in healthy subjects

Background:

The integrated evaluation of traditional and innovative red blood cell (RBC) and reticulocyte parameters is a rapid, inexpensive and non-invasive diagnostic tools for differential diagnosis and follow-up of anemia and other pathological conditions needing bone marrow erythropoiesis assessment. Therefore, estimating the biological variation (BV) of these parameters is essential for evaluating the analytical performance of hematological analyzers, and for enabling accurate data interpretation and appropriate clinical management. This study aims to define short- and medium-term BV estimates and reference change value (RCV) of RBC and reticulocyte parameters.

Methods:

Twenty-one healthy volunteers participated in the assessment of medium-term BV (blood sampling once/week, five consecutive weeks) and 22 volunteers in the assessment of short-term BV (blood sampling once/day, five consecutive days) using Sysmex XN. Outlier analysis was performed before CV-ANOVA, to determine BV estimates with confidence intervals (CI).

Results:

Medium- and short-term within-subject BV were between 0.3% and 16.4% and 0.2%–10.4% (MCH and IRF), respectively, whereas medium and short-term between-subjects BV ranged between 0.9% and 66.6% (MCHC and Micro-R) and 1.4%–43.6% (MCHC and IRF), respectively. The RCVs were similar for all parameters in both arms of the study, except for hemoglobin, RDW-CV and MCV.

Conclusions:

This study allowed for estimating the BV of many RBC and reticulocyte parameters, some of which have not been currently explored. For RBC, hemoglobin, RDW-CV and MCV it seems advisable to use RCV calculated according to monitoring time and/or differentiated by sex. As regards analytical goals, we suggest using the most stringent targets found in the short-term arm of this study.

Generating method-specific Reference Ranges - A harmonious outcome?

OBJECTIVES

When laboratory Reference Ranges (RR) do not reflect analytical methodology, result interpretation can cause misclassification of patients and inappropriate management. This can be mitigated by determining and implementing method-specific RRs, which was the main objective of this study.

DESIGN AND METHODS

Serum was obtained from healthy volunteers (Male + Female, n > 120) attending hospital health-check sessions during June and July 2011. Pseudo-anonymised aliquots were stored (at - 70 °C) prior t° analysis on Abbott ARCHITECT c16000 chemistry and i2000SR immunoassay analysers. Data were stratified by gender where appropriate. Outliers were excluded statistically (Tukey method) to generate non-parametric RRs (2.5th + 97.5th percentiles). RRs were compared to those quoted by Abbott and UK Pathology Harmony (PH) where possible. For 7 selected tests, RRs were verified using a data mining approach.

RESULTS

For chemistry tests (n = 23), Upper or Lower Reference Limits (LRL or URL) were > 20% different from Abbott ranges in 25% of tests (11% from PH ranges) but in 38% for immunoassay tests (n = 13). RRs (mmol/L) for sodium (138-144), potassium (3.8-4.9) and chloride (102-110) were considerably narrower than PH ranges (133-146, 3.5-5.0 and 95-108, respectively). The gender difference for ferritin (M: 29-441, F: 8-193 ng/mL) was more pronounced than reported by Abbott (M: 22-275, F: 5-204 ng/mL). Verification studies showed good agreement for chemistry tests (mean [SD] difference = 0.4% [1.2%]) but less so for immunoassay tests (27% [29%]), particularly for TSH (LRL).

CONCLUSION

Where resource permits, we advocate using method-specific RRs in preference to other sources, particularly where method bias and lack of standardisation limits RR transferability and harmonisation.

Indirect method for validating transference of reference intervals

Background:

Transference of reference intervals (RIs) from multicentre studies are often verified by use of a small number of samples from reference individuals or by the use of one serum sample (Serum X for NORIP RI). Despite recommended and appropriate methods, both have inconveniencies and drawbacks. Several attempts have been made to develop an indirect method, which uses historical data from the laboratory. These methods are retrospective relying on older test results. A near prospective method would be preferable for the laboratories introducing new methods or changing analytical platforms.

Methods:

We performed a data mining experiment using results from our laboratory information system covering patients from a large geographic area. Request patterns for patients with assumed healthy characteristics were identified and used to extract laboratory results for calculation of new RI by an indirect method. Calculated RI and confidence intervals (CIs) were compared to transferred NORIP RI verified by NFKK Reference Serum X.

Results:

We found that our indirect method and NFKK Reference Serum X in general produced similar results when verifying transference of RI. The method produces results for all stratifications. Only single stratifications and one analyte showed unexplained incongruences to the NORIP RI.

Conclusions:

Our results suggest using request patterns as a surrogate measure for good health status. This allows for a data mining method for validation of RI or validating their transference, which is likely to be applicable in countries with similar healthcare and laboratory information system.

Reference intervals for serum bilirubin, urea, and uric acid in healthy Chinese geriatric population

OBJECTIVES

The study aims to establish the reference intervals (RIs) for total bilirubin (TBIL), direct bilirubin (DBIL), urea (UR), and uric acid (UA) in healthy Chinese geriatric population.

METHODS

Eight hundred and twenty cases from six representative geographical regions in China (including male 413 cases and female 407 cases) of apparently healthy individuals aged 60-96 years were recruited. Serum TBIL, DBIL, UR, and UA were analyzed by automatic biochemical analyzer and RIs were determined following CLSI C28-A3 guidelines using a non-parametric method.

RESULTS

In apparently healthy Chinese geriatric population of China, the RIs of TBIL, DBIL, UR, and UA were 6.6~21.8 μmol/L, 1.9~8.0 μmol/L, 3.60~9.51 mmol/L, 179.2~460.9 μmol/L in males and 6.1~20.0 μmol/L, 1.8~7.1 μmol/L,3.35~8.89 mmol/L, 130.2~443.4 μmol/L in females, respectively.

CONCLUSIONS

The RIs of TBIL, DBIL, UR, and UA were established within apparently healthy geriatric Chinese population according to CLSIC28-A3 document, providing a reference for the clinical.

Simultaneous assay of cortisol and dexamethasone improved diagnostic accuracy of the dexamethasone suppression test

OBJECTIVES

The overnight dexamethasone (DXM) suppression test (DST) has high sensitivity, but moderate specificity, for diagnosing hypercortisolism. We have evaluated if simultaneous measurement of S-DXM may correct for variable DXM bioavailability and increase the diagnostic performance of DST, and if saliva (sa) is a feasible adjunct or alternative to serum.

DESIGN AND METHODS

Prospective study of DST was carried out in patients with suspected Cushing's syndrome (CS) (n = 49), incidentaloma (n = 152) and healthy controls (n = 101). Cortisol, cortisone and DXM were assayed by liquid chromatography-tandem mass spectrometry (LC-MS/MS).

RESULTS

Three hundred and two subjects underwent DST; S-cortisol was ≥50 nmol/L in 83 patients, of whom 11 had CS and 27 had autonomous cortisol secretion. The lower 2.5 percentile of S-DXM in subjects with negative DST (n = 208) was 3.3 nmol/L, which was selected as the DXM cut-off level. Nine patients had the combination of low S-DXM and positive DST. Of these, three had been misdiagnosed as having autonomous cortisol secretion. DST results were highly reproducible and confirmed in a replication cohort (n = 58). Patients with overt CS had significantly elevated post-DST sa-cortisol and sa-cortisone levels compared with controls; 23 of 25 with autonomous cortisol secretion had elevated sa-cortisone and 14 had elevated sa-cortisol.

CONCLUSIONS

Simultaneous measurement of serum DXM and cortisol reduced false-positive DSTs by 20% and improved the specificity. S-DXM >3.3 nmol/L is sufficient for the suppression of cortisol <50 nmol/L. Measurement of glucocorticoids in saliva is a non-invasive and easy procedure and post-DST sa-cortisone was found particularly useful in the diagnosis of CS.

Clinical laboratory reference values amongst children aged 4 weeks to 17 months in Kilifi, Kenya: A cross sectional observational study

Reference intervals for clinical laboratory parameters are important for assessing eligibility, toxicity grading and management of adverse events in clinical trials. Nonetheless, haematological and biochemical parameters used for clinical trials in sub-Saharan Africa are typically derived from industrialized countries, or from WHO references that are not region-specific. We set out to establish community reference values for haematological and biochemical parameters amongst children aged 4 weeks to 17 months in Kilifi, Kenya. We conducted a cross sectional study nested within phase II and III trials of RTS, S malaria vaccine candidate. We analysed 10 haematological and 2 biochemical parameters from 1,070 and 423 community children without illness prior to experimental vaccine administration. Statistical analysis followed Clinical and Laboratory Standards Institute EP28-A3c guidelines. 95% reference ranges and their respective 90% confidence intervals were determined using non-parametric methods. Findings were compared with published ranges from Tanzania, Europe and The United States. We determined the reference ranges within the following age partitions: 4 weeks to <6 months, 6 months to less than <12 months, and 12 months to 17 months for the haematological parameters; and 4 weeks to 17 months for the biochemical parameters. There were no gender differences for all haematological and biochemical parameters in all age groups. Hb, MCV and platelets 95% reference ranges in infants largely overlapped with those from United States or Europe, except for the lower limit for Hb, Hct and platelets (lower); and upper limit for platelets (higher) and haematocrit(lower). Community norms for common haematological and biochemical parameters differ from developed countries. This reaffirms the need in clinical trials for locally derived reference values to detect deviation from what is usual in typical children in low and middle income countries.

Biological variation of platelet parameters determined by the Sysmex XN hematology analyzer

BACKGROUND

This study was aimed to define the short- and medium-term biological variation (BV) estimates, the index of individuality and the reference change value (RCV) of platelet count, platelet distribution width, mean platelet volume, platelet larger cell ratio, plateletcrit and immature platelet fraction.

METHODS

The study population consisted of 43 health subjects, who participated to the assessment of medium-term (21 subjects; blood sampling once a week for 5 consecutive weeks) and short-term (22 subjects; blood sampling once a day for 5 consecutive days) BV study, using Sysmex XN-module. Eight subjects were also scheduled to participate to both phases. The data were subject to outlier analysis prior to CV-ANOVA, to determine the BV estimates with the relative confidence intervals.

RESULTS

The medium-term and short-term within-subject BV (CV_I) was comprised between 2.3 and 7.0% and 1.1-8.6%, whereas the medium-term and short-term between-subjects BV (CV_G) was comprised between 7.1 and 20.7% and 6.8-48.6%. The index of individuality and index of heterogeneity were always respectively <0.6 and >0.63 for all the parameters, in both arms of the study. The RCVs were similar for all parameters, in both arms of the study.

CONCLUSION

This study allowed to define the BV estimates of many platelet parameters, some of them unavailable in literature. The kinetics of platelet turnover suggests the use of short-term BV data for calculating analytical goals and RCV. The correct clinical interpretation of platelet parameters also necessitates that each laboratory estimates local RCV values.

Reference Values for the Revised Anti-Müllerian Hormone Generation II Assay: Infertile Population-based Study

Anti-Müllerian hormone (AMH) is now accepted as an important clinical marker of ovarian reserve and is increasingly measured as an initial evaluation at infertility clinics. The aim of this study was to establish reference values for the revised second generation (Gen II) assay using population-based data. In this population-based cohort study, AMH data from unselected infertile women aged 25-45 years from June 2013 to June 2014 (n = 15,801) were collected. The AMH values were measured using the revised Gen II assay. We established and validated 5 AMH-age regression models. Based on the optimal AMH-age model, reference values and centile charts were obtained. The quadratic model (log AMH = 0.410 × age -0.008 × age² -3.791) was the most appropriate for describing the age-dependent decrease in AMH measured using the revised Gen II assay. This is the largest population-based study to establish age-specific reference values of AMH using the revised Gen II assay. These reference values may provide more specific information regarding the ovarian reserve estimation of infertile women.

Laboratory reference intervals in the assessment of iron status in young children

OBJECTIVES

The primary objective was to establish reference intervals for laboratory tests used to assess iron status in young children using the Clinical and Laboratory Standards Institute guidelines. A secondary objective was to compare the lower limit of the reference interval with the currently recommended cut-off value for haemoglobin and serum ferritin in children 1-3 years of age.

METHODS

Blood samples were obtained from healthy children recruited during scheduled health supervision visits with their primary care physician. For our primary objective, outliers were removed; age partitions were selected and analysis of variance and pairwise comparisons were made between adjacent partitions; reference intervals and 90% CIs were calculated. For our secondary objective, we determined the proportion of children misclassified using the lower limit reference interval compared with the cut-off value.

RESULTS

Samples from 2305 male and 2029 female participants (10 days to 10.6 years) were used to calculate age and sex-specific reference intervals for laboratory tests of iron status. There were statistically significant differences between adjacent age partitions for most analytes. Approximately 10% of children 1-3 years of age were misclassified (underestimated) using the lower limit of the reference intervals rather than the currently recommended cut-off values for haemoglobin and serum ferritin.

IMPLICATIONS AND RELEVANCE

Clinical laboratories may consider adopting published paediatric reference intervals. Reference intervals may misclassify (underestimate) children with iron deficiency as compared with currently recommended cut-off values. Future research on decision limits derived from clinical studies of outcomes is a priority.

Reference intervals for common biochemistry laboratory tests in the Saudi population by a direct a priori method

BACKGROUND

Reference intervals (RI) for biochemistry laboratory tests are now based on Caucasian rather than Saudi populations. Test parameters may vary because of race, lifestyle, population structure and geographic location.

OBJECTIVES

To establish reference intervals for common clinical chemistry laboratory tests for the Saudi population.

DESIGN

Direct a priori method.

SETTING

Tertiary care hospital.

MATERIALS AND METHODS

Blood samples were taken from 625 individuals aged from 2 to 87 years from different geographic areas for 93 biochemistry tests. RIs were established following the International Federation of Clinical Chemistry guideline.

MAIN OUTCOME MEASURE(S)

Reference values for common biochemistry lab tests.

RESULTS

Ninety-three age- or gender-stratified reference intervals (RIs) based on the Saudi population were established. There were 72 non-partitioned tests. Most of the tests were similar to RIs from manufacturer's inserts. For some sex hormones (estrogen, luteinizing hormone, follicle-stimulating hormone, progesterone and 17 alpha-Hydroxyprogesterone) only male RIs were established as there were not enough samples to stratify for females based on physiologic status.

CONCLUSION

The RIs are reliable and applicable to a general Saudi population.

LIMITATIONS

Due to the sample size, RIs were not generated for some sex hormones for females.

A reference interval study for common biochemical analytes in Eastern Turkey: a comparison of a reference population with laboratory data mining

Introduction

The aim of this study was to define the reference intervals (RIs) in a Turkish population living in Northeast Turkey (Erzurum) for 34 analytes using direct and indirect methods. In the present study, the regional RIs obtained were compared with other RI studies, primarily the nationwide study performed in Turkey.

Materials and methods

For the direct method, 435 blood samples were collected from a healthy group of females (N = 218) and males (N = 217) aged between 18 and 65 years. The sera were analysed in Ataturk University hospital laboratory using Roche reagents and analysers for 34 analytes. The data from 1,366,948 records were used to calculate the indirect RIs using a modified Bhattacharya method.

Results

Significant gender-related differences were observed for 17 analytes. There were also some apparent differences between RIs derived from indirect and direct methods particularly in some analytes (e.g. gamma-glutamyltransferase, creatine kinase, LDL-cholesterol and iron). The RIs derived with the direct method for some, but not all, of the analytes were generally comparable with the RIs reported in the nationwide study and other previous studies in Turkey.There were large differences between RIs derived by the direct method and the expected values shown in the kit insert (e.g. aspartate aminotransferase, total-cholesterol, HDL-cholesterol, and vitamin B12).

Conclusions

These data provide region-specific RIs for 34 analytes determined by the direct and indirect methods. The observed differences in RIs between previous studies could be related to nutritional status and environmental factors.

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.

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.

Laboratory medicine in the new healthcare environment

The 21st century challenge is to redesign healthcare systems to be safe, efficient, effective, timely, equitable and patient-centred. Although laboratory medicine is integral to many of these objectives involving prevention, diagnosis, treatment, and managing disease of patients, it suffers from poor visibility as a medical discipline and as a profession and fewer rewards for educational efforts when compared to other medical disciplines. Laboratory scientists are often perceived as managing machinery and equipment, but conversely they need to take a position of shared clinical leadership, showing the role of laboratory tests to guarantee optimal care for patients. This is however challenging because of some reluctance by laboratory professionals to involve themselves in test structuring and requesting and in the inspection of work as it arrives because it is assumed that all requests are clinically necessary; there is a poor communication and integration between clinical wards and laboratory; and, importantly, there is the need for an excellent cultural and scientific background of laboratory professionals for implementing outcome research and to act as knowledge managers and skilled clinical consultants. By combining the unique talent of performing quality laboratory assays with knowledge of the pathophysiologic rationale behind the tests, laboratory professionals have the expertise to advise their clinical colleagues in regard to the appropriate test selection and interpretation of laboratory results, thereby creating opportunities to define the added value and the pivotal role of laboratory medicine on healthcare delivery.

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.

Complete blood count reference intervals and age- and sex-related trends of North China Han population

BACKGROUND

Defining common reference intervals (RIs) are encouraging. The aim of this study is to establish RIs for complete blood count (CBC) in a Chinese Han population and probe their age- and sex-related CBC trends. Additionally, we will compare the CBC RIs of Han with those of other races.

METHODS

In total 1259 Han individuals (584 male and 675 female) were recruited in North China. CBC was processed on Sysmex XE-2100, Coulter LH750 and Mindray BC5800 whose traceability was well verified. The non-parametric 2.5th-97.5th percentiles RIs were calculated.

RESULTS

The RIs for CBC parameters did not show apparent analyzer-specificity, apart from mean cellular volume (MCV), mean platelet volume (MPV), plateletcrit (PCT) and platelet distribution width (PDW). Red blood cell (RBC), hemoglobin (HBG), hematocrit (HCT), mean cellular hemoglobin (MCH), and mean cellular hemoglobin concentration (MGHC) are higher in males; and their male mean values tend to drop after 40 years; conversely, the female mean values tend to rise. Platelet (PLT) is higher in females and tends to drop after 40 years in both sexes. White blood cell (WBC) and absolute count of neutrophils (NE) and monocytes (MO) are higher in males, but there is no apparent change with age. Lymphocytes (LY) absolute count declines with age in males, but the same change in females is not obvious. RIs for HBG and HCT are similar among Han, Nordic, US European and US Mexican populations and are lower in US Africans. WBC RIs for Han and US African populations are lower than that for US Europeans and US Mexicans.

CONCLUSIONS

RIs for major blood cell parameters are not method-dependent; variations obviously exist in age, sex and race. Consequently, common RIs for most CBC parameters appear inapplicable.

Health assessment of free-ranging endangered Australian sea lion (Neophoca cinerea) pups: effect of haematophagous parasites on haematological parameters

Evaluation of the health status of free-ranging populations is important for understanding the impact of disease on individuals and on population demography and viability. In this study, haematological reference intervals were developed for free-ranging endangered Australian sea lion (Neophoca cinerea) pups within the context of endemic hookworm (Uncinaria sanguinis) infection and the effects of pathogen, host, and environment factors on the variability of haematological parameters were investigated. Uncinaria sanguinis was identified as an important agent of disease, with infection causing regenerative anaemia, hypoproteinaemia, and a predominantly lymphocytic-eosinophilic systemic inflammatory response. Conversely, the effects of sucking lice (Antarctophthirus microchir) were less apparent and infestation in pups appears unlikely to cause clinical impact. Overall, the effects of U. sanguinis, A. microchir, host factors (standard length, body condition, pup sex, moult status, and presence of lesions), and environment factors (capture-type and year of sampling) accounted for 26-65% of the total variance observed in haematological parameters. Importantly, this study demonstrated that anaemia in neonatal Australian sea lion pups is not solely a benign physiological response to host-environment changes, but largely reflects a significant pathological process. This impact of hookworm infection on pup health has potential implications for the development of foraging and diving behaviour, which would subsequently influence the independent survival of juveniles following weaning. The haematological reference intervals developed in this study can facilitate long-term health surveillance, which is critical for the early recognition of changes in disease impact and to inform conservation management.

A new robust statistical model for interpretation of differences in serial test results from an individual

Population-based reference intervals have very limited value for the interpretation of laboratory results when analytes display high biological individuality. In these cases, the longitudinal evaluation of individual results using the reference change value (RCV) is the recommended approach. However, the traditional model for RCV calculation requires a Gaussian frequency distribution of data and risks to overestimate the parameter if a correlation between within-subject serial measurements is present.

We propose and validate an alternative non-parametric statistical model for interpretation of differences in serial results from an individual, overcoming data distribution and correlation issues.

After describing the traditional and newly proposed statistical models, we compared them with each other using a simulation on three specific analytes displaying different concentration distributions in biological setting. We demonstrated that when analyte concentrations followed a Gaussian frequency distribution, as in the case of glycated hemoglobin, both methods can be used equally. On the contrary, if analyte concentrations present a bimodal (e.g., chromogranin A) or skewed (e.g., C-reactive protein) distribution, the information obtained by two statistical methods is different.

The proposed statistical approach may be more appropriate in assessing difference between serial measurements when individual data are not normally distributed.

Performance criteria for combined uncertainty budget in the implementation of metrological traceability

The measurement uncertainty budget should combine the uncertainty of higher order references, the uncertainty of commercial system calibration, the system imprecision and individual laboratory performance in terms of variability. Here we recommend that no more than one third of the total uncertainty budget, established by appropriate analytical performance specifications, is consumed by the uncertainty of references and approximately 50% of the total budget consumed by the manufacturer’s calibration and value transfer protocol. The remaining 50% should be available for the commercial system imprecision (including the batch to batch variation of the reagents) and individual laboratory performance in order to fulfil the uncertainty goal. For commercial systems to work properly, in vitro diagnostics (IVD) manufacturers will need to take more responsibility and ensure the traceability of the combination of platform, reagents, calibrators and control materials for system alignment verification that only as such (as a whole) are certified (“CE marked”) by the manufacturer itself in terms of traceability to the selected reference measurement system. Particularly, IVD manufacturers should report the combined (expanded) uncertainty associated with their calibrators when used in conjunction with other components of their analytical system (platform and reagents). This is more than what they are currently providing as traceability and uncertainty information.

ASVCP reference interval guidelines: determination of de novo reference intervals in veterinary species and other related topics

Reference intervals (RI) are an integral component of laboratory diagnostic testing and clinical decision-making and represent estimated distributions of reference values (RV) from healthy populations of comparable individuals. Because decisions to pursue diagnoses or initiate treatment are often based on values falling outside RI, the collection and analysis of RV should be approached with diligence. This report is a condensation of the ASVCP 2011 consensus guidelines for determination of de novo RI in veterinary species, which mirror the 2008 Clinical Laboratory and Standards Institute (CLSI) recommendations, but with language and examples specific to veterinary species. Newer topics include robust methods for calculating RI from small sample sizes and procedures for outlier detection adapted to data quality. Because collecting sufficient reference samples is challenging, this document also provides recommendations for determining multicenter RI and for transference and validation of RI from other sources (eg, manufacturers). Advice for use and interpretation of subject-based RI is included, as these RI are an alternative to population-based RI when sample size or inter-individual variation is high. Finally, generation of decision limits, which distinguish between populations according to a predefined query (eg, diseased or non-diseased), is described. Adoption of these guidelines by the entire veterinary community will improve communication and dissemination of expected clinical laboratory values in a variety of animal species and will provide a template for publications on RI. This and other reports from the Quality Assurance and Laboratory Standards (QALS) committee are intended to promote quality laboratory practices in laboratories serving both clinical and research veterinarians.

Reference intervals for plasma pro-gastrin releasing peptide (ProGRP) levels in healthy adults of Chinese Han ethnicity

OBJECTIVES

To determine the upper limits of the 95th percentile reference intervals (RIs) for the detection of the pro-gastrin releasing peptide (ProGRP) in plasma according to the Clinical and Laboratory Standards Institute (CLSI) C28-A3 guideline in a population of adult Chinese of Han ethnicity.

METHODS

Plasma samples were collected from 578 healthy adults. Plasma ProGRP values were measured by chemiluminescent microparticle immunoassay (CMIA) on Abbot ARCHITECT i2000 system analyzers.

RESULTS

Plasma ProGRP values did not conform to a Gaussian distribution, and thus non-parametric statistical methods were used to calculate RIs. Plasma ProGRP levels significantly increased with age, thus age-dependent RIs were determined. The upper limit of the 95th percentile RIs for plasma ProGRP was ≤57.26 pg/mL for young adults (18-50 years) and ≤81.42 pg/mL for old adults (&gt;50 years).

CONCLUSIONS

By CMIA, we established distinct age-dependent RIs for plasma ProGRP in healthy adults of Chinese Han ethnicity, thus generating a valuable reference for future clinical and laboratory studies.

The calculation of the cardiac troponin T 99th percentile of the reference population is affected by age, gender, and population selection: a multicenter study in Italy

BACKGROUND

The aim of this study is to determine the 99th upper-reference limit (URL) for cardiac troponin T (cTnT) in Italian apparently healthy subjects.

METHODS

The reference population was selected from 5 cities: Bolzano (n=290), Milano (CAMELIA-Study, n=287), Montignoso (MEHLP-Study, n=306), Pisa (n=182), and Reggio Calabria (MAREA-Study, n=535). Subjects having cardiac/systemic acute/chronic diseases were excluded. Participants to MEHLP project underwent cardiac imaging investigation. High-sensitive cTnT was measured with Cobas-e411 (Roche Diagnostics).

RESULTS

We enrolled 1600 healthy subjects [54.6% males; age range 10-90years; mean (SD): 36.4 (21.2) years], including 34.6% aged <20years, 54.5% between 20 and 64years, and 10.9% over 65years. In the youngest the 99th URL was 10.9ng/L in males and 6.8ng/L in females; in adults 23.2ng/L and 10.2ng/L; and in elderly 36.8ng/L and 28.6ng/L. After the exclusion of outliers the 99th URL values were significantly decreased (P<0.05) in particular those of the oldest (13.8ng/L and 14ng/L). MEHLP participants were divided in healthy and asymptomatic, according to known cardiovascular risk factors (HDL, LDL, glucose, C-reactive protein): the 99th URL of cTnT values of these subgroups was significantly different (19.5 vs. 22.7, P<0.05).

CONCLUSIONS

99th URL of cTnT values was strongly affected by age, gender, selection of subjects and the statistical evaluation of outliers.

B-cell subpopulations in children: National reference values

Peripheral B-lymphocytes undergo a series of changes during the first few years of life. Encounters with foreign antigens lead to maturation and differentiation. Several primary antibody deficiencies (PADs) affecting B-cell development are associated with abnormalities in the composition and/or differentiation of B-cell compartments. The most recent international classifications of primary immunodeficiencies (PIDs) and common variable immunodeficiencies (CVID) have highlighted the importance of B-cell immunophenotyping and age-specific reference intervals for diagnostic purposes. We established national reference values for memory B-cell subpopulations, on the basis of CD27 and surface IgD expression in the peripheral blood of 242 healthy children. We report here the absolute counts and percentages of naive, switched and non-switched memory B-cells for seven age groups, from neonates to adults. We found that the naive B-cells percentage declined between the ages of 6 months and 8 years, after which it remained stable at about 70–80%. Memory B-cells are already present at birth and their numbers increase throughout childhood, stabilizing between the ages of 12 and 18 years. The definition of reference intervals for pediatric B-cell levels should facilitate the screening and diagnosis of various B-cell immunodeficiencies. This multicenter study, providing national reference values, should thus facilitate immunological diagnosis in children.

Are commonly used paediatric reference intervals for water and electrolyte balance appropriate for clinical use?

BACKGROUND

Paediatric reference intervals are less well characterized than in adults. An initiative for harmonization of pathology across the United Kingdom has recommended an interval for sodium of 133-146 mmol/L at all ages.

METHODS

To assess the validity of this, the laboratory database was interrogated for all renal profiles (sodium, potassium, urea and creatinine) for children presenting to primary care over a 13-year period. While the primary interest was in sodium results, sufficient current data were also available for potassium and creatinine and so these were included for study. The electrolyte results were filtered to include only normal renal function and the remaining data were analysed for age-related differences.

RESULTS

Sodium concentrations were observed to be lower for infants (1-5 years of age) with a mean of 138 mmol/L, increasing towards adult concentrations (mean 140 mmol/L) by teenage years. A similar pattern was seen for potassium results, and creatinine was seen to increase with age. At all ages, the distributions of sodium concentrations measured in this population were observably tighter than the interval of 133-146 mmol/L recommended by Pathology Harmony.

CONCLUSIONS

We suggest that this interval is too wide, and more work is needed to establish more appropriate paediatric ranges.

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!

Verification of in vitro medical diagnostics (IVD) metrological traceability: responsibilities and strategies

To be accurate and equivalent, laboratory results should be traceable to higher-order references. Furthermore, their analytical performance should fulfill acceptable measurement uncertainty criteria defined to fit the intended clinical use. With this aim, In Vitro Diagnostics (IVD) manufacturers should define a calibration hierarchy to assign traceable values to their system calibrators and to fulfill during this process uncertainty limits for calibrators, which should represent a proportion of the uncertainty budget allowed for laboratory results. It is important that end-users may know and verify how manufacturers have implemented the traceability of their calibrators and estimated the corresponding uncertainty. However, full information about traceability and combined uncertainty of calibrators is currently not available. Important tools for IVD traceability surveillance are the verification by laboratories of the consistency of declared performance during daily operations performed in accordance with the manufacturer's instructions and the organization of appropriately structured External Quality Assessment (EQA) programs. The former activity should be accomplished by analyzing system control materials and confirming that current measurements are in the manufacturer's established control range. With regard to EQA, it is mandatory that target values for materials are assigned with reference procedures by accredited laboratories, that materials are commutable and that a clinically allowable inaccuracy for participant's results is defined.

Plasma-free vs deconjugated metanephrines for diagnosis of phaeochromocytoma

BACKGROUND

The diagnosis of phaeochromocytoma is commonly performed by the measurements of plasma-free normetanephrine and metanephrine. Plasma-deconjugated normetanephrine and metanephrine have been proposed as alternative, equivalent, but easier to measure biomarkers.

OBJECTIVE

The aim of this study was to compare the diagnostic performance of plasma-free vs deconjugated normetanephrine and metanephrine in patients tested for phaeochromocytoma.

METHODS

The study population included a reference group of 262 normotensive and hypertensive volunteers, 198 patients with phaeochromocytoma and 528 patients initially suspected of having the tumour, but with negative investigations after at least 2 years of follow-up. Measurements were performed using liquid chromatography with electrochemical detection.

RESULTS

Plasma concentrations of free normetanephrine were 17-fold higher in patients with phaeochromocytoma than in the reference population, a 72% larger (P < 0·001) difference than that for the 10-fold higher levels of plasma-deconjugated normetanephrine. In contrast, relative increases in plasma concentrations of free and deconjugated metanephrine were similar. Using upper cut-offs established in the reference population, measurements of plasma-free metabolites provided superior diagnostic performance than deconjugated metabolites according to measures of both sensitivity (97% vs 92%, P = 0·002) and specificity (93% vs 89%, P = 0·012). The area under the receiver operating characteristic curve for the free metabolites was larger than that for the deconjugated metabolites (0·986 vs 0·965, P < 0·001).

CONCLUSION

Measurements of plasma-free normetanephrine and metanephrine are superior to the deconjugated metabolites for diagnosis of phaeochromocytoma.

Harmonization in laboratory medicine: the complete picture

Evidence of the acute lack of interchangeable laboratory results and consensus in current practice among clinical laboratories has underpinned greater attention to standardization and harmonization projects. Although the focus is mainly on the standardization of measurement procedures, the scope of harmonization goes beyond method and analytical results: it includes all other aspects of laboratory testing, including terminology and units, report formats, reference intervals and decision limits, as well as test profiles and criteria for the interpretation of results. This review provides further insight on the issue of harmonization in laboratory medicine in view of the urgent need for a complete picture now that old and new drivers are calling for more effective efforts in this field. The main drivers for standardization and harmonization projects are first and foremost patient safety, but also the increasing trends towards consolidation and networking of clinical laboratories, accreditation programs, clinical governance, and advances in Information Technology (IT), including the electronic patient record. The harmonization process, which should be considered a three-tier approach involving local, national and international fronts, must go beyond the harmonization of methods and analytical results to include all other aspects of laboratory testing. A pertinent example of the importance of a complete picture in harmonization programs is given by the National Bone Health Alliance working in the field of bone turnover markers in cooperation with scientific societies including the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC).