Prerequisites for establishing common reference intervals.

Establishment of common reference intervals for homogeneous populations within regions is based on the same basic principles as the IFCC recommendations for individual laboratories, but a few additional prerequisites are needed. Thus, the need for common standardization and traceability during production of the reference values and with the application of the common reference intervals in the laboratories becomes crucial. Furthermore, the external control system must be geared to the purpose, using matrix-correct control materials with concentration values traceable to the same reference methods, and validation of results according to analytical quality specifications designed for the use of common reference intervals. Here, the standards may have a restrictive influence on the establishing of common reference intervals, with their demands for the use of the producers' traceability, instead of a relevant high-quality reference preparation shared by all the participants. Two main strategies for measurements are analysis immediately after the sampling, and storage of samples until analysis in one or a few analytical runs. The former strategy needs constant standardization and stability of the performance in many laboratories and in several analytical runs, resulting in between-run variation, whereas the latter precludes this between-run variation, but makes demands on the stability of the components under storage. When a considerable number of laboratories decide to establish common reference intervals, it is possible to obtain large sample sizes of reference values, which reduces the confidence intervals around the reference limits. It also makes it possible to collect samples from many subgroups, such as racial groups and groups related to different environmental conditions, as well as the traditional groupings according to age and gender, pregnancy and use of oestrogens. If all these subgroups are large, e.g. n>500, the confidence limits will be small and criteria for partitioning can be applied. Choosing reference individuals is not easy, as definitions of health, as well as rule-in and rule-out criteria vary from one investigation to the other. Therefore, the strategy and the criteria must be thoroughly described. Arguments for establishing common reference intervals are not needed. On the contrary, lack of such common reference intervals should be explained.

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

Each of 102 Nordic routine clinical biochemistry laboratories collected blood samples from at least 25 healthy reference individuals evenly distributed for gender and age, and analysed 25 of the most commonly requested serum/plasma components from each reference individual. A reference material (control) consisting of a fresh frozen liquid pool of serum with values traceable to reference methods (used as the project "calibrator" for non-enzymes to correct reference values) was analysed together with other serum pool controls in the same series as the project samples. Analytical data, method data and data describing the reference individuals were submitted to a central database for evaluation and calculation of reference intervals intended for common use in the Nordic countries. In parallel to the main project, measurements of commonly requested haematology properties on EDTA samples were also carried out, mainly by laboratories in Finland and Sweden. Aliquots from reference samples were submitted to storage in a central bio-bank for future establishment of reference intervals for other properties. The 25 components were, in alphabetical order: alanine transaminase, albumin, alkaline phosphatase, amylase, amylase pancreatic, aspartate transaminase, bilirubins, calcium, carbamide, cholesterol, creatine kinase, creatininium, gamma-glutamyltransferase, glucose, HDL-cholesterol, iron, iron binding capacity, lactate dehydrogenase, magnesium, phosphate, potassium, protein, sodium, triglyceride and urate.

Descriptive analytical data and consequences for calculation of common reference intervals in the Nordic Reference Interval Project 2000.

In the Nordic Reference Interval Project (NORIP), data from 102 Nordic clinical chemical laboratories were obtained. Each laboratory reported analytical data on up to 25 of the most commonly used clinical biochemical properties, including results from each of a minimum of 25 reference individuals. A reference material consisting of a liquid frozen pool of serum with values traceable to reference methods (used as the project "calibrator" for non-enzymes to correct reference values) was measured together with other serum pool controls in each laboratory in the same analytical series as the project samples. The data on the controls were used to evaluate the analytical quality of the routine methods. For reference interval calculations, only such reference values on enzymes were accepted that were obtained by applying the International Federation of Clinical Chemistry (IFCC) compatible methods (37 degrees C), while "calibrator"-corrected reference values were used in the cases of non-enzymes. For each property, gender- and age-specific reference intervals were estimated, based on simple non-parametric calculations and using objective criteria to perform partitioning into subgroups. It is concluded that the same reference intervals are applicable in all five Nordic countries. The following descriptive data for the considered properties are presented in the tables: number of measurement values from each country and measurement system, certified/indicative target values for controls, differences between methods and measurement systems together with coefficients of variation, effects of control correction on the measurement values, differences between subgroups as determined by age, gender, country and material, and comparison of the new reference intervals with those presented in standard textbooks. The 25 components involved in this project were (listed in alphabetical order): Alanine transaminase, albumin, alkaline phosphatase, amylase, amylase pancreatic type, aspartate transaminase, bilirubin, calcium, carbamide, cholesterol, creatine kinase, creatininium, gamma-glutamyltransferase, glucose, HDL-cholesterol, iron, iron-binding capacity, lactate dehydrogenase, magnesium, phosphate, potassium, protein, sodium, triglyceride and urate.

Reference individuals, blood collection, treatment of samples and descriptive data from the questionnaire in the Nordic Reference Interval Project 2000.

The rules for recruitment of reference individuals, inclusion and preparation of individuals, blood collection, treatment of samples (and control materials) and analysis at the 102 medical laboratories attending the Nordic Reference Interval Project (NORIP) are given as well as the rules for central exclusion of reference individuals. The individuals (18-91-year-olds) should be evenly distributed on age and gender groups. The 3002 reference individuals who contributed at least one reference value to the finally suggested reference intervals were characterized using the information in the questionnaire. Gender, age and country are the main entries in the tables. Other variables in the cross-tables or figure are height, weight, body mass index, ethnic origin, heredity for diabetes, chronic disease, oestrogens or oral contraceptives, other medication, hard physical activity, previous blood donations, smoking habits, use of alcohol, hours since last meal and time of blood collection (hour, day of week, month, year). The Danes had the highest alcohol consumption and the Icelanders had the highest body mass index. The information in this article may interest potential users of the Nordic Reference Interval Project bio-bank and database (NOBIDA) in which serum, Li-heparin plasma and EDTA buffy coat from the mentioned individuals are stored below -80 degrees C.

Effect of analytical quality on establishing common reference intervals and their use.

In the Nordic Reference Interval Project (NORIP), reference intervals were established for 25 common clinical biochemical quantities. In the project, samples from more than 3000 reference individuals collected in the 102 participating laboratories from all five Nordic countries were analysed locally. In order to maintain a high level of analytical quality and to document this quality, a common calibrator/reference preparation (CAL) and a number of control samples were analysed together with the reference samples. All these materials were serum pools of unprocessed serum from many donors in order to obtain commutable materials. The CAL was used to harmonize the many different analytical procedures and calibrations by simple recalibration by the factor T/M where T is the target value based on reference methods and M is the mean of 10 replicate measurements of CAL in each laboratory. The analytical quality specifications (analytical goals) were based on specifications created directly for the purpose of sharing common reference intervals and only the bias criteria were used because bias is the dominating problem in transfer of reference intervals. These specifications were different for the evaluation of reference values to create common reference intervals and for the laboratories to use these common reference intervals (when established). An interesting outcome was that it was only for the biologically well-regulated quantities serum-sodium and serum-calcium that the selection of the best laboratories gave considerably narrower reference intervals.

Measured muscle sodium content in biopsy specimens is a reflection of true intracellular content.

Determined on the basis of small skeletal muscle biopsies, muscle sodium content has a very high coefficient of variation. Furthermore, at least some of the measured sodium must originate from the extracellular space. In order to assess the applicability of the measurement of intracellular sodium on small muscle biopsy specimens, the measured sodium content was related to the content of dry solids in 25 muscle biopsy samples, and compared with the theoretical content of sodium with varying extra- and intracellular water content in biopsy samples. Four of the 25 measurements were clearly outliers. Disregarding these outliers, it was found that muscle sodium content varied with intracellular water content, whereas the theoretical effect of addition of extracellular water could not account for the observed values. The difference depended upon the specified conditions, but the slope of the theoretical regression line (-25.92 mmol x (kg dry weight)(-1) x %(-1), which was closest to the observed slope, -8.55 mmol x (kg dry weight)(-1) x %(-1), differed substantially (p < 0.0001). No association was found between the primarily intracellular ions muscle potassium and muscle magnesium on the one hand and either muscle sodium or muscle water content on the other. The measured sodium content in muscle biopsy specimens, which are freeze-dried and dissected, seems to reflect the true intracellular sodium content to some extent. The total content of sodium seems to be closely related to the content of water within the skeletal muscle cells.

Can capillary whole blood glucose and venous plasma glucose measurements be used interchangeably in diagnosis of diabetes mellitus?

According to new proposals from the American Diabetes Association (ADA) and WHO, venous peripheral plasma is the preferred system for measuring glucose for diagnosing diabetes mellitus. Owing to the instability of glucose in plasma after blood sampling, strict well-defined and standardized preanalytical conditions are essential to ensure that glucose concentration measured in plasma reflects real blood glucose in the patient. This is in contrast to the capillary whole blood measurements, which are easy to perform and well established. We investigated whether it is possible to perform analysis on capillary whole blood but express the results as plasma glucose values and hence obtain comparable results and the same predictive values for diagnosis in the individual patient? The conclusion of our investigations is that these two systems are not interchangeable and that conversion should not be done for diagnostic purposes where plasma determinations are recommended.

Upper reference limit, analytical quality specifications and clinical use of haemoglobin A1C.

Haemoglobin A1c (HbA1c) is now the key component for monitoring glycaemic control in diabetes mellitus (DM), especially for its close relation to diabetes complications. However, treatment goals in terms of HbA1c concentrations have been difficult to define and compare because of lack of international standardization and lack of common reference values of HbA1c concentrations. The aims of our study were to document our HbA1c analysis and make it traceable to international reference laboratories with the aid of current reference preparations, to establish a reference interval based on a low-risk population, and to evaluate the analytical quality specifications, which could meet clinical needs. The s(analytical) of our method (Tosoh) was < 0.3 HbA1c%, and the mean bias as estimated from Dr Cas Weykamp's reference preparation was below 0.3 HbA1c. This was the same as that for participating Scandinavian and international reference laboratories. The concentrations were made traceable to results from the Diabetes Control and Complication Trial (DCCT) and the UK Prospective Diabetes Study (UKPDS). Risk groups for DM were ruled out from a randomly selected population in Vejle County, which isolated a "low-risk" reference population. The 97.5 reference interval in this population (N=430) was from 5.07 HbA1c% (95% CI: 5.02-5.11) to 6.24 HbA1c% (95% CI: 6.19-6.30), and the 99.9 centile was 6.62 HbA1c% (95%) CI 6.55-6.71). Body mass index, age and gender contributed marginally to the level of HbA1c concentrations. A 10% delta risk estimate of DM complications was detectable with a probability of Type I error of 40%, while adoption of a significance level of 95% and consideration to biological variation needed a risk difference of at least 33% to be detected. The critical difference was 11% for changes in either direction at s(analytical) < or = 0.2 HbA1c% and a s(biological) of 0.3 HbA1c%. Based on criteria for sharing common reference intervals and clinical utility, we accepted that the bias and s(analytical) should both be < 0.3 HbA1c% at the level of 7.0 HbA1c%.

Reproducibility of S-insulin and B-glucose responses in two identical oral glucose tolerance tests.

Recently, the diagnostic criteria for type 2 diabetes mellitus have been changed, but there are disagreements about which measurements should be used. In contrast to the American Diabetes Association (ADA), The World Health Organization (WHO) still recognizes fasting and 2-h glucose concentrations measured on either plasma or whole blood as diagnostic tools. Insulin sensitivity and insulin secretion are both assumed to be involved in the pathogenesis of type 2 diabetes. The oral glucose tolerance test (OGTT) for estimating insulin sensitivity and secretion is increasingly used, e.g. in intervention trials. The objectives of this study were to estimate the coefficients of intra-individual variation (CVw) of blood glucose and serum insulin concentrations from an OGTT as well as indices of insulin sensitivity (HOMA) and insulin secretion (delta insulin30/delta glucose30) derived from this test. Following duplicate OGTTs with a median interval of 13 days (range 1-87 days), the analytical, inter-individual, and intra-individual coefficients of variation were calculated by nested ANOVA. The CVw for fasting blood glucose (7%) was considerably lower than that for 2-h post-load glucose (15%), which was again lower than for the insulin concentrations and indices of insulin sensitivity and secretion. In conclusion, the intra-individual variation is larger for 2-h post-load glucose than for fasting glucose and may question the continued use of the 2-h post-load glucose value in the diagnosis of type 2 diabetes.

Soluble CD163: a marker molecule for monocyte/macrophage activity in disease.

By immunoprecipitation we have identified a soluble plasma form of CD163 (sCD163), the IL-6 inducible macrophage-receptor for clearing haptoglobin-haemoglobin complexes. A sandwich ELISA for measuring sCD163 was established and used to determine the sCD163 levels in normal subjects and patients with inflammatory and myeloproliferative diseases. In normal subjects, the concentration of sCD163 was high (median 1.9 mg/l) with low intra-individual variation. Highly increased levels were seen in patients with sepsis, myeloid leukaemia and in patients with Gaucher disease characterized by accumulation of tissue macrophages. Although the physiological role of sCD163 remains unknown, our present data suggest that sCD163 might prove to be a valuable marker molecule in infectious and myeloproliferative diseases.

Optimization of preanalytical conditions and analysis of plasma glucose. 1. Impact of the new WHO and ADA recommendations on diagnosis of diabetes mellitus.

The new diagnostic criteria for type 2 diabetes from the American Diabetes Association (ADA) and World Health Organization (WHO) recommend measurements on plasma and a lowering of the glucose threshold for diabetes by 0.8 mmol/L. This narrows the distance between the upper end of the reference limit and the discriminatory level to a degree where analytical quality becomes critical. The quality demands for the preanalytical and analytical phase and their consequences on diagnostic performance have to be established in the new technical system, measuring in plasma rather than in capillary whole blood. Because of the instability of glucose in blood samples it is necessary to clarify the influence of different preanalytical and analytical factors on the number of false-positive and false-negative classifications. Thus the aim of the present study was to find optimal conditions for sampling, additives, storage, transport and analysis of plasma glucose combining feasibility with an analytical bias close to zero and a within-imprecision around 1%. We have documented the analytical performance of the method itself and its traceability to an international standard. The preanalytical conditions, such as influence of antiglycolytic agent NaF, conditions for plasma separation, storage temperature and storage time before and after plasma separation were investigated. In conclusion, we recommend that blood should be drawn in tubes containing heparin and NaF and kept on ice water for not more than 1 h until centrifugation at minimum 1000 x g for 10 min. The plasma is then stable for at least 48 h at room temperature.

Plasma glucose reference interval in a low-risk population. 2. Impact of the new WHO and ADA recommendations on the diagnosis of diabetes mellitus.

The aim of the study was to establish a reference interval of fasting venous plasma glucose (FPG) from healthy individuals. A prospective modified cross-sectional population-based study was made with random selection of 2100 persons in age-stratified groups > or = 18 years identified from the local Personal Identification Register. The invitation was accepted by 755 persons, of which 726 aged 18-92 years were eligible. They did not have a diabetes diagnosis, were non-pregnant and capable of fasting for 8 h. All participants filled in a questionnaire on medical risk factors. Blood for the FPG and haemoglobin Alc (HbAlc) measurements was drawn in accordance with a standardized procedure. A total of 302 participants carried diabetes risk indicators and were ruled out. The FPG concentrations in the remaining low-risk population (n=424) was ln Gaussian distributed. The FPG 97.50 centile in this group was 6.4 mmol/L (95% CI: 6.3-6.5 mmol/L), in contrast to the WHO and ADA theoretical limit of 6.1 mmol/L. Their diagnostic decision limit of 7.0 mmol/L FPG corresponded to the 99.86 centile of the FPG reference distribution (95% CI: 6.8-7.1). Subclassification of the reference population showed increasing FPG with increasing BMI and age and was higher in men than in women. The study determined the FPG 95% interfractile reference interval in a healthy population. The interval in glucose concentration between the 97.5 centile of the reference interval and the ADA-WHO diagnostic limit is very narrow. The clinical application of the diagnostic discriminator and the interpretation of the WHO-ADA grey zone from 6.1 to 7.0 mmol/L FPG may consequently be biased because of poorly defined limits and influence from BMI, age and gender.

Evaluation of systematic and random factors in measurements of fasting plasma glucose as the basis for analytical quality specifications in the diagnosis of diabetes. 3. Impact of the new WHO and ADA recommendations on diagnosis of diabetes mellitus.

On behalf of the Danish Society of Clinical Endocrinology and the Danish Society of Clinical Chemistry we were commissioned to evaluate the influence of analytical and pre-analytical systematic and random factors on the diagnosis of diabetes, in order to provide a tool for conclusions on the analytical quality specifications needed to diagnose diabetes. A systems analysis was performed in accordance with the principles for evaluation of analytical quality specifications. The clinical setting was defined--diagnosis of diabetes in accordance with the WHO and ADA criteria with determination of fasting plasma glucose concentration (FPG) > or =7.0 mmol/L in two independent samples--with well-documented data on In (loge)-Gaussian distribution of reference values from a low-risk population and values for within-subject biological variation taken from the literature. An investigation was made of the consequences for the clinical setting of assumed errors related to the measurement of FPG. Four approaches were investigated for a single sampling and measurement and also for two independent samples: one showing the percentage of healthy individuals who had values > or = 7.0 mmol/L, one illustrating the origin of biological set-points for results > or = 7.0 mmol/L, one showing the risk of being measured > or =7.0 mmol/L when the biological set-point is known, and one showing the combined bias and imprecision for assumed percentages of false-positive (FP), defined as measurements > or = 7.0 mmol/L for the low-risk population and false-negative (FN), defined as measurements <6.4 mmol/L (the upper reference limit) for diabetics. This leaves a "grey zone" which includes the upper part of low-risk individuals, and defined by ADA and WHO as "impaired fasting glucose" (IFG). In the analysis, increasing systematic and random errors (combined analytical and pre-analytical) were assumed, and for each error condition the fractions of FP and FN were calculated. This gave plots from which the combined allowable systematic and random errors could be read off for pre-determined clinically acceptable fractions of FP and FN. The analysis does not distinguish between pre-analytical and analytical errors, as specified information on one of these is needed for specification of the other. The investigation provides a reliable basis for estimation of the needed analytical quality, and thereby for decisions about analytical quality specifications for analysis of FPG in relation to diagnosis of diabetes under optimized pre-analytical and analytical conditions. Consequences of deviations from these ideal conditions are illustrated in the figures, and should be considered for the different approaches with different performance conditions.

Serum lactate dehydrogenase isoenzyme 1 and prediction of death in patients with metastatic testicular germ cell tumors.

The International Germ Cell Cancer Collaborative Group study of patients with metastatic testicular germ cell tumors showed that catalytic concentration of serum lactate dehydrogenase (S-LD), serum alpha-fetoprotein concentration (S-AFP), and serum human chorionic gonadotropin concentration (S-hCG) predicted death from tumor. The recent international TNM classification (T primary tumor, N lymph node metastasis, M distant metastasis) is based on these results. The aim of our study was to evaluate whether catalytic concentration of S-LD isoenzyme 1 (S-LD-1) was a better predictor than the criteria used for the international classification. In an evaluation series of 44 patients from Odense University Hospital, Denmark, a raised S-LD-1 (>1.0 x upper limit of reference values) had a predictive value for death from tumor in 5-years observation of 46%. The predictive value was 46% for S-LD, 25% for S-AFP, and 40% for S-hCG. A normal SLD-1 had a predictive value for survival over 5-years observation of 100%. It was 81% for S-LD, 75% for SAFP, and 77% for S-hCG. The fraction of the patients who died of tumor and had a raised tumor marker value was 100% for S-LD-1, 46% for S-LD, 9% for S-AFP, and 18% for S-hCG. The fraction of patients with a normal serum tumor marker value among those who survived was 61% for S-LD-1, 81% for S-LD, 94% for SAFP, and 94% for S-hCG. A validation series of 37 patients treated at the University of Texas MD Anderson Cancer Center showed similar findings. Combining the patients in the two series, a raised value of SLD-1 classified more patients into a subgroup with an impaired survival (53%) than S-LD (35%), S-AFP (6%), or S-hCG (11%), and the high risk subgroups based on the international classification (40%). The findings have implications for the staging and treatment of patients with metastatic testicular germ cell tumors.

Evidence for a substantial genetic influence on biochemical liver function tests: results from a population-based Danish twin study.

BACKGROUND: Biochemical liver function tests are widely used in the clinic and are some of the most frequently used tests in screening for diseases in older age groups. The aim of the present study was to estimate the relative importance of genetic and environmental factors to variations in these tests among the elderly. METHODS: We conducted a survey among Danish twins, 73-102 years of age, identified in the population-based Danish Twin Registry. Among the 2749 individuals in the study population, an interview was conducted with 79%. From these, a blood sample was collected from 290 same-sex twin pairs, total of 580 subjects, within a 6-month period and analyzed for alanine aminotransferase (ALT), lactate dehydrogenase (LDH), gamma-glutamyltransferase (GGT), bilirubin, and albumin. The interview included questions about alcohol consumption and body mass index (BMI; self-calculated height and weight). Heritability (proportion of the population variance attributable to genetic variation) was estimated using structural-equation analyses before and after correction for alcohol consumption and BMI. RESULTS: Structural-equation analyses revealed a substantial heritability (35-61%) for the four biochemical liver function tests: ALT, GGT, LDH, and bilirubin. The remaining variation could be attributed to individuals' nonfamilial environments. Adjustment for alcohol consumption and BMI had no influence on the heritability for ALT, GGT, LDH, and bilirubin. For albumin, two models fit equally well before adjustment for alcohol and BMI: a model including additive genetic and nonshared environmental factors (AE), and a model including shared and nonshared environmental factors (CE). After adjustment, the model including shared and nonshared environment was clearly the best fitting model. CONCLUSIONS: For both males and females, the effect of genetic factors on the biochemical liver function tests ALT, GGT, LDH, and bilirubin is substantial and accounts for one-third to two-thirds of the variation among individuals 73-102 years of age. The heritability is equal for males and females and does not change notably after controlling for alcohol consumption and BMI. For albumin, no major impact of genetic factors was found independent of BMI and alcohol consumption. An understanding of the genetic mechanisms underlying biochemical liver function tests among the very old may be of value in the interpretation of these tests in this age group.

Progression criteria for cancer antigen 15.3 and carcinoembryonic antigen in metastatic breast cancer compared by computer simulation of marker data.

BACKGROUND: We investigated the utility of computer simulation models for performance comparisons of different tumor marker assessment criteria to define progression or nonprogression of metastatic breast cancer. METHODS: Clinically relevant values for progressive cancer antigen 15.3 and carcinoembryonic antigen concentrations were combined with representative values for background variations in a computer simulation model. Fifteen criteria for assessment of longitudinal tumor marker data were obtained from the literature and computerized. Altogether, 7200 different patients, each based on 50 measurements, were simulated. With a sampling interval of 4 weeks, the monitoring period for each event was approximately 3.8 years. RESULTS: Modulation of the background variation, the starting concentrations, and the cutoffs enabled identification of criteria that were robust against false-positive signals of progression. CONCLUSIONS: The computer simulation model is a fast, effective, and inexpensive approach for comparing the diagnostic potential of assessment criteria during clinically relevant conditions of steady-state and progressive disease. The model systems can be used to generate tumor marker assessment criteria for a variety of malignancies and to compare and optimize their diagnostic performance.

Validity of susceptibility testing of uropathogenic bacteria in general practice.

Resistance of uropathogenic bacteria to antibiotics is an increasing problem in primary health care. The aim of this study was to evaluate antibacterial susceptibility testing of uropathogenic bacteria when performed in general practice. Urine specimens with a known quantity of typically uropathogenic bacteria were sent to 25 general practices. The predictive values of testing a bacterial strain as susceptible ranged from 0.89 (nitrofurantoin) to 1.00 (sulphamethizole), and the predictive value of testing a bacterial strain as resistant ranged from 0.55 (trimethoprim) to 0.90 (nitrofurantoin). Interventions to improve the validity of susceptibility testing are desirable if the test should be incorporated in the diagnostic armamentarium in general practice.