Definitions and major prerequisites of direct and indirect approaches for estimating reference limits

Reference intervals are established either by direct or indirect approaches. Whereas the definition of direct is well established, the definition of indirect is still a matter of debate. In this paper, a general definition that covers all indirect models presently in use is proposed. With the upcoming popularity of indirect models, it has become evident that further partitioning strategies are required to minimize the risk of patients' false classifications. With indirect methods, such partitions are much easier to execute than with direct methods. The authors believe that the future of reference interval estimation belongs to indirect models with big data pools either from one laboratory or combined from several regional centres (if necessary). Independent of the approach applied, the quality assurance of the pre-analytical and analytical phase, considering biological variables and other confounding factors, is essential.

Age-and sex-specific reference intervals of total cholesterol, LDL cholesterol, HDL cholesterol and non-HDL cholesterol. Comparison of two algorithms for the indirect estimation of reference intervals

Objectives

Reference intervals of total cholesterol concentrations in plasma and of their fractions low-density lipoprotein (LDL)-, high-density lipoprotein (HDL)-and non-HDL concentrations are seldom studied with respect to the relevance of age and sex. Therefore, the effect of age and sex on the reference intervals was reinvestigated with 2 indirect procedures.

Methods

As an indirect approach, the truncated minimum chi-square method was applied. All analyses were performed by computer programs available. The script published on the homepage of the German Society of Clinical Chemistry and Laboratory Medicine (DGKL) allows to derive a continuous age dependency of reference intervals together with their confidence and equivalence limits. The results of this approach were compared with those obtained by an indirect method developed more recently, the refineR algorithm.

Results

In the present study, the upper reference limits of total cholesterol varied from 5.1 to 7.8 mmol/L (197–302 mg/dL) depending on various biological variables (as age, sex, inpatients versus outpatients). These upper limits increased with age. Differences between sexes can be neglected except for the age above 80 years. The pattern of reference limits of LDL cholesterol and non-HDL cholesterol paralleled those of total cholesterol. The reference limits of HDL cholesterol were higher in women than in men but were independent of age.

Conclusions

Reference limits for the concentrations of total cholesterol and their fractions LDL-, HDL-and non-HDL concentrations should be stratified for age and sex.

Problems with estimating reference change values (critical differences)

The concept of reference change values (RCVs) for diagnosis and monitoring of diseases has become well established. Several models habe been developed, e. g. one assuming a normal distribution and another one for a log-normal distribution. RCV values calculated for some measurands with both models are compared with each other and led to similar results. A few examples led to RCV values which are not plausible for diagnostic purposes. Although statistical concepts of RCV values are well established, their clinical relevance remains questionable at least for some measurands. Studies with clinicians are required whether RCVs are of practical usefulness.

The importance of correct stratifications when comparing directly and indirectly estimated reference intervals

OBJECTIVES

There are generally two major reasons for the comparison of reference intervals (RIs): when externally determined RIs (from the literature or provided by a manufacturer) are compared with presently used intra-laboratory RIs and when indirectly estimated RIs are compared with directly established RIs. Discrepancies within these comparisons may occur for two reasons: 1. the pre-analytical and/or analytical conditions do not agree and/or 2. biological variables influencing the establishment of RIs have not been considered adequately. If directly and indirectly estimated reference intervals (RIs) are compared with each other, they very often agree. Sometimes, however, a comparison may differ, with the reason for any discrepancy not being further studied. A major reason for differences in the comparison of RIs is that the requirement for stratification has been neglected.

METHODS

The present report outlines the consequences to RI comparison if stratification is neglected during RI determination with the main variables affecting RIs being sex and age. Alanine aminotransferase was chosen as an example in which the RIs depend on both these factors.

RESULTS

Both direct and indirect approaches lead to erroneous RIs if stratification for variables which are known to affect the estimation of RIs is not performed adequately. However, failing to include a required stratification in procedures for directly determined RIs affects the outcome in a different way to indirectly determined RIs.

CONCLUSIONS

The resulting difference between direct and indirect RIs is often misinterpreted as an incorrect RI estimation of the indirect method.

Review of potentials and limitations of indirect approaches for estimating reference limits/intervals of quantitative procedures in laboratory medicine

Reference intervals (RIs) can be determined by direct and indirect procedures. Both approaches identify a reference population from which the RIs are defined. The crucial difference between direct and indirect methods is that direct methods select particular individuals after individual anamnesis and medical examination have confirmed the absence of pathological conditions. These individuals form a reference subpopulation. Indirect methods select a reference subpopulation in which the individuals are not identified. They isolate a reference population from a mixed population of patients with pathological and non-pathological conditions by statistical reasoning.

At present, the direct procedure internationally recommended is the “gold standard”. It has, however, the disadvantage of high expenses which cannot easily be afforded by most medical laboratories. Therefore, laboratories adopt RIs established by direct methods from external sources requiring a high responsibility for transference problems which are usually neglected by most laboratories. These difficulties can be overcome by indirect procedures which can easily be performed by most laboratories without causing economic problems.

The present review focuses on indirect approaches. Various procedures are presented with their benefits and limitations. Preliminary simulation studies indicate that more recently developed concepts are superior to older approaches.

Age and sex dependent reference intervals for random plasma/serum glucose concentrations related to different sampling devices and determined by an indirect procedure with data mining

The glucose concentration in plasma or serum is one of the most often requested analytical values in laboratory medicine. Whereas the analytical part of the glucose determination is well standardised, the standardisation of the pre-examination part (pre-analytical phase) is not sufficiently solved, yet. In view of the present controversial discussion regarding the most efficient prevention of pre-analytical glycolysis, the question arises whether the economical and logistic expenses for inhibiting glycolysis determining random glucose concentration are justified. In hospitals with adequate logistics (e.g. pneumatic tube systems for blood tubes) to guarantee a blood sample transport time of about 1 – 2 h, plasma or serum without prevention of glycolysis can be applied for random glucose concentrations if the reference limits are estimated by the laboratory. If such logistics are not available, especially in primary care services, either plasma or serum samples or whole blood in special tubes with anti-glycolytic additives may be sent to the laboratory.

Age- and sex-dependent reference intervals for uric acid estimated by the truncated minimum chi-square (TMC) approach, a new indirect method

Background

Although the concentration of uric acid in serum or plasma is known to depend on sex and age and is subject to diurnal variation, the influence of these covariates on the reference interval (RI) is often neglected. Consequently, the values in the literature vary considerably. Therefore, we reinvestigated the reference limits and their dependence on covariates.

Methods

A new indirect approach was applied which derives a continuous function between age and RIs avoiding the usual “jumps” between various age groups.

Results

It is confirmed that the uric acid concentration in women is lower than in men. The RIs increase with age, in women more than in men. Between 80 and 90 years of age, the upper RI limit (RL) approximately reaches the same level in both sexes. Because the uric acid concentration may indicate renal insufficiency, the concentrations of creatinine and cystatin C were also measured. Both measurands showed the same behaviour as uric acid. Therefore, the age and sex dependency should be considered if the uric acid concentration is used as an indicator for hyperuricaemia (e.g. caused by gout or other metabolic diseases). Furthermore, a diurnal variation was observed.

Conclusions

Due to the variations of various covariates (age, sex, daytime, analytical systems), it is recommended that each laboratory should estimate its own RIs.

A new indirect estimation of reference intervals: truncated minimum chi-square (TMC) approach

All known direct and indirect approaches for the estimation of reference intervals (RIs) have difficulties in processing very skewed data with a high percentage of values at or below the detection limit. A new model for the indirect estimation of RIs is proposed, which can be applied even to extremely skewed data distributions with a relatively high percentage of data at or below the detection limit. Furthermore, it fits better to some simulated data files than other indirect methods. The approach starts with a quantile-quantile plot providing preliminary estimates for the parameters (λ, μ, σ) of the assumed power normal distribution. These are iteratively refined by a truncated minimum chi-square (TMC) estimation. The finally estimated parameters are used to calculate the 95% reference interval. Confidence intervals for the interval limits are calculated by the asymptotic formula for quantiles, and tolerance limits are determined via bootstrapping. If age intervals are given, the procedure is applied per age interval and a spline function describes the age dependency of the reference limits by a continuous function. The approach can be performed in the statistical package R and on the Excel platform.

Serum Levels of MicroRNA-371a-3p (M371 Test) as a New Biomarker of Testicular Germ Cell Tumors: Results of a Prospective Multicentric Study

PURPOSE

Previous studies suggested that serum levels of microRNA (miR)-371a-3p (so-called M371 test) have a much higher sensitivity and specificity than the classic markers of testicular germ cell tumors (GCTs) and are applicable toward both seminoma and nonseminoma. We sought to confirm the usefulness of this test as a novel biomarker for GCT.

PATIENTS AND METHODS

In a prospective, multicentric study, serum samples of 616 patients with testicular GCTs and 258 male controls were examined for serum levels of miRNA-371a-3p (miR levels) by quantitative polymerase chain reaction. The GCT population encompassed 359 patients with seminoma and 257 with nonseminoma; 371 had clinical stage I disease, 201 had systemic disease, and 46 had relapses. Paired measurements before and after orchiectomy were performed in 424 patients; 118 with systemic disease had serial measurements during treatment. miR levels were compared with those of β-human chorionic gonadotropin, α-fetoprotein, and lactate dehydrogenase.

RESULTS

For the primary diagnosis of GCT, the M371 test showed a sensitivity of 90.1%, a specificity of 94.0%, an area under the curve of 0.966 upon receiver operating characteristic analysis, and a positive predictive value of 97.2%. α-Fetoprotein, β-human chorionic gonadotropin, and lactate dehydrogenase had sensitivities of less than 50% in seminoma and slightly higher sensitivities in nonseminomas. miR levels were significantly associated with clinical stage, primary tumor size, and response to treatment. Relapses had elevated miR levels that subsequently dropped to normal upon remission. Teratoma did not express miR-371a-3p.

CONCLUSION

The M371 test outperforms the classic markers of GCT with both a sensitivity and a specificity greater than 90%. All histologic subgroups, except teratoma, express this marker. The test could be considered for clinical implementation after further validation.

Erratum to: Reply to the EFSA (2016) on the relevance of recent publications (Hofmann et al. 2014, 2016) on environmental risk assessment and management of Bt-maize events (MON810, Bt11 and 1507)

[This corrects the article DOI: 10.1186/s12302-017-0106-0.].

Quantity quotient reporting versus z-value for standardizing quantitative laboratory results

The rapid increase to digitalize whatever is possible in human lives will lead to electronic storage of medical data probably during the whole life of most individuals. This requires standardization and condensation of an enormous amount of data. Most laboratory data are already reported in digitalized form, but they are far from being sufficiently standardized. Several attempts for standardization have been suggested. The most common standardizing approach is the z-transformation of laboratory data. It is proposed to modify the z-value to a quantity quotient in analogy to the intelligence quotient well known even to laymen.

Reply to the EFSA (2016) on the relevance of recent publications (Hofmann et al. 2014, 2016) on environmental risk assessment and management of Bt-maize events (MON810, Bt11 and 1507)

In this commentary, we respond to a report of the EFSA GMO Panel (EFSA EFSA Supp Publ, 1) that criticises the outcomes of two studies published in this journal (Hofmann et al. Environ Sci Eur 26: 24, 2; Environ Sci Eur 28: 14, 3). Both publications relate to the environmental risk assessment and management of Bt-maize, including maize events MON810, Bt11 and maize 1507. The results of Hofmann et al. (Environ Sci Eur 26: 24, 2), using standardised pollen mass filter deposition measurements, indicated that the EFSA Panel model had underestimated pollen deposition and, hence, exposure of non-target organisms to Bt-maize pollen. The results implied a need for safety buffer distances in the kilometre range for protected nature reserve areas instead of the 20-30 m range recommended by the EFSA Panel. As a result, the EFSA Panel revised their model (EFSA EFSA J 13: 4127, 4), adopting the slope of the empirical data from Hofmann et al. The intercept, however, was substantially reduced to less than 1% at one point by introducing further assumptions based on the estimates of mainly panel members, citing possible 'uncertainty'. Hofmann et al. (Environ Sci Eur 28: 14, 3) published extensive empirical data regarding pollen deposition on leaves. These results were part of a larger 3-year study involving detailed measurements of pollen release, dispersal and deposition over the maize flowering period. The data collected in situ confirmed the previous predictions of Hofmann et al. (Environ Sci Eur 26: 24, 2). Mean levels and observed variability of pollen deposition on maize and four lepidopteran host plants exceeded the assumptions and disagreed with the conclusions of the EFSA Panel. The EFSA Panel reacted in a report (EFSA EFSA Supp Publ, 1) criticising the methods and outcomes of the two published studies of Hofmann et al. while reaffirming their original recommendations. We respond here point-by-point, showing that the critique is not justified. Based on our results on Urtica leaf pollen density, we confirm the need for specific environmental impact assessments for Bt-maize cultivation with respect to protected habitats within isolation buffer distances in the kilometre range.

Mercury species in dab (Limanda limanda) from the North Sea, Baltic Sea and Icelandic waters in relation to host-specific variables

In the framework of the ICON project (Integrated Assessment of Contaminant Impacts on the North Sea), muscle tissue from a total of 135 common dab (Limanda limanda) (20-28 cm total length) was collected in seven offshore sampling areas in the North Sea, at Iceland and in the Baltic Sea during Aug/Sept and December 2008 for a chemical mercury speciation analysis by means of gas chromatography and detection by cold vapour atomic fluorescence spectroscopy (GC-CVAFS). There was a highly significant correlation between concentrations of methylmercury (MeHg⁺) and inorganic mercury (Hg²⁺) in individual fish, and the mean ratio of MeHg⁺ compared to Σ Hg (MeHg⁺ + Hg²⁺) was 94.0%. The results revealed statistically significant differences in concentrations of MeHg⁺ and Hg²⁺, respectively, between sampling areas. Mean concentrations in the German Bight (North Sea), in Icelandic waters and in Mecklenburg Bight (Baltic Sea) were low (MeHg⁺: 0.023-0.036; Hg²⁺: 0.001-0.002 mg/kg wet weight), while concentrations in dab from the Dogger Bank, Firth of Forth and the vicinity of the Ekofisk oil field (all North Sea) were significantly higher (MeHg⁺: 0.059-0.101; Hg²⁺: 0.003-0.004 mg/kg wet weight). Statistical correlation analysis on effects of host-specific factors revealed that neither length, weight, age, sex nor condition factor showed a significant relationship with Hg concentrations. However, Hg concentrations were significantly correlated with the Fish Disease Index (FDI), indicating a relationship between Hg concentrations and the health status of dab. Multiple linear regression analysis aiming to find factors affecting Hg concentrations revealed that only the sampling area had a highly significant main effect on Hg concentrations, and in some cases, additionally the condition factor contributed significantly to the final model. From the results, it cannot be excluded that elevated Hg concentration recorded in dab were linked to discharges from offshore oil and gas installations and that Hg affected the health status of dab.

Diseases of dab (Limanda limanda): Analysis and assessment of data on externally visible diseases, macroscopic liver neoplasms and liver histopathology in the North Sea, Baltic Sea and off Iceland

In the framework of the ICON project (Integrated Assessment of Contaminant Impacts on the North Sea), common dab (Limanda limanda) from seven offshore sampling areas in the North Sea, Icelandic waters and the western Baltic Sea were examined in 2008 for the presence of externally visible diseases and parasites (EVD), macroscopic liver neoplasms (tumours) (MLN) and histopathological liver lesions (LH). Methodologies applied followed standardised ICES and BEQUALM protocols. The EDV results revealed pronounced spatial variation, with dab from the central and northern North Sea sampling areas showing the highest disease prevalence. MLN were recorded only in North Sea dab from the German Bight, Firth of Forth and Ekofisk at a low prevalence. LH results revealed a dominant prevalence of non-specific, mostly inflammatory, lesions and a low prevalence of early toxicopathic non-neoplastic lesions, tumour pre-stages (foci of cellular alteration) and liver tumours. For the analysis and assessment of spatial variation of EVD, a Fish Disease Index (FDI) was calculated for individual dab, summarising data on the presence/absence of EDV, their severity grades, effects on the host and compensating for effects of length, sex and season. FDI data confirmed that the health status of North Sea dab from the offshore areas Dogger Bank, Ekofisk and Firth of Forth was significantly worse than in dab from the German Bight, Icelandic areas and the western Baltic Sea. An assessment of the disease data following ICES/OSPAR criteria was accomplished by applying established numeric background (BAC) and ecological assessment criteria (EAC) for EDV, MLN and LH. The combined assessment of the three disease categories indicated that health effects classified as unacceptable were rare and mainly affected dab from the North Sea. Based on the findings of the present study, it is recommended to monitor wild fish diseases in the context of assessing the impact of hazardous substances and other stressors on the marine environment. The Fish Disease Index (FDI) is regarded as a strong tool for disease data analysis and assessment, suitable as ecosystem health indicator.

Integrated indicator framework and methodology for monitoring and assessment of hazardous substances and their effects in the marine environment

Many maritime countries in Europe have implemented marine environmental monitoring programmes which include the measurement of chemical contaminants and related biological effects. How best to integrate data obtained in these two types of monitoring into meaningful assessments has been the subject of recent efforts by the International Council for Exploration of the Sea (ICES) Expert Groups. Work within these groups has concentrated on defining a core set of chemical and biological endpoints that can be used across maritime areas, defining confounding factors, supporting parameters and protocols for measurement. The framework comprised markers for concentrations of, exposure to and effects from, contaminants. Most importantly, assessment criteria for biological effect measurements have been set and the framework suggests how these measurements can be used in an integrated manner alongside contaminant measurements in biota, sediments and potentially water. Output from this process resulted in OSPAR Commission (www.ospar.org) guidelines that were adopted in 2012 on a trial basis for a period of 3 years. The developed assessment framework can furthermore provide a suitable approach for the assessment of Good Environmental Status (GES) for Descriptor 8 of the European Union (EU) Marine Strategy Framework Directive (MSFD).

Resources of dark skies in German climatic health resorts

Illumination of nocturnal environments is increasing steadily worldwide. While there are some benefits for mankind, light at night affects animals, plants, and human health by blurring the natural distinction between day and night. International regulations exist to protect the environment for the maintenance of human health but nocturnal darkness is not considered. In Germany, cities and communities labeled as Climatic Health Resorts provide for high standards in air quality. However, their degree of nocturnal darkness is unexplored so far. In our study, we examined the degree of nocturnal darkness in German Climatic Health Resorts by two datasets based on georeferenced remote sensing data. The majority of Climatic Health Resorts (93.1 %) are able to offer a relative respite (≥ 20 mag/arcsec²) from a degraded nocturnal environment, while only 3.4 % are able to offer a dark, if by no means pristine, night environment (≥ 21 mag/arcsec²). Climatic Health Resorts emit less light as well as are less affected by night sky brightness compared to the average of non-classified communities. In combination with daytime requirements, the resorts provide conditions for a more distinct day-and-night-cycle than non-classified communities.

Critical comments to a recent EFLM recommendation for the review of reference intervals

In a recent EFLM recommendation on reference intervals by Henny et al., the direct approach for determining reference intervals was proposed as the only presently accepted “gold” standard. Some essential drawbacks of the direct approach were not sufficiently emphasized, such as unacceptably wide confidence limits due to the limited number of observations claimed and the practical usability for only a limited age range. Indirect procedures avoid these disadvantages of the direct approach. Furthermore, indirect approaches are well suited for reference limits with large variations during lifetime and for common reference limits.

Challenges and Perspectives in Bridging In- and Outpatient Sectors: The Implementation of Two Alternative Models of Care and Their Effect on the Average Length of Stay

New models of care aimed at reinforcing the outpatient sector have been introduced in Germany over the last few years. Initially, a subscription-based model ("integrated care") was introduced in 2012 in the Immanuel Klinik Rüdersdorf, wherein patients had to actively subscribe to the integrated care program. This integrated care model was replaced after 2 years by a subscription-free "model project," in which all patients insured by the contracting insurance company took part in the program. Data showed that the introduction of the integrated care program in the inpatient setting led to an increase of the average length of stay in this group. The switch to the model project corrected this unwanted effect but failed in significantly decreasing the average length of stay when compared to standard care. However, both the integrated care program and model project succeeded in reducing the length of stay in the day care setting. When adjusting for the sex and diagnosis proportions of each year, it was shown that diagnosis strongly influenced the average length of stay in both settings, whereas sex only slightly influenced the duration of stay in the inpatient setting. Thus, in spite of strong financial and clinical incentives, the introduction of the model project couldn't fulfill its primary purpose of shifting resources from the inpatient to the outpatient setting in the initial years. Possible explanations, including struggle against long-established traditions and reluctance to change, are discussed.

Myocardial scintigraphy - a method for detecting cardiac comorbidity in psoriasis patients?

BACKGROUND

In recent years, cardiac comorbidities in psoriasis patients have increasingly moved into the focus of clinical research. The objective of the present study was to evaluate myocardial scintigraphy as a screening method in patients with psoriasis.

PATIENTS AND METHODS

Assessment of various comorbidities in 50 psoriasis patients without clinical symptoms of cardiac disease. Myocardial scintigraphy was employed to detect cardiac risk/exercise-induced ischemia.

RESULTS

Twenty-eight patients (56 %) had pathological findings on myocardial scintigraphy. Fourteen individuals showed evidence of small-vessel disease (cardiac syndrome X). Other comorbidities included obesity, arterial hypertension, nicotine and alcohol abuse, as well as elevated CRP levels. Frequencies largely corresponded to those reported in the recent literature. There was no significant correlation between the severity of psoriasis or any comorbidities and pathological findings on myocardial scintigraphy.

CONCLUSIONS

Myocardial scintigraphy seems to be a very sensitive, noninvasive method for the early detection of cardiac comorbidities in psoriasis patients. However, determining its true diagnostic value will require larger studies with control subjects and control methods such as coronary angiography.

Serum Levels of MicroRNA miR-371a-3p: A Sensitive and Specific New Biomarker for Germ Cell Tumours

BACKGROUND

Clinical management of germ cell tumours (GCTs) relies on monitoring of serum tumour markers. However, the markers α-fetoprotein (AFP), the β-subunit of human chorionic gonadotropin (bHCG), and lactate dehydrogenase (LDH) are expressed in <60% of GCT cases.

OBJECTIVE

To test the utility of the microRNAs (miRNAs) miR-371a-3p, miR-372-3p, miR-373-3p, and miR-367-3p as sensitive and specific GCT serum biomarkers.

DESIGN, SETTING, AND PARTICIPANTS

Serum levels of miRNAs were measured in 166 consecutive patients with GCT before and after treatment and in 106 male controls. In the first 50 consecutive patients, all four miRNAs were measured. In the main study, only the most sensitive miRNA was further analysed.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The specificity and sensitivity of the four miRNAs were studied using receiver operating characteristic curves. miRNA sensitivities were compared to those of classical markers. Statistical cross-comparisons of miRNA levels for GCT subgroups and controls were performed at various time points during treatment.

RESULTS AND LIMITATIONS

Overall, miR-371a-3p performed best, with 88.7% sensitivity (95% confidence interval [CI] 82.5-93.3%) and 93.4% specificity (95% CI 86.9-97.3%) and an area under the curve of 0.94, outperforming AFP, bHCG, and LDH (combined sensitivity 50%). According to Kernel density estimation, the sensitivity and specificity were 86.3% and 92.5%, respectively. miR-371a-3p levels dropped to normal after completion of treatment. The miRNA levels correlated with treatment failure and relapse. Teratoma did not express miR-371a-3p.

CONCLUSIONS

The miRNA miR-371a-3p is a specific and sensitive novel serum GCT biomarker that accurately correlates with disease activity. Validation of this test in a large-scale prospective study is needed. PATIENT SUMMARY: miR-371a-3p is a novel serum marker for germ cell tumours that is expressed by 88.7% of patients and thus is far more sensitive and specific than classical serum markers. It correlates with tumour burden and treatment results. Validation in a large patient cohort is needed.

Spatially valid data of atmospheric deposition of heavy metals and nitrogen derived by moss surveys for pollution risk assessments of ecosystems

For analysing element input into ecosystems and associated risks due to atmospheric deposition, element concentrations in moss provide complementary and time-integrated data at high spatial resolution every 5 years since 1990. The paper reviews (1) minimum sample sizes needed for reliable, statistical estimation of mean values at four different spatial scales (European and national level as well as landscape-specific level covering Europe and single countries); (2) trends of heavy metal (HM) and nitrogen (N) concentrations in moss in Europe (1990-2010); (3) correlations between concentrations of HM in moss and soil specimens collected across Norway (1990-2010); and (4) canopy drip-induced site-specific variation of N concentration in moss sampled in seven European countries (1990-2013). While the minimum sample sizes on the European and national level were achieved without exception, for some ecological land classes and elements, the coverage with sampling sites should be improved. The decline in emission and subsequent atmospheric deposition of HM across Europe has resulted in decreasing HM concentrations in moss between 1990 and 2010. In contrast, hardly any changes were observed for N in moss between 2005, when N was included into the survey for the first time, and 2010. In Norway, both, the moss and the soil survey data sets, were correlated, indicating a decrease of HM concentrations in moss and soil. At the site level, the average N deposition inside of forests was almost three times higher than the average N deposition outside of forests.

Accumulation and variability of maize pollen deposition on leaves of European Lepidoptera host plants and relation to release rates and deposition determined by standardised technical sampling

BACKGROUND

Risk assessment for GMOs such as Bt maize requires detailed data concerning pollen deposition onto non-target host-plant leaves. A field study of pollen on lepidopteran host-plant leaves was therefore undertaken in 2009-2012 in Germany. During the maize flowering period, we used in situ microscopy at a spatial resolution adequate to monitor the feeding behaviour of butterfly larvae. The plant-specific pollen deposition data were supplemented with standardised measurements of pollen release rates and deposition obtained by volumetric pollen monitors and passive samplers.

RESULTS

In 2010, we made 5377 measurements of maize pollen deposited onto leaves of maize, nettle, goosefoot, sorrel and blackberry. Overall mean leaf deposition during the flowering period ranged from 54 to 478 n/cm² (grains/cm²) depending on plant species and site, while daily mean leaf deposition values were as high as 2710 n/cm². Maximum single leaf-deposition values reached up to 103,000 n/cm², with a 95 % confidence-limit upper boundary of 11,716 n/cm².

CONCLUSIONS

Daily means and variation of single values uncovered by our detailed measurements are considerably higher than previously assumed. The recorded levels are more than a single degree of magnitude larger than actual EU expert risk assessment assumptions. Because variation and total aggregation of deposited pollen on leaves have been previously underestimated, lepidopteran larvae have actually been subjected to higher and more variable exposure. Higher risks to these organisms must consequently be assumed. Our results imply that risk assessments related to the effects of Bt maize exposure under both realistic cultivation conditions and worst-case scenarios must be revised. Under common cultivation conditions, isolation buffer distances in the kilometre range are recommended rather than the 20-30 m distance defined by the EFSA.

Permissible limits for uncertainty of measurement in laboratory medicine

The international standard ISO 15189 requires that medical laboratories estimate the uncertainty of their quantitative test results obtained from patients' specimens. The standard does not provide details how and within which limits the measurement uncertainty should be determined. The most common concept for establishing permissible uncertainty limits is to relate them on biological variation defining the rate of false positive results or to base the limits on the state-of-the-art. The state-of-the-art is usually derived from data provided by a group of selected medical laboratories. The approach on biological variation should be preferred because of its transparency and scientific base. Hitherto, all recommendations were based on a linear relationship between biological and analytical variation leading to limits which are sometimes too stringent or too permissive for routine testing in laboratory medicine. In contrast, the present proposal is based on a non-linear relationship between biological and analytical variation leading to more realistic limits. The proposed algorithms can be applied to all measurands and consider any quantity to be assured. The suggested approach tries to provide the above mentioned details and is a compromise between the biological variation concept, the GUM uncertainty model and the technical state-of-the-art.

Equivalence limits of reference intervals for partitioning of population data. Relevant differences of reference limits

Reference limits need to be compared with each other for two main purposes: to evaluate the clinical relevance of a possible difference, if limits are obtained from the same population but at different time periods, or to check if limits derived from two different subpopulations can be considered as identical. The comparison of reference limits required for the periodic reviewing of applied reference limits and for checking the transferability of reference limits adopted from external sources according to international standards is an example for the first case. In the second case, a decision is intended whether the full population has to be partitioned (stratified) into the subpopulations under consideration (e.g. males and females). In both situations, differences may be due either to analytical errors, to biological differences or to both effects. The difference between reference limits may be acceptable if it is within permissible limits. For establishing permissible limits, the concept of equivalence limits was adopted to assess the relevance of differences between two reference limits. The concept bases on the permissible uncertainty at a particular reference limit. The permissible uncertainty is quantified by the permissible analytical standard deviation derived from the empirical biological variation as recently proposed. It is defined separately for lower and upper reference limits. The concept proposed can be condensed to simple equations.

[Subscription Rates of Psychiatric Patients to an Integrated Care Program in the Context of a Psychiatric Model Project]

Objective: In the past years different model projects have been developed in Germany to counteract the known deficits of the German psychiatric care system. Among these, an "integrated care" model project has been set up which offers a more flexible way of managing psychiatric care, especially for patients with a severe mental illness. It however implies an active subscription to the program. In this study we analyzed factors influencing patients' subscription rates. Methods: Subscription rates during the first 18 months of the program were analyzed with regard to the patients' main diagnoses and gender. Results: We found an overall subscription rate of 59.3 %. Diagnosis explained 24.1 % of the overall variance of the inpatients' subscription rate. This effect was significantly smaller in outpatients. No effect of gender could be observed. The highest subscription rate was found by patients with an affective disorder. Only 34.6 % of the patients with an F2 diagnosis subscribed. Conclusion: The target groups of the program could not be sufficiently reached in this model. The need of a new legal basis for psychiatric care models, namely a subscription-free program, is thereby reinforced.

HMGA2 expression distinguishes between different types of postpubertal testicular germ cell tumour

The group of postpubertal testicular germ cell tumours encompasses lesions with highly diverse differentiation – seminomas, embryonal carcinomas, yolk sac tumours, teratomas and choriocarcinomas. Heterogeneous differentiation is often present within individual tumours and the correct identification of the components is of clinical relevance. HMGA2 re‐expression has been reported in many tumours, including testicular germ cell tumours. This is the first study investigating HMGA2 expression in a representative group of testicular germ cell tumours with the highly sensitive method of quantitative real‐time PCR as well as with immunohistochemistry. The expression of HMGA2 and HPRT was measured using quantitative real‐time PCR in 59 postpubertal testicular germ cell tumours. Thirty specimens contained only one type of tumour and 29 were mixed neoplasms. With the exception of choriocarcinomas, at least two pure specimens from each subgroup of testicular germ cell tumour were included. In order to validate the quantitative real‐time PCR data and gather information about the localisation of the protein, additional immunohistochemical analysis with an antibody specific for HMGA2 was performed in 23 cases. Expression of HMGA2 in testicular germ cell tumours depended on the histological differentiation. Seminomas and embryonal carcinomas showed no or very little expression, whereas yolk sac tumours strongly expressed HMGA2 at the transcriptome as well as the protein level. In teratomas, the expression varied and in choriocarcinomas the expression was moderate. In part, these results contradict data from previous studies but HMGA2 seems to represent a novel marker to assist pathological subtyping of testicular germ cell tumours. The results indicate a critical role in yolk sac tumours and some forms of teratoma.

Quantity quotient reporting. Comparison of various models

Quantity quotient (QQ) reporting has been proposed by several authors to improve or support the present situation of presenting quantitative laboratory results. This proposal is based on a concept (symmetrical model) known from the intelligence quotient, which was developed to make intelligence tests comparable. In laboratory medicine, however, most measurands follow a non-symmetrical (skewed) distribution, leading to a compression of the QQ values at the lower end of the reference interval. This effect can be avoided by several alternatives. Three models considering non-symmetrical distributions are compared with the symmetrical model in the present study. The corresponding algorithms can be easily handled on the Excel platform. Graphical presentation of the QQ allows a quick overview of test results if they occur in a large number.

Optimizing the use of the “state-of-the-art” performance criteria

The organizers of the first EFLM Strategic Conference “Defining analytical performance goals” identified three models for defining analytical performance goals in laboratory medicine. Whereas the highest level of model 1 (outcome studies) is difficult to implement, the other levels are more or less based on subjective opinions of experts, with models 2 (based on biological variation) and 3 (defined by the state-of-the-art) being more objective. A working group of the German Society of Clinical Chemistry and Laboratory Medicine (DGKL) proposes a combination of models 2 and 3 to overcome some disadvantages inherent to both models. In the new model, the permissible imprecision is not defined as a constant proportion of biological variation but by a non-linear relationship between permissible analytical and biological variation. Furthermore, the permissible imprecision is referred to the target quantity value. The biological variation is derived from the reference interval, if appropriate, after logarithmic transformation of the reference limits.

Correlated expression of HMGA2 and PLAG1 in thyroid tumors, uterine leiomyomas and experimental models

In pleomorphic adenomas of the salivary glands (PASG) recurrent chromosomal rearrangements affecting either 8q12 or 12q14∼15 lead to an overexpression of the genes of the genuine transcription factor PLAG1 or the architectural transcription factor HMGA2, respectively. Both genes are also affected by recurrent chromosomal rearrangements in benign adipocytic tumors as e. g. lipomas and lipoblastomas. Herein, we observed a strong correlation between the expression of HMGA2 and PLAG1 in 14 benign and 23 malignant thyroid tumors. To address the question if PLAG1 can be activated by HMGA2, the expression of both genes was quantified in 32 uterine leiomyomas 17 of which exhibited an overexpression of HMGA2. All leiomyomas with HMGA2 overexpression also revealed an activation of PLAG1 in the absence of detectable chromosome 8 abnormalities affecting the PLAG1 locus. To further investigate if the overexpression of PLAG1 is inducible by HMGA2 alone, HMGA2 was transiently overexpressed in MCF-7 cells. An increased PLAG1 expression was observed 24 and 48 h after transfection. Likewise, stimulation of HMGA2 by FGF1 in adipose tissue-derived stem cells led to a simultaneous increase of PLAG1 mRNA. Altogether, these data suggest that HMGA2 is an upstream activator of PLAG1. Accordingly, this may explain the formation of tumors as similar as lipomas and lipoblastomas resulting from an activation of either of both genes by chromosomal rearrangements.

Case numbers for a randomized clinical trial of boron neutron capture therapy for Glioblastoma multiforme

Boron neutron capture therapy (BNCT) with Na2B12H11SH (BSH) or p-dihydroxyborylphenylalanine (BPA), and with a combination of both, was compared to radiotherapy with temozolomide, and the number of patients required to show statistically significant differences between the treatments was calculated. Whereas arms using BPA require excessive number of patients in each arm, a two-armed clinical trial with BSH and radiotherapy plus temozolomide is feasible.

Hyperpigmentation in North Sea dab Limanda limanda. I. Spatial and temporal patterns and host effects

Hyperpigmentation is a term describing a specific pigment anomaly affecting common dab Limanda limanda in the North Sea and, less frequently, in adjacent areas, e.g. the English Channel, Irish and Celtic Seas, western Baltic Sea and Icelandic waters. Other North Sea flatfish species are also affected, but at a markedly lower prevalence. The condition is characterised by the occurrence of varying degrees of green to black patchy pigment spots in the skin of the upper (ocular) body side and pearly-white pigment spots in the skin of the lower (abocular) body side. In the course of fish disease monitoring programmes carried out by Germany and the UK (England and Scotland), a pronounced spatial pattern of hyperpigmentation has been detected in the North Sea. An increase in prevalence has been recorded in almost all North Sea areas studied in the past 2 decades. The prevalence recorded in hot spot areas of the condition increased from 5 to >40% between 1988 and 2009. Analysis of the German data indicates that the prevalence and intensity (degree of discolouration) of hyperpigmentation increase with size and age, indicating a temporal progression of the condition with size and age. Intense hyperpigmentation is associated with increased growth (length) and decreased condition factor. Potential causes of the condition (UV-B radiation nutrition, water temperature increase, demographic changes) and, in particular, of the spatial/temporal patterns recorded as well as the relationship to host-specific factors (sex, age, length, growth, condition factor) are discussed.

A pragmatic proposal for permissible limits in external quality assessment schemes with a compromise between biological variation and the state of the art

Permissible limits for internal and external quality assurance are either based on biological variation or on the state of the art (technical feasibility). The former approach has a scientific basis, but, in some cases, leads to limits which are either not achievable under the present technology, or which are not stringent enough. If proficiency testing is mandatory, stringent limits which cannot be fulfilled by the majority of laboratories could lead to juristic consequences. Therefore, most national guidelines were based on the state of the art, however, without providing the underlying reasoning. A simple algorithm for permissible limits in external quality assessment schemes (EQAS) is proposed based on biological variation, technical feasibility and correlated to the rate of false positive results. The proposed limits are compared with some limits from several EQAS (RiliBÄK, SEKK, RCPA, CLIA, PROLARIT). The suggested limits are slightly more stringent than the German RiliBÄK, less stringent than the Australasian guidelines and agreed best with the Czech SEKK and the Italian PROLARIT scheme. The graphical presentation of permissible limits strictly derived of biological variation with the proposed limits led to straight lines with different slopes and a cross-over at the limits for quantities with a medium biological variation (e.g., trijodthyronine). The greatest discordance between the various recommendations was observed for calcium, chloride, hemoglobin A

Fibroid explants reveal a higher sensitivity against MDM2-inhibitor nutlin-3 than matching myometrium

Background

Spontaneous cessation of growth is a frequent finding in uterine fibroids. Increasing evidence suggests an important role of cellular senescence in this growth control. Deciphering the underlying mechanisms of growth control that can be expected not only to shed light on the biology of the tumors but also to identify novel therapeutic targets.

Methods

We have analyzed uterine leiomyomas and matching normal tissue for the expression of p14^Arf and used explants to see if reducing the MDM2 activity using the small-molecule inhibitor nutlin-3 can induce p53 and activate genes involved in senescence and/or apoptosis. For these studies quantitative real-time RT-PCR, Western blots, and immunohistochemistry were used. Statistical analyses were performed using the student's t test.

Results

An in depth analysis of 52 fibroids along with matching myometrium from 31 patients revealed in almost all cases a higher expression of p14^Arf in the tumors than in the matching normal tissue. In tissue explants, treatment with the MDM2 inhibitor nutlin-3 induced apoptosis as well as senescence as revealed by a dose-dependent increase of the expression of BAX as well as of p21, respectively. Simultaneously, the expression of the proliferation marker Ki-67 drastically decreased. Western-blot analysis identified an increase of the p53 level as the most likely reason for the increased activity of its downstream markers BAX and p21. Because as a rule fibroids express much higher levels of p14^Arf, a major negative regulator of MDM2, than matching myometrium it was then analyzed if fibroids are more sensitive against nutlin-3 treatment than matching myometrium. We were able to show that in most fibroids analyzed a higher sensibility than that of matching myometrium was noted with a corresponding increase of the p53 immunopositivity of the fibroid samples compared to those from myometrium.

Conclusions

The results show that uterine fibroids represent a cell population of advanced cellular age compared to matching myometrium. Moreover, the data point to members of the p53-network as to potential novel therapeutic targets for the treatment of uterine fibroids.

Decrease in thyroid adenoma associated (THADA) expression is a marker of dedifferentiation of thyroid tissue

Background

Thyroid adenoma associated (THADA) has been identified as the target gene affected by chromosome 2p21 translocations in thyroid adenomas, but the role of THADA in the thyroid is still elusive. The aim of this study was to quantify THADA gene expression in normal tissues and in thyroid hyper- and neoplasias, using real-time PCR.

Methods

For the analysis THADA and 18S rRNA gene expression assays were performed on 34 normal tissue samples, including thyroid, salivary gland, heart, endometrium, myometrium, lung, blood, and adipose tissue as well as on 85 thyroid hyper- and neoplasias, including three adenomas with a 2p21 translocation. In addition, NIS (sodium-iodide symporter) gene expression was measured on 34 of the pathological thyroid samples.

Results

Results illustrated that THADA expression in normal thyroid tissue was significantly higher (p < 0.0001, exact Wilcoxon test) than in the other tissues. Significant differences were also found between non-malignant pathological thyroid samples (goiters and adenomas) and malignant tumors (p < 0.001, Wilcoxon test, t approximation), anaplastic carcinomas (ATCs) and all other samples and also between ATCs and all other malignant tumors (p < 0.05, Wilcoxon test, t approximation). Furthermore, in thyroid tumors THADA mRNA expression was found to be inversely correlated with HMGA2 mRNA. HMGA2 expression was recently identified as a marker revealing malignant transformation of thyroid follicular tumors. A correlation between THADA and NIS has also been found in thyroid normal tissue and malignant tumors.

Conclusions

The results suggest THADA being a marker of dedifferentiation of thyroid tissue.

Permissible performance limits of regression analyses in method comparisons

Method comparisons are indispensable tools for the extensive validation of analytic procedures. Laboratories often only want to know whether an established procedure (x-method) can be replaced by another one (y-method) without interfering with diagnostic purposes. Then split patients' samples are analyzed more or less simultaneously with both procedures designed to measure the same quantity. The measured values are usually presented graphically as a scatter or difference plots. The two methods are considered to be equivalent (comparable) if the data pairs scatter around the line of equality (x=y line) within permissible equivalence lines. It is proposed to derive these limits of permissible imprecision limits which are based on false-positive error rates. If all data pairs are within the limits, both methods lead to comparable false error rates. If one or more data pairs are outside the permissible equivalence limits, the x-method cannot simply be replaced by the y-method and further studies are required. The discordance may be caused either by aberrant values (outliers), non-linearity, bias or a higher variation of e.g., the y-values. The spread around the line of best fit can detect possible interferences if more than 1% of the data pairs are outside permissible spread lines in a scatter plot. Because bias between methods and imprecision can be inter-related, both require specific examinations for their identification.

Indirect reference intervals of plasma and serum thyrotropin (TSH) concentrations from intra-laboratory data bases from several German and Italian medical centres

BACKGROUND

The dogma of establishing intra-laboratory reference limits (RLs) and their periodic review cannot be fulfilled by most laboratories due to the expenses involved. Thus, most laboratories adopt external sources for their RLs, often neglecting the problems of transferability. This is particularly problematic for analytes with a large diversity of existing RLs, as for example thyrotropin (TSH). Several attempts were taken to derive RLs from the large data pools stored in modern laboratory information systems. These attempts were further developed to a more sophisticated indirect procedure. The new approach can be considered a combined concept because it pre-excludes some subjects by direct criteria a-posterior. In the current study, the applicability of the new concept for modern protein bindings assays was examined for estimating RLs of serum and plasma TSH with data sets from several German and Italian laboratories.

METHODS

A smoothed kernel density function was estimated for the distribution of the total mixed data of the sample group (combined data of non-diseased and diseased subjects). It was assumed that the "central" part of the distribution of all data represents the non-diseased ("healthy") population. The central part was defined by truncation points using an optimisation method, and was used to estimate a Gaussian distribution of the values of presumably non-diseased subjects after Box-Cox transformation of the empirical data. This distribution was now considered as the distribution of the non-diseased subgroup. The percentiles of this parametrical distribution were calculated to obtain RLs.

RESULTS

RLs determined by the indirect combined decomposition technique led to similar RLs as found by several recent study reports using a direct method according to international recommendations. Furthermore, the RLs obtained from 13 laboratories in two different European regions reflected the well-known differences of various analytical procedures. Stratification for gender and age was necessary in contrast to earlier reports. With increasing age, an increase of the upper RL and the reference range was observed. Hospitalisation also affected the RLs. Common RLs appeared acceptable only within the same analytical systems. Some laboratories used RLs which were not appropriate for the population served.

CONCLUSIONS

The proposed strategy of combining exclusion criteria with a resolution technique led to retrospective RLs from intra-laboratory data pools for TSH which were comparable with directly determined RLs. Differences between laboratories were due primarily to the well-known bias of the different analytical procedures and to the status of the population.

Observed, unknown distributions of clinical chemical quantities should be considered to be log-normal: a proposal

The distribution of many quantities in laboratory medicine are considered to be Gaussian if they are symmetric, although, theoretically, a Gaussian distribution is not plausible for quantities that can attain only non-negative values. If a distribution is skewed, further specification of the type is required, which may be difficult to provide. Skewed (non-Gaussian) distributions found in clinical chemistry usually show only moderately large positive skewness (e.g., log-normal- and χ(2) distribution). The degree of skewness depends on the magnitude of the empirical biological variation (CV(e)), as demonstrated using the log-normal distribution. A Gaussian distribution with a small CV(e) (e.g., for plasma sodium) is very similar to a log-normal distribution with the same CV(e). In contrast, a relatively large CV(e) (e.g., plasma aspartate aminotransferase) leads to distinct differences between a Gaussian and a log-normal distribution. If the type of an empirical distribution is unknown, it is proposed that a log-normal distribution be assumed in such cases. This avoids distributional assumptions that are not plausible and does not contradict the observation that distributions with small biological variation look very similar to a Gaussian distribution.

HMGA2 and the p19Arf-TP53-CDKN1A axis: a delicate balance in the growth of uterine leiomyomas

Pathogenetically, uterine leiomyomas (ULs) can be interpreted as the result of a monoclonal abnormal proliferation of myometrial cells. Oncogene-induced senescence (OIS) is a frequent phenomenon in premalignant lesions that leads to a growth arrest mainly by the activation of two potent growth-inhibitory pathways as represented by p16(Ink4a) and p19(Arf). The relevance of OIS for the development of UL has not been addressed, but HMGA2, encoded by a major target gene of recurrent chromosomal abnormalities in UL, has been implicated in the repression of the Ink4a/Arf (CDKN2A) locus. This prompted us to examine if HMGA2 contributes to the growth of leiomyomas by repressing this locus. Contrary to the expectations, we were able to show that generally ULs express significantly higher levels of p19(Arf) mRNA than myometrium and that UL with 12q14 approximately 15 rearrangements showed higher expression levels than UL with other cytogenetic aberrations. Furthermore, the finding of a significant correlation between the expressions of p19(Arf) and CDKN1A shows that p19(Arf) triggers senescence rather than apoptosis in UL. Furthermore, the expression levels of HMGA2, p19(Arf), and CDKN1A were found to be correlated with the size of the tumors, indicating that an enhanced growth potential is counterbalanced by the p19(Arf) pathway. Mechanistically, the UL may thus execute a program already present in their cell of origin, where it is activated to protect the genome, for example, in the case of enhanced proliferation. In summary, the results identify the p19(Arf)-TP53-CDKN1A pathway as a major player in the growth control and genomic stability of uterine fibroids.

Reference limits of plasma and serum creatinine concentrations from intra-laboratory data bases of several German and Italian medical centres: Comparison between direct and indirect procedures

BACKGROUND

The current dogma of establishing intra-laboratory reference limits (RLs) and their periodical reviewing cannot be fulfilled by most laboratories due to the expenses involved. Thus, most laboratories adopt external sources for their RLs often neglecting the problems of transferability. Therefore, several attempts were undertaken to derive RLs from the large data pools stored in modern laboratory information systems. These attempts were further developed to a more sophisticated indirect procedure. The new model can be considered a combined approach because it pre-excludes some subjects by direct criteria. In the current study, the new concept was applied to estimate RLs for serum and plasma creatinine from several German and Italian laboratories.

METHODS

A smoothed kernel density function was estimated for the distribution of the total mixed data of the sample group (combined data of non-diseased and diseased subjects). It was assumed that the "central" part of the distribution of all data represents the non-diseased ("healthy") population. The central part was defined by truncation points using an optimisation method, and was used to estimate a Gaussian distribution of the values of presumably non-diseased subjects after Box-Cox transformation of the empirical data. This distribution was now considered as the distribution of the non-diseased subgroup. The percentiles of this parametrical distribution were calculated to obtain RLs.

RESULTS

RLs determined by the indirect combined decomposition technique led to similar RLs as the classical direct method. Furthermore, the RLs obtained from 14 laboratories in 2 different European regions reflected the well-known differences of various analytical procedures. Stratification for gender and age was necessary. With rising age, an increase of the upper RL and of the reference range was observed. Hospitalization appeared also to affect the RLs. The new approach led to RLs in an artificially mixed population of diseased and non-diseased subjects (selected by clinical criteria) which were identical to RLs determined by a direct method applied to the non-diseased subgroup.

CONCLUSIONS

The proposed strategy of combining exclusion criteria with a resolution technique led to plausible retrospective RLs from intra-laboratory data pools for creatinine. Differences between laboratories were mainly due to the well-known bias of the different analytical procedures.

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

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

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

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

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