Graphical interpretation of confidence curves in rankit plots

Separating disease and health for indirect reference intervals

The indirect approach to defining reference intervals operates ‘a posteriori’, on stored laboratory data. It relies on being able to separate healthy and diseased populations using one or both of clinical techniques or statistical techniques. These techniques are also fundamental in a priori, direct reference interval approaches. The clinical techniques rely on using clinical data that is stored either in the electronic health record or within the laboratory database, to exclude patients with possible disease. It depends on the investigators understanding of the data and the pathological impacts on tests. The statistical technique relies on identifying a dominant, apparently healthy, typically Gaussian distribution, which is unaffected by the overlapping populations with higher (or lower) results. It depends on having large databases to give confidence in the extrapolation of the narrow portion of overall distribution representing unaffected individuals. The statistical issues involved can be complex, and can result in unintended bias, particularly when the impacts of disease and the physiological variations in the data are under appreciated.

High-throughput genotyping of copy number variation in glutathione S-transferases M1 and T1 using real-time PCR in 20,687 individuals

OBJECTIVES

Characteristic for the genes encoding glutathione S-transferase (GST) M1 and GSTT1 is a null allele, suggested to increase susceptibility to chronic diseases. We report an optimized method for the determination of copy number variation (CNV) in GST genes.

DESIGN AND METHODS

Real-time multiplex PCR reactions were optimized for quantification of GSTM1 and GSTT1 CNV using the DeltaCt method, a fixed volume of diluted DNA, a total volume of 10 microL, 384-well formats, and single determinations of each sample.

RESULTS

Consistent genotyping was obtained using DNA in a range of 0.41 ng to 100 ng. In a general population sample of 20,687 individuals the genotype frequencies were concordant with other methods used as standards. Throughput was 4600 genotypes per day at a reagent price of 0.5 euros per sample.

CONCLUSIONS

This high-throughput, low cost method accurately determines CNV in the GST genes enabling reliable estimates of disease prediction in large epidemiological samples.

Visceral and subcutaneous adipose tissue assessed by magnetic resonance imaging in relation to circulating androgens, sex hormone-binding globulin, and luteinizing hormone in young men

CONTEXT

No large studies of young men have examined circulating sex hormones in relation to visceral and sc adipose tissues.

OBJECTIVE

The aim of this study was to investigate the role of visceral adipose tissue and sc adipose tissue on circulating sex hormones and the impact of obesity on sex hormone reference intervals.

DESIGN, SETTING, AND PARTICIPANTS

Population-based study of 783 Danish 20- to 29-yr-old men was performed using dual-energy x-ray absorptiometry in all men and magnetic resonance imaging in 406 men.

MAIN OUTCOME MEASURES

Total, bioavailable, and free testosterone, dihydrotestosterone (DHT), total and bioavailable estradiol, SHBG, and LH were measured.

RESULTS

In multiple regressions, visceral adipose tissue was an independent, inverse correlate of bioavailable and free testosterone. Subcutaneous adipose tissue correlated negatively with SHBG and positively with bioavailable estradiol adjusted for total testosterone. Both visceral adipose tissue and sc adipose tissue correlated inversely with total testosterone and DHT. Adjusting for SHBG, only visceral adipose tissue remained significantly correlated. Low total testosterone in viscerally obese men was not accompanied by increased LH. The androgen reference intervals were significantly displaced toward lower limits in obese vs. nonobese men (total testosterone: 8.5-29.3 vs. 12.5-37.6 nmol/liter; bioavailable testosterone: 6.1-16.9 vs. 7.6-20.7 nmol/liter; free testosterone: 0.23-0.67 vs. 0.29-0.78 nmol/liter; and DHT: 0.63-2.5 vs. 0.85-3.2 nmol/liter), whereas total estradiol (36.5-166 pmol/liter) and bioavailable estradiol (23.4-120 pmol/liter) reference intervals were not. In obese men, 22.9% had total testosterone less than 12.5 nmol/liter.

CONCLUSIONS

Visceral adipose tissues correlate independently with bioavailable and free testosterone in young men. The inverse relationship between total testosterone and sc adipose tissue seems to be accounted for by variations in SHBG. The reference intervals for total testosterone, bioavailable testosterone, free testosterone, and DHT are displaced toward lower limits in obese men.

A plea for intra-laboratory reference limits. Part 1. General considerations and concepts for determination

Accurate results for quantitative procedures can be useless if the reference limits for the interpretation of laboratory results are unreliable. Recent concepts for quality management systems require that laboratories pay more attention to identification and verification of reference limits. Scientific recommendations often claim that each laboratory should determine intra-laboratory reference limits, which should be reviewed periodically. This recommendation is currently neglected by most laboratories; instead they use reference limits from external sources, despite various problems of transference. Prospective and retrospective methods either using or neglecting disease prevalences (polymodal or unimodal concepts, respectively) and applying different statistical approaches for determining reference limits have been described. The various procedures are reviewed with regard to their diagnostic sensitivity, specificity and (non-)efficiency. The present gold standard is the reference limit concept according to IFCC recommendations (a unimodal prospective approach). This concept, together with trueness-based standardization, is the most useful basis for harmonization of the decision-making process with laboratory results, despite complex problems of traceability and transference. This harmonization is at present only achieved for a limited number of analytes for which SI units and traceability can be technically realized. For the majority of measurands in laboratory medicine, much research is still required and results cannot be expected in the near future. For these measurands, a need remains for internal, efficient and simple identification of population-based reference limits. Therefore, newer retrospective concepts were developed that use large data sets from laboratory information systems to derive intra-laboratory reference limits. These approaches appear promising and should be further developed.

Managing transferability of laboratory data

Considerable attention has been focused on definition and enhancement of the analytical quality in laboratory testing over the past decades. Advances in laboratory technology and computer informatics have allowed a major sense of confidence with the analytical phase and more efforts should now be focused on extra-analytical areas of improvement, that should further strengthen the link between cost effectiveness and clinical outcome. Deduction and implementation of common reference intervals, to be possibly shared by a regional network of clinical laboratories, appear so far a crucial step to increase efficiency and harmonization. With the experience gained from External Quality Control exercises and with the consensus of several contributory laboratories, this process is underway in Italy. Quality performances resulting from widespread implementation of common reference intervals and longitudinal comparison of patient's data, will allow clinical laboratories to accomplish with a major transferability, amplifying health benefits and meeting increasing health systems demand.

Creation of a low-risk reference group and referenceinterval of fasting venous plasma glucose

Reference intervals are recommended for naturally occurring quantities and required in the evaluation of new components in order to provide clinically useful information.

The aim of the present study is to present a method for selecting reference individuals for the determination of fasting venous plasma glucose (f-vPG) reference intervals and ways to determine if disease groups can share reference intervals with an ideal reference population.

Reference subjects were randomly selected, eligibility was judged according to predetermined inclusion and exclusion criteria. Using the literature we selected risk indicators for diabetes mellitus (DM) and used these indicators to rule out high-risk individuals in order to obtain a reference distribution of f-vPG determined using individuals with low risk of DM. The distributions of f-vPG in the high-risk individuals was compared with that determined for the low-risk group. We then estimated the ability of the high-risk individuals to share the reference interval of the low risk individuals, and calculated the fraction that was outside this interval. Distributions were also investigated for linearity in the cumulated frequency rankit distribution of ln-values. The allowable difference between two reference limits could not exceed 0.375 times the population biological variation.

Most risk indicators were powerful predictors of high f-vPG values. Subgroups with these risk indicators should not be included in the homogeneous ln-normally distributed reference distribution. Distributions of f-vPG concentrations in individuals with risk factors were not homogeneous and varying percentages of individuals were outside the reference distribution, having f-vPG greater than 7.0 mmol/l.

We conclude that randomisation is only useful to recruit candidate reference subjects. To rule out subjects according to clinical risk factors for diabetes, it is necessary to identify a reference population with low risk of exhibiting increased f-vPG concentrations. This method may be used to validate a reference interval for a particular analyte with respect to an investigated disease, and to stratify risk factors of importance.

Reference intervals for plasma proteins: similarities and differences between adult Caucasian and Asian Indian males in Yorkshire, UK

The aim of this study was to investigate similarities and differences in the distribution of serum concentrations of nine proteins in two racial groups (Caucasian and Asian Indian) of adult males living in the same geographical area (Leeds, Bradford, UK) for at least two generations. This is part of a larger study to determine the need for separating reference intervals for racial and ethnic groups worldwide. The distributions of concentrations for all proteins evaluated in the Indians fit ln-Gaussian distributions, indicating probable homogeneity. However, for the Caucasians, the distributions for α