Per Hyltoft Petersen

Defining analytical performance specifications: Consensus Statement from the 1st Strategic Conference of the European Federation of Clinical Chemistry and Laboratory Medicine.

*Corresponding author: Sverre Sandberg, Norwegian Quality Improvement of Primary Care Laboratories (Noklus), Institute of Global Public Health and Primary Health Care, University of Bergen and Laboratory of Clinical Biochemistry, Bergen, Norway, E-mail: sverre.sandberg@isf.uib.no Callum G. Fraser: Centre for Research into Cancer Prevention and Screening, University of Dundee, Ninewells Hospital and Medical School, Dundee, Scotland, UK Andrea Rita Horvath: SEALS Department of Clinical Chemistry, Prince of Wales Hospital, Screening and Test Evaluation Program, School of Public Health, University of Sydney, and School of Medical Sciences, University of New South Wales, Sydney, NSW, Australia Rob Jansen: Netherlands Foundation for Quality Assessment of Medical Laboratories (SKML), Radboud University, Nijmegen, The Netherlands Graham Jones: SydPath, St Vincent’s Hospital, Sydney, NSW, Australia Wytze Oosterhuis: Atrium-Orbis, Department of Clinical Chemistry and Haematology, Heerlen, The Netherlands Per Hyltoft Petersen: Norwegian Quality Improvement of Primary Care Laboratories (Noklus), Institute of Global Public Health and Primary Health Care, University of Bergen, Norway Heinz Schimmel: European Commission, Joint Research Centre, Institute for Reference Materials and Measurements (IRMM), Geel, Belgium Ken Sikaris: Sonic Healthcare and Melbourne University, Melbourne, Vic, Australia Mauro Panteghini: Centre for Metrological Traceability in Laboratory Medicine (CIRME), University of Milan, Milan, Italy Consensus Statement

Establishment of a serum thyroid stimulating hormone (TSH) reference interval in healthy adults. The importance of environmental factors, including thyroid antibodies

Abstract It has previously been shown that thyroid antibodies affect thyroid stimulating hormone (TSH) concentrations in men and women and that TSH levels are predictive of future thyroid disease. We investigated the validity of the National Academy of Clinical Biochemistry (NACB) guidelines regarding the TSH reference interval by studying 1512 individuals. Two hundred and fifty had at least one thyroid antibody, 121 were taking medications other than estrogens and occasional analgesics, and 105 reported a family history of thyroid disease. Serum TSH, thyroid peroxidase antibodies (TPOab) and thyroglobulin antibodies (Tgab) were determined on AutoDELFIA and TSHRab by a radioreceptor assay (RRA) from Brahms Diagnostica. For individuals without thyroid antibodies and other risk factors, no effect of age and gender was seen for serum TSH. Neither medication nor the presence of Tgab alone had any influence on serum TSH. TPOab alone or in combination with Tgab were associated with an increased serum TSH level. The ‘cumulative percentage distributions’ of subgroups, as well as the combined population, was ln-Gaussian distributed. The central 95% of the population was within the 95% CI in rankit-plots. Consequently, a common reference interval for serum TSH of 0.58–4.07 mIU/l for all adults between 17 and 66 years of age was established. This reference interval is much higher than expected from the NACB-guidelines.

Relative importance of genetic effects in rheumatoid arthritis: historical cohort study of Danish nationwide twin population

Abstract Objective: To determine the relative importance of environmental and genetic effects in the development of rheumatoid arthritis. Design: Historical cohort study with record linkage between a twin registry and the Danish discharge registry as well as the Danish national registry of deaths used to estimate completeness. Setting: Two population based nationwide twin birth cohorts. Participants: 37 338 twins were sent a questionnaire about rheumatic diseases. Self reported rheumatoid arthritis was verified by clinical examination and from medical records. Main outcome measures: The probandwise concordance rate of rheumatoid arthritis in monozygotic and dizygotic twins. Results: The response rate was 84.7%. Rheumatoid arthritis was verified in 13 monozygotic and 36 dizygotic twins. There were no concordant monozygotic twin pairs and two concordant dizygotic twin pairs. Based on capture-recapture methods the probability of ascertainment was 78.3%. The probandwise concordance rate was 0 (95% confidence interval 0 to 24.7) in monozygotic twins and 8.8 (1.9 to 23.7) in dizygotic twins. Conclusion: Genes are of minor importance in the development of rheumatoid arthritis. What is already known on this topic Rheumatoid arthritis is a multifactorial disease determined by both genetic and environmental factors Previous twin studies have shown a higher concordance for rheumatoid arthritis in monozygotic than in dizygotic twins, but the results have been biased in favour of genetic effects What this paper adds As concordance for rheumatoid arthritis in this study was no more common in monozygotic twins than in dizygotic twins environmental effects may be more important than genetic effects in the development of rheumatoid arthritis

The index of individuality is often a misinterpreted quantity characteristic.

Abstract The concept of the “index of individuality” was introduced by Eugene Harris in 1974. The index of individuality, calculated as (CVA 2 + CVI 2)1/2/CVG, where CvA, CvI, and CvG are analytical, within-subject, and between-subject coefficients of variation respectively, has been used by many to investigate the utility of conventional population-based reference values. For a high index of individuality, >1.4, it has been said that reference intervals will be more useful than for a low index, < 0.6. The validity of these concepts is investigated here and a number of our findings are at odds with the generally held opinion. The index of individuality has no impact on the fraction of individuals classified using population-based reference values, as long as the change in concentration from the usual state is of the same absolute magnitude and one sample is assayed to detect disease. However, when a measurement falling outside a reference limit is repeated in order to verify the finding, the index of individuality has considerable influence. For quantities with very low indices, the repeat test result, will be close to the first and give no new information, whereas for quantities with high indices, a repeat test will decrease the number of true positives and false positives.

Confidence Intervals and Power Calculations for Within-Person Biological Variation: Effect of Analytical Imprecision, Number of Replicates, Number of Samples, and Number of Individuals

BACKGROUND Reliable estimates of within-person biological variation and reference change value are of great importance when interpreting test results, monitoring patients, and setting quality specifications. Little information has been published regarding what experimental design is optimal to achieve the best estimates of within-person biological variation. METHOD Expected CIs were calculated for different balanced designs for a 2-level nested variance analysis model with varying analytical imprecision. We also simulated data sets based on the model to calculate the power of different study designs for detection of within-person biological variation. RESULTS The reliability of an estimate for biological variation and a studys power is very much influenced by the study design and by the ratio between analytical imprecision and within-person biological variation. For a fixed number of measurements, it is preferable to have a high number of samples from each individual. Shortcomings in analytical imprecision can be controlled by increasing the number of replicates. CONCLUSIONS The design of an experiment to estimate biological variation should take into account the analytical imprecision of the method and focus on obtaining the highest possible reliability. Estimates of biological variation should always be reported with CIs.

A Comparison of Analytical Goals for Haemoglobin A1c Assays Derived Using Different Strategies

Analytical goals for the performance characteristics of assays of haemaoglobin A1c (HbA1c) have been investigated using different assumptions for generation of estimates, these being based on strategies using data on biological variation and on the clinical use of results. The derived goals are highly dependent on the assumptions made. In general, in monitoring of patients (using results from the same laboratory), the analytical imprecision is the most demanding, whereas bias (inaccuracy) is the most important characteristic when strategies for several centres (laboratories) to achieve similar results are invoked. Goals for analytical quality should be given in a form in which both analytical imprecision and bias (or systematic error) are specified. When several goals are to be considered (for different relevant assumptions), the most demanding should be used.

Clinical Use of Cancer Biomarkers in Epithelial Ovarian Cancer: Updated Guidelines From the European Group on Tumor Markers.

Objective To present an update of the European Group on Tumor Markers guidelines for serum markers in epithelial ovarian cancer. Methods Systematic literature survey from 2008 to 2013. The articles were evaluated by level of evidence and strength of recommendation. Results Because of its low sensitivity (50–62% for early stage epithelial ovarian cancer) and limited specificity (94–98.5%), cancer antigen (CA) 125 (CA125) is not recommended as a screening test in asymptomatic women. The Risk of Malignancy Index, which includes CA125, transvaginal ultrasound, and menopausal status, is recommended for the differential diagnosis of a pelvic mass. Because human epididymis protein 4 has been reported to have superior specificity to CA125, especially in premenopausal women, it may be considered either alone or as part of the risk of ovarian malignancy algorithm, in the differential diagnosis of pelvic masses, especially in such women. CA125 should be used to monitor response to first-line chemotherapy using the previously published criteria of the Gynecological Cancer Intergroup, that is, at least a 50% reduction of a pretreatment sample of 70 kU/L or greater. The value of CA125 in posttherapy surveillance is less clear. Although a prospective randomized trial concluded that early administration of chemotherapy based on increasing CA125 levels had no effect on survival, European Group on Tumor Markers state that monitoring with CA125 in this situation should occur, especially if the patient is a candidate for secondary cytoreductive surgery. Conclusions At present, CA125 remains the most important biomarker for epithelial ovarian cancer, excluding tumors of mucinous origin.

THYROGLOBULIN OF VARYING MOLECULAR SIZES WITH DIFFERENT DISAPPEARANCE RATES IN PLASMA FOLLOWING SUBTOTAL THYROIDECTOMY

To investigate the possible presence of thyroglobulin (Tg) of different molecular sizes in plasma, blood specimens were drawn from patients during and after surgery for thyroid adenoma. Tg was measured in all serum samples by a radioimmunoassay. Selected samples were fractionated on a sepharose CL‐6B column, and the fractions were assayed for Tg antigen.

Combination of analytical quality specifications based on biological within- and between-subject variation

At a conference on ‘Strategies to Set Global Analytical Quality Specifications in Laboratory Medicine’ in Stockholm 1999, a hierarchy of models to set analytical quality specifications was decided. The consensus agreement from the conference defined the highest level as ‘evaluation of the effect of analytical performance on clinical outcomes in specific clinical settings’ and the second level as ‘data based on components of biological variation’. Here, the many proposals for analytical quality specifications based on biological variation are examined and the outcomes of the different models for maximum allowable combined analytical imprecision and bias are illustrated graphically. The following models were investigated. (1) The Cotlove et al. (1970) model defining analytical imprecision (%CVA) in relation to the within-subject biological variation (%CVw-s) as: %CVA≤ 0·5 × %CVW-S (where %CV is percentage coefficient of variation), (2) The Gowans et al. (1988) concept, which defines a functional relationship between analytical imprecision and bias for the maximum allowable combination of errors for the purpose of sharing common reference intervals. (3) The European Group for the Evaluation of Reagents and Analytical Systems in Laboratory Medicine (EGE Lab) Working Group concept, which combines the Cotlove model with the Gowans concept using the maximal acceptable bias. (4) The External Quality Assessment (EQA) Organizers Working Group concept, which is close to the EGE Lab Working Group concept, but follows the Gowans et al. concept of imprecision up to the limit defined by the model of Cotlove et al. (5) The ‘three-level’ concept classifying analytical quality into three levels: optimum, desirable and minimum. The figures created clearly demonstrated that the results obtained were determined by the basic assumptions made. When %CVW-S is small compared with the population-based coefficient of variation [%CVp = (%CV2 W-S +%CV2 B-S)1/2], the EGE Lab and EQA Organizers Working Group concepts become similar. Examples of analytical quality specifications based on biological variations are listed and an application on external quality control is illustrated for plasma creatinine.

An improved co-precipitation assay for determination of thyroglobulin antibodies

A radioassay for determination of thyroglobulin antibodies in human serum using [125I]thyroglobulin co-precipitated with antihuman IgG is described. Serial dilutions of the antibody containing sera gave nearly rectilinear and parallel logit-log curves in conditions of moderate antigen excess. A secondary standard serum calibrated against the Medical Research Council Research standard A 65/93, which by definition c;ntains 1 Mega unit/1 (MU/1) was used for standardization. The mean imprecision in the concentration range 0.74-241 MU/1 was CV = 3% (within assay) and CV = 8% (total). The detection limit was 0.002 MU/1. The assay was compared to an antigen binding capacity method with an imprecision of 15% (total) and a detection limit of 0.1 MU/1. The coefficient of correlation between the two methods was: R = 0.997 (our method = 0.019 x antigen binding capacity -0.33). Based on this 1 Mega unit was found equivalent to 53 nmol thyroglobulin.