Analytical quality goals and assessment to ensure transferability of laboratory results.

About 3 years ago NORDKEM started a project entitled 'Medical Need for Quality Specifications in Clinical Laboratories'. This communication describes the general approach of this project and a subproject oriented towards problems of transferability of clinical laboratory data. Attempts are made to estimate clinical goals for analytical measurements--either used alone or in combinations with other measurements or observations--in defined clinical situations. Various methodologies are used for the assessment of the clinical goals, starting, e.g., from clinical situations or biological reference data. The analytical quality specifications are expressed as total allowable errors. It is necessary to complement specifications of 'clinical goals' with data describing characteristics of the measurement procedure, preanalytical errors and internal and external quality assurance procedures in order to establish the laboratory quality specification guaranteed by the laboratory. Problems of transferability of clinical laboratory results occur both within a laboratory/hospital and between laboratories/hospitals/health care units, problems that sometimes make communication of laboratory results difficult or even meaningless. In order to study the transferability of clinical laboratory data within a health care region, so called 'transformation functions' could be used to characterize each laboratory in a strict quality assessment/proficiency testing procedure on the basis of analytical quality specifications. Under certain conditions, e.g. for analytical procedures with high specificity and documented stable analytical performance, numerical correction of analytical bias could be performed to decrease interlaboratory variation to a level specified by medical needs.

A systematic study of nucleotide analysis of human erythrocytes using an anionic exchanger and HPLC.

A two-step procedure for rapid HPLC analysis of nucleotides from human erythrocytes is described. A strong anion exchanger Partisil-10 is used as column material. Elution of monophosphates requires about 12 min and the elution of di- and triphosphates 21 min. The elutions are performed separately and with different injections as such a procedure will save time otherwise used to re-condition the columns. In addition to the three adenylates other nucleotides such as GTP, GDP, IMP and NAD can be recorded as isolated, well-defined peaks, which can be subject to quantitative analysis. The mean value of ATP concentration for 12 healthy individuals was 1.55 +/- 0.05 mmol/l, about 25% higher than generally reported in the literature. Accurate estimates of ADP and AMP concentrations allowed calculation of mean values for the physiologically interesting ratios: adenylate energy charge (0.945 +/- 0.002) and equilibrium constant for adenylate kinase (1.205 +/- 0.053). GDP and GTP are present in concentrations that are about 4% of those for corresponding adenylates. The analysis of nucleotides in human erythrocytes is a useful way of studying erythrocyte preservation and investigating patients with hemolytic disorders.

Erythrocyte nucleotide pattern in two children in a Norwegian family with pyrimidine 5'-nucleotidase deficiency.

In the erythrocytes from two Norwegian children, a brother and a sister, with a hemolytic anemia due to pyrimidine 5'-nucleotidase deficiency, the pyrimidine and purine nucleotides have been investigated using HPLC with a strong anionic exchanger. The standard procedure was complemented with some additional elution systems which made it feasible to separate in the extract and to analyse, in addition to the conventional mono-, di- and triphosphates, UDP-glucose, UDP-N-acetylglucosamine, CDP-choline and CDP-ethanolamine. The two different purine nucleotides (A, G) and the two different pyrimidine nucleotides (U, C) exhibited normal ratios (energy charge ratios) between the conventional nucleotides. This would indicate that the erythrocytes have a sufficient energy production. It is suggested that the partly intravascular hemolysis might be due to disturbed synthesis of phospholipids.

Purine metabolism in normal and ITP-pyrophosphohydrolase-deficient human erythrocytes.

Fresh and stored erythrocytes from normal and ITP-pyrophosphohydrolase (ITP-ase, EC 3.6.1.19) deficient individuals were incubated with hypoxanthine, guanine, allopurinol, and inosine. Differences in the purine metabolism between the normal and the ITP-ase deficient erythrocytes were observed only in the IMP-ITP cycle. Hypoxanthine, guanine and allopurinol were converted to nucleotides at the same rate. Hypoxanthine (2.5 mumol/l) inhibited the salvage of allopurinol (40 mumol/l). A slow decrease (0.7%/day) in salvage rate was observed in both types of cells upon storage at +4 degrees C. Erythrocyte ITP-ase activity was measured in a reference sample group of 48 healthy volunteers. Two distinct groups were found with mean activities equal to 48.3 +/- 13.1 nkat/g Hb (means +/- SD, n = 38) and 11.4 +/- 4.3 nkat/g Hb (n = 10). In two previously selected subjects, the ITP-ase activity was 0.2 and 2.4 nkat/g Hb. A hypothetical genetic mechanism is discussed. The maximal energy turnover in the IMP-ITP cycle during hypoxanthine incubation was found to be less than 10% of the basal erythrocyte energy turnover.

The influence of analytical bias on diagnostic misclassifications.

Quality specifications for analytical imprecision and bias based on the state of the art; 'biology' and 'analysis of clinical situations' have been proposed by several scientists. Most interesting is the assessment of 'diagnostic misclassifications' based on direct evaluation of the consequences of analytical bias on the percentage of false positives and false negatives from a clinical decision situation, or based on the percentage of healthy individuals outside each reference limit when common reference intervals are used. With use of graphical or computer simulations assuming increasing (positive or negative) analytical bias, the expected percentage of misclassifications can be estimated- and, for the error for which the outcome (the fraction of misclassifications) is considered unacceptable, the maximum allowable analytical bias can be defined. An overview is given of previous proposals for specification of allowable analytical bias, and new examples are presented: (i) for S-transferrin. an analytical bias of +10% will increase the percentage of healthy individuals with measured concentration values above the upper reference limit from 2.5 to 10% (ii) the percentage of healthy men with concentration values for S-cholesterol above 6.2 mmol/l (240 mg/dl) will vary between 25 and 85% for analytical bias from - 1.0 to +1.0 mmol/l (+/- 16%): (iii) for glycated haemoglobin, two examples are given which illustrate the effect of analytical bias on the risk of retinopathy and so-called 'microalbuminuria' for measured values identical to the target 7.5% and 10.1% glycated haemoglobin, respectively. It is concluded that analytical bias may have significant impact on diagnostic performance, better standardization is needed, and quality specifications for allowable analytical bias should be based on medical usefulness criteria or, if such data are not available, on biological criteria.

Between-country comparability of clinical chemistry results: an international quality assessment survey of 17 analytes in six European countries through existing national schemes.

Two lyophilized control sera were distributed through seven national external quality assessment schemes in six European countries--Belgium, Switzerland, France, The Netherlands, Sweden and the United Kingdom--participated in the study. The results for 17 routine analytes were obtained from almost 5000 laboratories for the two sera. The organizers of the schemes were asked to process the results according to a common outlier removal procedure, and submit method-related data if available. The two sera were also distributed through the external/internal scheme of The Netherlands, and the within-laboratory standard deviations calculated in this scheme have been used in a scaling procedure for the external mean values and between-laboratory standard deviations of the participating countries. The results show remarkable agreement in the national mean values for practically all analytes, but considerable differences in the between-laboratory variation. Data from comparable method groups was obtained for 12 analytes from Belgium, France, The Netherlands and the UK. Though revealing some specific differences between methods and countries, the method-related data are generally in agreement with the all-method data. In this study reference method values were only available for cholesterol. The high degree of agreement found suggests, however, that mutual recognition of all-method mean values in national schemes could be acceptable, especially for analytes for which reliable reference methods are not available. The major element of variation is between-laboratory rather than between-country.

Substance rates of different steps of purine metabolism in normal and preserved red blood cells (RBC) studied in experiments simulating in vivo conditions.

A dialysis incubation system simulating the conditions in the circulation can be used: To draw conclusions about the RBC in transporting purines between organs. To improve solutions for "rejuvenating" stored RBC. To design better systems for quality control of stored RBC.

Pancreatic iso-amylase in serum as a diagnostic test in different clinical situations. A simulation study.

The potential use of a pancreatic iso-amylase test has been studied by computer simulation. This simulation was performed to assess the quality requirements on the test in different clinical situations. It was shown that, in most situations studied, an optimal discriminating level and an optimal analytical quality (imprecision and bias) could be established. In one situation studied in more detail, it was found that the influence of pre-analytical variation, duplicate determinations, reclassification of borderline cases and size of reference sample groups were of minor importance. The weighting ratio of false negatives: false positives was found to be critical for the results. It is concluded that a simulation study of this type can be recommended prior to entering the phases of analytical refinement and clinical testing on patients.

Medical need for quality specifications--a NORDKEM project for selecting the appropriate quality in clinical laboratories.

The Nordic Clinical Chemistry Project (NORDKEM) has during its existence run several projects dealing with analytical quality requirements and the specifications of such requirements. The latest project-"Medical Need for Quality Specifications in Laboratory Medicine"-started three years ago and is now to be reported. The project consists of three main subprojects and a large number of associated projects. The main subprojects deal with: *External quality assurance for proteins (Per Hyltoft Petersen et al.) *Transferability of clinical laboratory data (Torgny Groth & C-H de Verdier) *Terminology (René Dybkaer) "Clinical goals" are assessed using different kinds of procedures. Comparison with the characteristics of "the analytical procedures" and "the quality assurance programs" gives the Management of the clinical laboratory a background for determining the "analytical quality specifications" of the laboratory. Procedures for setting up clinical goals and analytical quality specifications are given and they are further exemplified in the associated projects. Clinical goals and the analytical quality specifications are expressed and calculated in similar ways as total allowable error (TEa), as a coefficient of variation or an absolute error within defined concentration intervals.

Principles for developing improved quality control procedures.

Achieving quality goals in the clinical chemistry laboratory requires a comprehensive understanding of the many critical components and factors that are involved in a quality assurance program. The present paper has therefore been divided into sections dealing with quality goals as a rational starting point, determinants of quality for an analytical procedure, assessing the quality of a measurement procedure, assessing the quality of an internal control procedure, improving the quality of internal control procedures, designing an internal control procedure to provide a specified level of quality, strategy for implementing high power control procedures, implications of frequency of errors and predictive value theory on design of control procedures, role of external quality assessment in achieving quality goals, tools needed to improve quality control, and further considerations in achieving quality goals. In designing control procedures we have focused mainly on internal statistical control, emphasizing the new aspects of frequency of analytical disturbances. Less detailed consideration has been given to external quality assessment, though this problem area is also essential to a quality assurance program. Many other aspects have not been discussed, e.g., requirements for control materials, and use of patient specimens for control purposes, though both aspects are obviously very important. Even with these limitations, we think that quality control can be improved by development of better control procedures following the principles outlined here.

Data base management systems for evaluation of analytical procedures.

The present paper gives a short introduction to data base management systems, and their application in the clinical laboratory for evaluating the quality of analytical procedures. Two applications based on the MIMER relational data base management system are described in some detail: An internal quality control data base under development at the clinical chemistry laboratory of the University Hospital in Uppsala, and a data base system for external quality assessment developed in a previous NORDKEM project.

Present analytical quality in the Nordic clinical chemistry laboratories.

An introductory review is given of the discussion in the Nordic countries on the definition, aim, and optimal organization of quality control. Published and unpublished Scandinavian works have been reviewed and commented under the following headlines: common chemical analyses, enzyme analyses, serum and plasma protein analyses, hormone analyses, drug analyses, hematological tests, and urine analyses. It is concluded that methods for calculating medical standards of analytical quality in clinical chemistry form the logical background for the design of an optimal quality control system, which will guarantee that analytical results well have a specified probability of satisfying the medical requirements.

Assessment of analytical quality in Nordic clinical chemistry laboratories using data from contemporary national programs.

The aim of this investigation was primarily to assess analytical quality expressed as between-laboratory, within-laboratory, and total imprecision, not in order to detect laboratories with poor performance, but in the positive sense to provide data for improving critical steps in analytical methodology. The aim was also to establish the present state of the art in comparison with earlier investigations to see if improvement in analytical quality could be observed.

A quality manual for the clinical laboratory including the elements of a quality system. Proposed guidelines.

Development of quality manuals is a means for the promotion of quality in clinical laboratories by describing the total quality system. It also provides opportunity of checking whether the quality system is implemented in reality and demonstrates to the hospital administration and the clinicians that the laboratory is committed to quality. The intention of these guidelines is to describe the elements of the quality system for a large clinical laboratory, and to present such a system in the form of a quality manual. The proposed guidelines comply, where relevant, with ISO/IEC guide 25 'General requirements for the technical competence of testing laboratories' and EN 45001 'General criteria for the operation of testing laboratories'. The document may be used as an aid for laboratories wishing to be accredited according to EN 45001, or intending to apply for formal certification of their quality systems, according to ISO 9001 'Quality systems--Model for quality assurance in design/development, production, installation, and servicing' utilizing ISO 9004 'Quality management and quality system elements--guidelines; Part 2 Guidelines for service'. However, information about the minimum requirements for official recognition should be obtained from the particular accreditation or certification body concerned.