Desirable standards for hematology tests: a proposal

Few analytic goals have been proposed for hematology tests, and these are based upon subjective clinical opinions. It is proposed that the current consensus strategies for delineating analytic goals in clinical chemistry can be validly used in the other disciplines of clinical pathology. Goals for imprecision are best based upon average intraindividual biologic variation; such goals are more stringent than those previously published. There are many cogent reasons that justify the goal for inaccuracy of no bias. In consequence, goals for imprecision should be viewed as goals for total laboratory error. Further experimental work on biologic variation is required to develop a wider range of goals for hematology and coagulation tests, if these strategies are considered worthy of adoption.     

About the choice of acceptability limits in external quality assessment schemes

Quality control schemes are a practical tool used in clinical laboratories and an essential element for any quality assurance process. In France, external quality assessment schemes (EQAS) can be mandatory (as national quality control organized by AFSSAPS) or voluntary as those suggested by French associations (ProBioQual, CTCB or Asqualab). These EQAS usually evaluate participants according to their performances: this ranking depends on acceptability limits which are here compared. Various examples based on ProBioQual's background illustrate difficulties to plan out analytical quality specifications. A comment is given about the best criteria (state of the art or biological variation mainly) to be considered to delimit analytic goals. This discussion includes approaches suggested by French committee on accreditation (Cofrac). All criteria could be criticized but it is important to compare oneself laboratory to peers and also to take account of biological variation.     

Setting quality goals for laboratory tests

The ideal situation with regard to quality assurance in clinical pathology would be that quality goals in numerical format were available for all the practicability and reliability characteristics of laboratory tests, particularly the latter. Many strategies have been used for the setting of quality goals for the most important reliability characteristics, namely, imprecision and bias. These have included fractions of the reference interval, opinions of clinicians, the state of the art, views of expert individuals and groups, the influence of analytical error on clinical utility and biological variation. All of these have advantages and disadvantages. In spite of some interesting recent proposals, quality goals based on biological variation appear to be the best currently available and seem to have led to a consensus among Europeans that, in simple terms:

1. desirable maximum imprecision < one-half the within-subject biological variation,
2. desirable maximum bias < one-quarter the group [within- plus between subject] variation, and
3. maximum difference between methods < one-third the within-subject biological variation. There appears a need for further work in setting quality goals for laboratories which deal with samples from animals; international collaboration has proved productive in human clinical biochemistry and may be worthy of emulation.

     

The concept of establishing vs verifying analytic claims in method evaluations.

The establishment of analytic claims occurs during the method development stage. For commercial methods, the thorough characterization of analytic performance is the responsibility of the manufacturer. The manufacturer establishes performance claims with a high degree of certainty by utilizing statistically sound experimental protocols with sufficient degrees of freedom. The manufacturer should establish performance claims that state the expected performance of the method for the intended spectrum of patients and laboratory environment. The verification of analytic claims occurs by the end-user of the method. The end-user should not have to necessarily repeat the extensive protocol testing of the manufacturer that was used to establish the performance claims. The goals of the method verification study are not to establish analytic performance or to determine if the analytic performance is clinically acceptable, but, simply, to confirm or verify the stated established performance claims of the manufacturer. This implies an abbreviated method evaluation with statistical confirmation that analytic performance is acceptable. Analytic parameters that should be verified are imprecision, inaccuracy (bias), and linearity including analytic sensitivity. Reference ranges should be determined if the patient population is unique, or if the reference range of the analyte is relatively new or unstudied. Principles of method evaluation are discussed.     

Proposed goals for analytical precision and accuracy in single-point diagnostic testing. Theoretical basis and comparison with data from College of American Pathologists proficiency surveys

Expressing total analytic variance as the sum of the squares of imprecision and inaccuracy, or bias, and applying the Cotlove rule recommended by the 1976 College of American Pathologists Conference on Analytical Goals in Clinical Chemistry, namely, that analytic variance should be less than one fourth of the appropriate biological variance, I derive a rule for maximum allowable imprecision in the context of single-point diagnostic testing that takes into account the bias of the test procedure. This rule may be expressed in terms of a population-based reference range (in particular, the range of test results shown in a group of healthy individuals) and the bias of the test method. The latter is required not to exceed one eighth (0.125) of the reference range. These concepts are applied to eight common analytes for which estimates of the biases of specific methods and of within-laboratory imprecision have been published for large numbers of laboratories participating in recent College of American Pathologists proficiency surveys. Results indicate that some methods widely used in 1978 fail to meet the minimum accuracy criterion, while others show negligible bias. Even neglecting bias, more recent data show that average within-laboratory imprecision is still too high for sodium, chloride, and calcium but acceptable for potassium, glucose, cholesterol, urea, and uric acid.     

Quality assurance of analytical methods to guarantee the reliability of medical decision levels for interpretation of clinical laboratory data

We sought to investigate the effects of measurement errors on the evaluation of biological variations in healthy subjects. To this end, we analyzed the allowable limits of analytical error which can guarantee the reliability of medical decision levels for interpretation of clinical laboratory data. As a conclusion, we suggest that one-half or less of biological intra-individual variations is appropriate as the criterion for an allowable limit of error to be applied in health check-ups, and this value is in agreement with those in previous reports. If this criteria as the marker for intra-laboratory imprecision is met, a given institute should be able to evaluate time series change follow up of individual data. If the reference interval of laboratory data for disease screening is shared by different institutes, the criterion of 1/4 or less of a biological inter pulse intra-individual variation should be appropriate. This criterion appears to be the goal to be achieved for analytical inter-laboratory variations. On the other hand, as for the criterion for measurement errors which guarantees disease identification based on the cut-off value, a criterion of 1/4 or less of biological inter-pulse intra-individual variation appears to be appropriate, taking into consideration measurement errors which did not influence false-positive or false-negative rates of disease identification. The value turned out to be the same as the limit for the screening of disease. In this study, we considered allowable limits of error in the vicinity of reference value concentrations. However, it will be necessary to set separately the criteria for data in abnormal ranges.     

Domestic and international trends concerning allowable limits of error in external quality assessment scheme

Many external quality assessment schemes (EQAS) are performed to support quality improvement of the services provided by participating laboratories for the benefits of patients. The EQAS organizer shall be responsible for ensuring that the method of evaluation is appropriate for maintenance of the credibility of the schemes. Procedures to evaluate each participating laboratory are gradually being standardized. In most cases of EQAS, the peer group mean is used as a target of accuracy, and the peer group standard deviation is used as a criterion for inter-laboratory variation. On the other hand, Fraser CG, et al. proposed desirable quality specifications for any imprecision and inaccuracies, which were derived from inter- and intra-biologic variations. We also proposed allowable limits of analytical error, being less than one-half of the average intra-individual variation for evaluation of imprecision, and less than one-quarter of the inter- plus intra-individual variation for evaluation of inaccuracy. When expressed in coefficient of variation terms, these allowable limits may be applied at a wide range of levels of quantity.     

Evaluation of the clinical accuracy of laboratory tests

Fundamental clinical performance of a laboratory test can be described in terms of accuracy, or the ability to correctly classify subjects into clinically relevant subgroups. Accuracy refers to the quality of the information provided by the classification device and should be distinguished from the efficacy, or practical usefulness, of the information. Receiver operating characteristic curves provide a pure index of accuracy by demonstrating the limits of a test's ability to discriminate between alternative states of health over the complete spectrum of operating conditions. If analytical imprecision is removed from the data, the resulting receiver operating characteristic curve represents the inherent biological variation that ultimately limits the clinical accuracy of the test.     

Allowable limits of analytical error which can guarantee the reliability of reference intervals for interpretation of clinical laboratory data

The International Organization for Standardization (ISO) developed a guide to the expression of uncertainty in measurement (GUM). The purpose of such guidance is to provide a basis for the international comparison of measurement results. In this study, we propose a basic protocol to evaluate and express uncertainty in measurement for routine test results in the clinical laboratory. We also sought to investigate the effects of measurement errors on the evaluation of biological variations in healthy subjects. To this end, we analyzed the allowable limits of analytical error which guarantee the reliability of reference intervals for the interpretation of clinical laboratory data. As a conclusion, we suggest that 1/2 or less of biological intraindividual variations is an appropriate criterion for an allowable limit of uncertainty to be applied in health check-ups, and this value is in agreement with previous reports. If this criterion as a marker for intra laboratory imprecision is met, it suggests that a given institute is able to evaluate time series changes in follow-up of individual data. If the reference interval of laboratory data for disease screening is shared by different institutes, it is suggested that a criterion of 1/4 or less of a biological inter- pulse intra-individual variation is appropriate. This criterion appears to be the goal for analytical inter-laboratory variations.     

International standards for tuberculosis care: relevance and implications for laboratory professionals

On World Tuberculosis (TB) Day 2006, the International Standards for Tuberculosis Care (ISTC) was officially released and widely endorsed by several agencies and organizations. The ISTC release was the culmination of a year long global effort to develop and set internationally acceptable, evidence-based standards for tuberculosis care. The ISTC describes a widely endorsed level of care that all practitioners, public and private, should seek to achieve in managing individuals who have or are suspected of having, TB and is intended to facilitate the effective engagement of all healthcare providers in delivering high quality care for patients of all ages, including those with smear-positive, smear-negative and extra-pulmonary TB, TB caused by drug-resistant Mycobacterium tuberculosis and TB/HIV coinfection. In this article, we present the ISTC, with a special focus on the diagnostic standards and describe their implications and relevance for laboratory professionals in India and worldwide. Laboratory professionals play a critical role in ensuring that all the standards are actually met by providing high quality laboratory services for smear microscopy, culture and drug susceptibility testing and other services such as testing for HIV infection. In fact, if the ISTC is widely followed, it can be expected that there will be a greater need and demand for quality assured laboratory services and this will have obvious implications for all laboratories in terms of work load, requirement for resources and trained personnel and organization of quality assurance systems.     

生物学变异的质量规范在全自动干式生化分析仪中的应用

目的 探讨生物学变异的质量规范在全自动干式生化分析仪中的应用.方法 收集2016年VITR0350全自动干式生化分析仪11个检测项目的室内质量控制的不精密度和全年室间质量评价的偏倚,并根据TE=l.96s+| Bias |计算出各项目总误差,然后分别与生物学变异推导出的质量规范的3个层次要求进行比较和分析,并计算出相应的σ值和QGI值,从而评估干式生化分析仪的检测性能,进而进行质量改进.结果 按照生物学变异的最佳、适当和最低的3个层次的质量规范要求,仪器11个检测项目的不精密度、偏倚和总误差的符合率分别为60％/36.4％/81.8％;90.9％/81.8％/90.9％:100％/100％/100％;按照3个层次要求σ值的优秀以上和良好以上符合率分别为18.2％/36.4％;63.6％/81.8％;90.9％/90.9％,而刨除ALB外,按照3个层次要求,σ值的良好以上符合率则为36.4％/90％/100％.BUN、TBIL、AST、CK、URIC不需要改进质量,其他检测项目的QGI均＜0.8,都需要改进精密度.结论 除了ALB依然按照CLIA'88质量规范要求外,其它10个检测项目均可以按照生物学变异的适当层次的质量规范要求,是更高标准的质量要求,VITR0350全自动干式生化分析仪非常适合临床应用.     

终点法测定缺血修饰白蛋白(IMA)的评价及其应用研究

目的对终点法测定缺血修饰白蛋白(IMA)试剂盒进行性能评价,判断其分析性能是否满足临床要求。方法应用终点法测定血清中的IMA含量,对试剂盒的线性、精密度和准确度做出评价。结果质控品的日内CV分别为:低值血清CV=2.12%,高值血清CV=0.48%;日间CV分别为:低值血清CV=2.46%,高值血清CV=2.73%。连续10次测定2个水平的定值质控,得到低值和高值质控的准确率分别为99.95%和99.98%。回收率为99.50%～105.70%。线性试验表明IMA(R2=0.9999)有很好的线性范围。干扰试验表明,溶血、乳糜和黄疸等干扰因素对于IMA测定影响不大。危重病组和急性冠脉综合征(ACS)组的IMA显著低于健康对照组(P0.01)。结论该商品化缺血修饰白蛋白(IMA)试剂盒符合实验室性能标准,且灵敏、方便、简单,可批量测定,适用于临床检验。IMA的特异性较好,对于ACS的诊断具有重要意义。     

Ways of assessing quality goals for diagnostic tests in clinical situations

Although clinical reasoning may be very complex, it is possible to evaluate the effects of analytical variability and error for an analyte in situations in which clinical decisions are mainly based on the results of quantitative measurements of the specific analytical component. The consequences, or the validating of these consequences, can then define the quality goals for the component in the clinical situation. Two situations are investigated: a bimodal situation, ie, a situation in which the component is used for classifying patients into diagnostic groups and the diagnosis can be confirmed; and a unimodal situation, in which the risk of later development of a certain disease increases with the concentration of the component. The bimodal situation is illustrated by the application of creatine kinase isoenzyme measurements in the early diagnosis of acute myocardial infarction and by measurement of blood thyroid-stimulating hormone in screening for congenital hypothyroidism. The unimodal situation is evaluated by serum cholesterol measurement results for identifying individuals at risk regarding ischemic coronary heart disease. It is shown that this system is extremely sensitive to the effects of analytical bias and imprecision. The evaluation of clinical consequences as caused by analytical bias and imprecision makes it possible to define goals for stable analytical performance and for the maximal tolerable unstable performance when the clinical application of the test is well known.     

Influence of analytical and biological variation on the clinical interpretation of seminal parameters

Quality assurance in semen analysis has been questioned recently in this journal. Based on the limited capacity of seminal parameter in the determination of fertility, the authors advocated abandoning methods of quality assurance in semen analysis for clinical situations. In this article, we explore arguments as to why quality assurance in semen analysis for clinical use is not 'a waste of time'. Imprecision and within-subject biological variations are the two major components involved in the dispersion of seminal parameter results obtained by analysis of a semen sample from an individual. As within-subject biological variation is constant across geography, time and population, imprecision is a very important factor in the quality of laboratory test results. We analyse this influence on various seminal parameters and observe that there is an amount of error that can be tolerated without invalidating the medical usefulness of seminal parameter determination. However, there is a maximum allowable analytical error above which the medical usefulness of seminal parameter results is invalidated. The level of performance required to facilitate clinical decision-making is termed quality specification. We comment on different strategies to define the maximum allowable analytical error.     

Flow cytometric enumeration of micronucleated reticulocytes: high transferability among 14 laboratories

This laboratory previously described a single-laser flow cytometric method, which effectively resolves micronucleated erythrocyte populations in rodent peripheral blood samples. Even so, the rarity and variable size of micronuclei make it difficult to configure instrument settings consistently and define analysis regions rationally to enumerate the cell populations of interest. Murine erythrocytes from animals infected with the malaria parasite Plasmodium berghei contain a high prevalence of erythrocytes with a uniform DNA content. This biological model for micronucleated erythrocytes offers a means by which the micronucleus analysis regions can be rationally defined, and a means for controlling interexperimental variation. The experiments described herein were performed to extend these studies by testing whether malaria-infected erythrocytes could also be used to enhance the transferability of the method, as well as control intra- and interlaboratory variation. For these studies, blood samples from mice infected with malaria, or treated with vehicle or the clastogen methyl methanesulfonate, were fixed and shipped to collaborating laboratories for analysis. After configuring instrumentation parameters and guiding the position of analysis regions with the malaria-infected blood samples, micronucleated reticulocyte frequencies were measured (20,000 reticulocytes per sample). To evaluate both intra- and interlaboratory variation, five replicates were analyzed per day, and these analyses were repeated on up to five separate days. The data of 14 laboratories presented herein indicate that transferability of this flow cytometric technique is high when instrumentation is guided by the biological standard Plasmodium berghei.     

Quality improvement in the laboratory assessment of in vitro fertilization.

There has been a trend to use fewer laboratory tests during ovarian hyperstimulation prior to oocyte recovery, in vitro fertilization, and embryo transfer. Estradiol is routinely monitored during ovulation induction protocols. Estradiol rises steadily to supraphysiologic concentration during ovarian hyperstimulation. Review of the College of American Pathologists proficiency testing data from 1990 reveal that the within-method interlaboratory coefficient of variation meets the proposed maximum allowable analytical error of 11.8%. The luteinizing hormone level increases during ovarian hyperstimulation with a skewed distribution. Molecular variants exist that may bind with different affinities to monoclonal antibodies used in two-site sandwich assays. Polyclonal radioimmunoassays usually overestimate luteinizing hormone concentration. The College of American Pathologists proficiency testing data reveal that only three of eight methods with greater than 20 participants had a within-method interlaboratory coefficient of variation that met the proposed maximum allowable analytical error of 10% or less. International standardization of reference standards, antibodies, and labeling methods may improve the performance of this assay. The low pregnancy rate experienced by in vitro fertilization protocols suggests that additional laboratory tests need to be developed to monitor the receptivity of the endometrium for implantation and the quality of the oocyte and embryo.     

The experience of 3 years of external quality assessment of preimplantation genetic diagnosis for cystic fibrosis

Preimplantation genetic diagnosis (PGD) was first performed over 20 years ago and has become an accepted part of genetic testing and assisted reproduction worldwide. The techniques and protocols necessary to carry out genetic testing at the single-cell level can be difficult to master and have been developed independently by the laboratories worldwide offering preimplantation testing. These factors indicated the need for an external quality assessment (EQA) scheme for monogenic disease PGD. Toward this end, the European Society for Human Reproduction and Embryology came together with United Kingdom National External Quality Assessment Services for Molecular Genetics, to create a pilot EQA scheme followed by practical EQA schemes for all interested parties. Here, we detail the development of the pilot scheme as well as development and findings from the practical (clinical) schemes that have followed. Results were generally acceptable and there was marked improvement in results and laboratory scores for those labs that participated in multiple schemes. Data from the first three schemes indicate that the EQA scheme is working as planned and has helped laboratories improve their techniques and result reporting. The EQA scheme for monogenic PGD will continue to be developed to offer assessment for other monogenic disorders.     

The Role of Microbiologists and the Clinical Laboratory in Identifying Infections in Survivors of Pediatric Sexual Abuse: a Difficult Task and an Ethical Responsibility

There are few standards for the clinical examination methods used in suspected cases of sexual abuse; therefore, there is debate about which laboratory test methods should be used. The lack of standards for sample collection from and testing of children creates additional challenges, in part because of the differences in biology and pathogen interaction with children's cells and in part because of the additional emotional impact of a pediatric case. The incidence of child sexual abuse (CSA) is much higher than the general population or health care professionals realize. Potential CSA victims have been traumatized by the experience; therefore, the physical examination that follows needs to be performed in a “safe” environment. The laboratory may get requests to evaluate samples collected from potential perpetrators, as well. The normal pre-analytical, analytical, and post-analytical procedures used are inadequate when used to evaluate specimens collected from survivors of abuse. Specific procedures and policies need to be instituted to aid in the diagnosis of a sexually transmissible disease (STD), indicative of sexual contact. Coordinating the examination of potential victims requires using a multidisciplinary team to ensure proper collection, delivery, and processing of samples, and the identification of organisms known to cause an STD is a difficult task. In addition, the results of testing and potential confirmation of positive results are important aspects of care. The original sample must be retained so that additional testing may be performed, if indicated. Since many potential perpetrators admit to the crime following positive STD organism identification, the microbiology laboratory must work with clinicians, nursing, law enforcement, administrators, and the legal department of the health care system to offer testing for STDs. Approved interdisciplinary policies should be stringently followed, and the laboratory must be ready to be cross-examined during the litigation process. Practical suggestions for those performing testing for CSA are detailed in this review.     

An evaluation of analytic goals for assays of drugs: a College of American Pathologists Therapeutic Drug Monitoring Survey Study

OBJECTIVE: To determine if the levels of imprecision of the commonly used analytic methods for drug measurements are suitable for long-term therapeutic drug monitoring. DESIGN: In 1996, 4 identical lyophilized samples (2 in the first mailing and 2 in the second mailing 4 months later) were sent to laboratories participating in a nationwide proficiency testing program. Similarly, in 1999, replicates from a liquid pool of spiked sera were mailed 3 times, 4 months apart, to participating laboratories. For each of 11 drugs regulated under the Clinical Laboratory Improvement Amendments of 1988 and 1 metabolite, the total variance for each method was partitioned into within- and between-laboratory components. The total within-laboratory and the total survey coefficients of variation (CVs) for each method were then compared with the "acceptable" precision criteria of Glick, Burnett, and Fraser for each drug. SETTING: The first 2 mailings of the College of American Pathologists Therapeutic Drug Monitoring surveys for 1996, sets Z and ZM, and the 3 mailings of 1999, sets ZM, Z, and Z2. MAIN OUTCOME MEASURES: For each drug studied, the CV of each method was compared with the various imprecision criteria, and if greater than any of the criteria, the method was then tabulated as not meeting that specific criterion.Participants.-The approximately 5000 participants of the survey. RESULTS: The number of methods deemed as not having acceptable total long-term within-laboratory precision by the various criteria ranged from 35% to 88% in 1996 and from 22% to 77% in 1999. CONCLUSION: The number of failures possibly indicates that many of the reagent assays being utilized are not precise enough for long-term therapeutic drug monitoring of chronically administered drugs or that the published criteria used to evaluate the data in this study are too stringent.     

Clinically useful limits (CUL) criteria as a basis for quality control including minimal and optimal goals for quality control

Quality control goals for quantitative clinical chemistry assays are reviewed. Recommendations for clinically useful limits (CUL) criteria as minimally acceptable +/- 2 SD for run-to-run and/or day-to-day technical reliability are presented in terms of biologic variations for different levels and clinical applications. A review of the literature and the questionnaire response of a medical school staff presented in this study reveal striking agreement of acceptable analytic goals based on physicians' opinions, biologic variation, and practical analytic feasibility. The current state-of-the-art in clinical laboratories can approach excellence because actual within-laboratory 2-SD variability estimates are somewhere between acceptable CUL criteria and twice as good. Assessing the reliability of laboratory reports based on accuracy and precision or total analytic error is also discussed.