Comparison of fresh frozen serum to traditional proficiency testing material in a College of American Pathologists survey for ferritin, folate, and vitamin B12

Integrating quality control and external quality assurance

Effective management of clinical laboratories relies upon an understanding of Quality Control and External Quality Assurance principles. These processes, when applied effectively, reduce patient risk and drive quality improvement. In this Review, we will describe the purpose of QC and EQA and their role in identifying analytical and process error. The two concepts are linked, and we will illustrate that linkage. Some EQA providers offer far more than analytical surveillance. They facilitate training and education and extend quality improvement and identify areas where there is potential for patient harm into the pre-and post-analytical phases of the total testing process.

Biomarkers of Nutrition for Development (BOND)-Iron Review

This is the fifth in the series of reviews developed as part of the Biomarkers of Nutrition for Development (BOND) program. The BOND Iron Expert Panel (I-EP) reviewed the extant knowledge regarding iron biology, public health implications, and the relative usefulness of currently available biomarkers of iron status from deficiency to overload. Approaches to assessing intake, including bioavailability, are also covered. The report also covers technical and laboratory considerations for the use of available biomarkers of iron status, and concludes with a description of research priorities along with a brief discussion of new biomarkers with potential for use across the spectrum of activities related to the study of iron in human health.The I-EP concluded that current iron biomarkers are reliable for accurately assessing many aspects of iron nutrition. However, a clear distinction is made between the relative strengths of biomarkers to assess hematological consequences of iron deficiency versus other putative functional outcomes, particularly the relationship between maternal and fetal iron status during pregnancy, birth outcomes, and infant cognitive, motor and emotional development. The I-EP also highlighted the importance of considering the confounding effects of inflammation and infection on the interpretation of iron biomarker results, as well as the impact of life stage. Finally, alternative approaches to the evaluation of the risk for nutritional iron overload at the population level are presented, because the currently designated upper limits for the biomarker generally employed (serum ferritin) may not differentiate between true iron overload and the effects of subclinical inflammation.

Commutability and traceability in EQA programs

OBJECTIVES

The concept of commutability of samples has focused laboratories on the importance of traceability. However, the critical role of External Quality Assurance (EQA) in achieving the primary role of traceability (i.e. facilitating comparable patient results in different laboratories) has largely been lost. The aim of this paper is to review the role of EQA in achieving traceable/commutable results.

DESIGN AND METHODS

The role of commutability and traceability in EQA and Internal Quality Control (IQC) are discussed. Examples of commutable EQA samples are given to highlight the problem of assuming EQA material does not behave like patient samples.

RESULTS

We provide the conventional traceability chain (top down) and the role of EQA in a "bottom up" model using conventional EQA samples.

CONCLUSIONS

The quest for commutable samples has compromised the value of EQA without an understanding that some EQA materials are commutable for some measurands. EQA plays a key role in performance improvement, but laboratories need to understand the importance of using a range of values appropriate to the assay to identify areas of quality need. Traceability and EQA using conventional samples are not mutually exclusive concepts.

Framework for laboratory harmonization of folate measurements in low- and middle-income countries and regions

The measurement of serum and red blood cell folate, two commonly used biomarkers of folate status in populations, is complicated by analytical and data interpretation challenges. Folate results show poor comparability across laboratories, even using the same analytical technique. The folate microbiologic assay produces accurate results and requires simple instrumentation. Thus, it could be set up and maintained in low- and middle-income country laboratories. However, the assay has to be harmonized through the use of common critical reagents (e.g., microorganism and folate calibrator) in order to produce comparable results across laboratories and over time, so that the same cutoff values can be applied across surveys. There is a limited need for blood folate measurements in a country owing to the periodic nature of surveys. Having a network of regional resource laboratories proficient in conducting the folate microbiologic assay and willing and able to perform service work for other countries will be the most efficient way to create an infrastructure wherein qualified laboratories produce reliable blood folate data. Continuous participation of these laboratories in a certification program can verify and document their proficiency. If the resource laboratories conduct the work on a fee-for-service basis, they could become self-sustaining in the long run.

Biomarkers of Nutrition for Development-Folate Review

The Biomarkers of Nutrition for Development (BOND) project is designed to provide evidence-based advice to anyone with an interest in the role of nutrition in health. Specifically, the BOND program provides state-of-the-art information and service with regard to selection, use, and interpretation of biomarkers of nutrient exposure, status, function, and effect. To accomplish this objective, expert panels are recruited to evaluate the literature and to draft comprehensive reports on the current state of the art with regard to specific nutrient biology and available biomarkers for assessing nutrients in body tissues at the individual and population level. Phase I of the BOND project includes the evaluation of biomarkers for 6 nutrients: iodine, iron, zinc, folate, vitamin A, and vitamin B-12. This review represents the second in the series of reviews and covers all relevant aspects of folate biology and biomarkers. The article is organized to provide the reader with a full appreciation of folate's history as a public health issue, its biology, and an overview of available biomarkers (serum folate, RBC folate, and plasma homocysteine concentrations) and their interpretation across a range of clinical and population-based uses. The article also includes a list of priority research needs for advancing the area of folate biomarkers related to nutritional health status and development.

Statistical validation of reagent lot change in the clinical chemistry laboratory can confer insights on good clinical laboratory practice

Verification of new lot reagent's suitability is necessary to ensure that results for patients' samples are consistent before and after reagent lot changes. A typical procedure is to measure results of some patients' samples along with quality control (QC) materials. In this study, the results of patients' samples and QC materials in reagent lot changes were analysed. In addition, the opinion regarding QC target range adjustment along with reagent lot changes was proposed. Patients' sample and QC material results of 360 reagent lot change events involving 61 analytes and eight instrument platforms were analysed. The between-lot differences for the patients' samples (ΔP) and the QC materials (ΔQC) were tested by Mann-Whitney U tests. The size of the between-lot differences in the QC data was calculated as multiples of standard deviation (SD). The ΔP and ΔQC values only differed significantly in 7.8% of the reagent lot change events. This frequency was not affected by the assay principle or the QC material source. One SD was proposed for the cutoff for maintaining pre-existing target range after reagent lot change. While non-commutable QC material results were infrequent in the present study, our data confirmed that QC materials have limited usefulness when assessing new reagent lots. Also a 1 SD standard for establishing a new QC target range after reagent lot change event was proposed.

Proficiency testing/external quality assessment: current challenges and future directions

BACKGROUND

Proficiency testing (PT), or external quality assessment (EQA), is intended to verify on a recurring basis that laboratory results conform to expectations for the quality required for patient care.

CONTENT

Key factors for interpreting PT/EQA results are knowledge of the commutability of the samples used and the process used for target value assignment. A commutable PT/EQA sample demonstrates the same numeric relationship between different measurement procedures as that expected for patients' samples. Noncommutable PT/EQA samples frequently have a matrix-related bias of unknown magnitude that limits interpretation of results. PT/EQA results for commutable samples can be used to assess accuracy against a reference measurement procedure or a designated comparison method. In addition, the agreement of the results between different measurement procedures for commutable samples reflects that which would be seen for patients' samples. PT/EQA results for noncommutable samples must be compared to a peer group mean/median of results from participants who use measurement procedures that are expected to have the same or very similar matrix-related bias. Peer group evaluation is used to asses whether a laboratory is using a measurement procedure in conformance to the manufacturer's specifications and/or in conformance to other laboratories using the same technology. A noncommutable PT/EQA sample does not give meaningful information about the relationship of results for patients' samples between different measurement procedures.

SUMMARY

PT/EQA provides substantial value to the practice of laboratory medicine by assessing the performance of individual laboratories and, when commutable samples are used, the status of standardization or harmonization among different measurement procedures.

Advances in standardization of laboratory measurement procedures: implications for measuring biomarkers of folate and vitamin B-12 status in NHANES

Population studies such as NHANES analyze large numbers of laboratory measurements and are often performed in different laboratories using different measurement procedures and over an extended period of time. Correct clinical and epidemiologic interpretations of the results depend on the accuracy of those measurements. Unfortunately, considerable variability has been observed among assays for folate, vitamin B-12, and related biomarkers. In the past few decades, the science of metrology has advanced considerably, with the development of improved primary reference measurement procedures and high-level reference materials, which can serve as the basis for accurate measurement. A rigorous approach has been established for making field methods traceable to the highest-level reference measurement procedures and reference materials. This article reviews some basic principles of metrology and describes their recent application to measurements of folate and vitamin B-12.

Commutability Limitations Influence Quality Control Results with Different Reagent Lots

BACKGROUND

Good laboratory practice includes verifying that each new lot of reagents is suitable for use before it is put into service. Noncommutability of quality control (QC) samples with clinical patient samples may preclude their use to verify consistency of results for patient samples between different reagent lots.

METHODS

Patient sample results and QC data were obtained from reagent lot change verification records for 18 QC materials, 661 reagent lot changes, 1483 reagent lot change–QC events, 82 analytes, and 7 instrument platforms. The significance of between-lot differences in the results for QC samples compared with those for patient samples was assessed by a modified 2-sample t test adjusted for heterogeneity of QC and patient sample measurement variances.

RESULTS

Overall, 40.9% of reagent lot change–QC events had a significant difference (P < 0.05) between results for QC samples compared with results for patient samples between 2 reagent lots. For QC results with differences <1.0 SD interval (83.1% of total), 37.7% were significantly different from the changes observed for patient samples. For QC results with differences ≥1.0 SD interval (16.9% of total), 57.0% were significantly different from those for patient samples.

CONCLUSIONS

Occurrence of noncommutable results for QC materials was frequent enough that the QC results could not be used to verify consistency of results for patient samples when changing lots of reagents.

Ordering folate assays is no longer justified for investigation of anemias, in folic acid fortified countries

Background

Since 1998, in the countries where there is mandatory fortification of grain products with folic acid, folate deficiency has become very rare. Consequently, we decided to find out whether there is any justification for ordering folate assays for investigation of anemias.

Methods

We reviewed serum folate (SF) and red cell folate (RF) data at two teaching hospitals in Canada. At the Health Sciences Centre (HSC) the folate data for the year 2001 were analyzed and the medical records of those with low SF or low RF were reviewed. At St. Boniface General Hospital(SBGH)all folate data between January 1996 and Dec 31,2004 were analyzed and the medical records of all who had low RF between January 1,1999 and December 31,2004 were reviewed.

Results

In 2001, at HSC, 11 out of 2154(0.5%)SF were low(<7.0 nmol/L) and 4 out of 560 (0.7%) RF were low (<417 nmol/L). In no subject with low SF or RF could the anemia be attributed to folate deficiency. At SBGH during the 3-year-period of 1999-2001, 19 out of 991(1.9%) had low RF (<225 nmol/L) but in only 2 patients (0.2%) the low RF was in folate deficiency anemia range; but neither of them had anemia.

Conclusion

In countries where there is mandatory fortification of grain products with folic acid, folate deficiency to the degree that could cause anemia is extremely rare. Ordering folate assays for investigation of anemias, in these countries, is waste of time and money. The result of these tests is more likely to mislead the physicians than to provide any useful information.

Variations observed for insulin concentrations in an interlaboratory quality control program may be due to interferences between reagents and the matrix of the control materials

The present study was carried out to observe the behaviour of insulin concentrations in an interlaboratory quality control program from BioRad Laboratories (Irving, CA) applied to Immulite 2000 (Diagnostics Product Corporation, Los Angeles, CA) for three control materials of Lyphocheck Immunoassay Plus Control. Insulin was measured for 261 consecutive working days in a year using a solid-phase immunometric chemiluminescent assay; likewise insulin was measured for 55 days during a period of 4 months in a pool of sera obtained from patients with insulin concentrations within the normal range of our laboratory. The results from each control material were classified in three groups according to the closeness among concentrations and time; mean concentrations were significantly different between consecutive groups for the three control materials (p<0.0001). However, no differences were observed in samples from pool sera. The variations observed in insulin concentrations of the control materials may be due to some interferences or matrix effect on the control material caused by the reagents to quantify insulin in the Immulite 2000.

Total Long-term Within-Laboratory Precision of Cortisol, Ferritin, Thyroxine, Free Thyroxine, and Thyroid-Stimulating Hormone Assays Based on a College of American Pathologists Fresh Frozen Serum Study: Do Available Methods Meet Medical Needs for Precision?

Context.—It is important that the total long-term precision of laboratory methods meet the medical needs of the patients being served.

Objectives.—To determine the long-term within- and between-laboratory variation of cortisol, ferritin, thyroxine, free thyroxine, and thyroid-stimulating hormone measurements using commonly available methods and to determine if these variations are within accepted medical needs.

Design.—Two vials of pooled frozen serum were mailed 6 months apart to laboratories participating in 2 separate College of American Pathologists surveys. The data from those laboratories that analyzed an analyte in both surveys were used to determine for each method the total variance and the within- and between-laboratory components.

Setting.—The study included the A mailing of the 2003 College of American Pathologists Ligand Survey and the C mailing of the Chemistry Survey.

Main Outcome Measures.—For each analyte, total variance was partitioned into within- and between-laboratory components for each analytic method. The within-laboratory variations were then compared with imprecision criteria based on biological variation.

Participants.—The laboratories that reported results on the same analyte using the same method in both surveys.

Results.—For each analyte, the median of the long-term within-laboratory variances of each peer group was 78% to 95% of its total-survey variance, and the median long-term within-laboratory coefficients of variation varied from 5.1% to 7.6%. The number of methods that met within-laboratory imprecision goals based on biological criteria were 5 of 5 for cortisol; 5 of 7 for ferritin; 0 of 7 for thyroxine and free thyroxine; and 8 of 8 for thyroid-stimulating hormone.

Conclusions.—For all analytes tested, the total within-laboratory component of variance was the major source of variability in this study. In addition, there are several methods, especially for thyroxine and free thyroxine, that may not meet analytic goals in terms of their imprecision.