Intralaboratory Quality Control Research Articles

Development, certification, and use of a pharmacopoeial standard for the content of immunoglobulin A in human immunoglobulins for parenteral administration

Scientific relevance. The immunoglobulin A (IgA) impurity content in parenteral human immunoglobulins should be determined in accordance with the State Pharmacopoeia of the Russian Federation by kinetic nephelometry, radial immunodiffusion, or enzyme immunoassay (ELISA) with a reference standard. The International Standard (IS) for the content of IgA is certified using gravimetry and radial immunodiffusion. However, neither of the existing standards for the content of IgA in human immunoglobulins is currently certified using all three compendial methods. This prevents analysts from comparing test results obtained by different methods and may lead to an underestimation of the IgA content in human immunoglobulins.Aim. This study aimed to determine the procedure for the development, certification, and use of a pharmacopoeial reference standard (RS) for the content of IgA in human immunoglobulins.Materials and methods. The authors studied candidate RSs for the IgA content derived from human plasma for fractionation. The IgA content determination involved kinetic nephelometry, radial immunodiffusion, and ELISA, as well as commercial test kits and the IS. The authors quantified the IgA impurity in samples of commercial human immunoglobulins from various manufacturers. The data analysis involved descriptive statistics and variance analysis using Microsoft Excel and Statistica 10.Results. The authors established a pharmacopoeial standard with a certified IgA content of 1.98 mg/mL (expanded uncertainty, 0.44 mg/mL; coverage coefficient, k=2; confidence level, 95%) for IgA impurity quantification in human immunoglobulins by radial immunodiffusion and ELISA and that of 1.31–2.64 mg/mL (expanded uncertainty, 0.67 mg/mL; coverage ratio, k=3; confidence level, 99%) for intralaboratory quality control of IgA impurity quantification by kinetic nephelometry, radial immunodiffusion, and ELISA.Conclusions. The pharmacopoeial standard developed in the study has been included in the register of standards of the State Pharmacopoeia of the Russian Federation as the Reference Standard for the Content of Immunoglobulin Class A (IgA) (Registry No. 3.1.00454). The pharmacopoeial standard is intended for the standardisation of analytical methods for the-determination of the IgA impurity content in parenteral human immunoglobulins.

Graphite Furnace Atomic Absorption Spectrometry for Biomonitoring of Blood Lead Level in Quality Control Blood Materials

Background & Objective: Lead (Pb) is a major toxicant that has threatened human health for years. There is no safe level of exposure and deposition of a small amount of Pb in the human body has a negative impact on an individual's health. Despite recent reductions in its use, it has caused extensive environmental contamination as well. In the present study,the intralaboratory quality control assessment is reported as an initial step in lead determination by Graphite furnace atomic absorption spectrometry (GFAAS).
 Materials & Methods: Varian SpectrAA-220 with partition tube and deuterium background correction was used for the analysis. The evaluation quality control blood material was Seronorm trace elements whole blood (levels I &II).
 Results: The lowest method limit of detection was 0.74 μg/dL, and based on the regression analysis, the lowest quantification concentration was 3.00 μg/dL (CV = 4.6 %). In addition, obtained %CV for Seronorm (I) & Seronorm (II) was 7.3% & 5.4% respectively.
 Conclusion: In recent years, several diverse technological advancements in blood lead level determination have occurred. At the same time, demands for blood lead (BPb) level determination by GFAAS has been increased by public health in order to identify children exposed to lead in the environment, and by occupational health to reduce excessive exposure in the lead industries. The obtained results indicated that for BPb analysis, the method described by GFAAS is still a reference routine analytical technique that requires less time and no matrix matched standard curve, allowing blood samples to be run against aqueous calibration standards which eliminates the need for standard additions.

Molecular Diagnostics of Oncological Disease: Prospects for the Development of a Reference Material for the HER2 gene Content

Cancer is the leading cause of death in the world. The development of oncopathology is closely related to various changes in the genetic material that occur in malignantly transformed cells. Medical decision-making requires a clear differentiation between normal and pathological indicators, which are, among other things, the results of application of quantitative methods in laboratory medicine. Studies of DNA isolated from a patient’s biological material, identification and measurement of the content of nucleotide sequences acting as oncopathology biomarkers allow to solve the problems of determining the genetic prerequisites for cancer, its early diagnosis, determining the treatment strategy, monitoring, and confirming the patient’s cure.The purpose of this research is to develop the main approaches to the design of DNA reference materials (RMs) for metrological support of molecular diagnostics of oncopathology through the example of the RM for the HER2 gene sequence content in the human genome, with the value of «the number of copies of the DNA sequence» which is metrologically traceable to the natural SI unit «one».In the course of the research, a technique for measuring the HER2 gene amplification (the number of copies of the gene sequence per genome) was developed based on the use of the digital PCR method (dPCR). Comparability of measurement results for the method developed by the authors, and the results obtained using a commercial kit by the MLPA method on samples of human biological material is shown.Five permanent cell lines obtained from the CUC «Vertebrate Cell Culture Collection» were characterized in relation to the copy number ratios of HER2 gene sequence and CEP17 and RPPH1 genes sequences. A cell line with the HER2 gene amplification was identified. The results obtained will be used to create the RM for the copy number ratio of the HER2 gene sequences and the RPPH1 and CEP17 gene sequences. Creation of matrix DNA RMs based on human cell cultures certified using dPCR will allow transferring the unit of copy numbers of the DNA sequence to calibrators included in medical devices, thereby ensuring the required reliability and comparability of measurement results in the laboratory diagnostics of oncopathology, as well as the possibility of calibrating routine methods of DNA diagnostics and intralaboratory quality control.

Оптимизация методов внутрилабора-торного контроля качества

The article outlines and analyzes the experience of optimizing intra-laboratory quality control of the analytical stage of research in the clinical and diagnostic laboratory. Emphasized is the advantage of the use of automated electronic cards in comparison with processing indicators manually by reducing time and increasing the accuracy of laboratory data

Microorganism idenitfication – stability and correctness of mass spectrometry method (MALDI TOF MS)

Introduction: MALDI TOF MS method is increasingly used in routine microbiological diagnostics to identify clinical strains. The result of the identification test is based on the measurement of the mass, charge and flight time of the protein ions. This makes it possible to monitor and supervise the method using a numerical score developed with statistical techniques. Aim: The study aimed to determine the stability and correctness of the mass spectrometry method. Materials and methods: To evaluate the characteristics of the method, microbial identification tests were performed using reference strains. All tests were performed as part of the MALDI TOF MS internal quality control system. Results: All reference strains (100%) were correctly identified to the species level, although the score values were not always within the reliability criteria of the results established by the producer. It was found that the mean values of the score were from 2.000 – 2.299 (49.2%) and 2.300 – 3.000 (50.0%). The coefficient of variation for control tests performed in the consecutive years ranged from 5.18 – 6.56%, which evidence of the high stability of the method. For individual species, reproducibility precision over the 8 years ranged from 2.89% (n = 13) for Enterococcus faecalis ATCC 51299 to 7.02% (n = 28) for Klebsiella pneumoniae ATCC 700603, which proves the high precision of measurements. Conclusions: The mass spectrometry method is characterized by very high stability and correctness. The intra-laboratory quality control system using reference strains is a useful tool for monitoring and supervising the method and laboratory personnel competency performing identification tests during routine microbiological work.

Standardization of methods for determining ESR.

The study presents a historical analysis of the problems of standardization of methods for determining ESR. The modern approaches to the automation of ESR research are presented. It is shown that the solution to the problems of standardization of methods for determining ESR lies in the plane of regular intra-laboratory quality control. In accordance with the principles of evidence-based medicine, recommendations are given on the use of methods for determining ESR in clinical practice.

Application of the registration template for in-laboratory quality control data analysis in the MS Excel program in the activities of a medical laboratory technician

The article provides information on the creation and application of a template for registration and analysis of intralaboratory quality control data. The reasons for creating a template are considered; the activities of a medical laboratory technician without using a template and with its application are analyzed. The study confirms that the use of a ready-made template created in a spreadsheet processor greatly facilitates and optimizes the work of a medical laboratory technician.

The use of intralaboratory and external quality control of immunohistochemical studies to improve the detection of estrogen and progesterone receptors

Immunohistochemical study of breast cancer has been practiced for several decades; however, the standardization of this process has not yet been achieved, despite substantial advances in methodology. The paper presents practical guidelines and standards for testing breast carcinomas, which can be used as day-to-day control of the work of an immunohistochemistry laboratory. It considers the concept of external quality control in the immunohistochemical detection of estrogen (ER) and progesterone (PR) receptors, as well as the problems of harmonization in the immunohistochemical analysis of breast carcinomas, by using the nuclear biomarkers, such as ER and PR, as an example. The agreed standard-based external control in determining the optimal result may yield reproducible data for use in clinical practice.

Creation of reference materials of specific electrical conductivity of aviation fuels as a component of ensuring the uniformity of measurements at chemmotology laboratories

Today in Ukraine there are no reference materials of aviation fuels, including very important reference materials of specific conductivity of aviation fuels. This makes impossible to ensure the accredited laboratories activities for testing aviation fuels. The relevance of creating a set of reference materials of specific electrical conductivity of aviation fuels is caused by the need to ensure the uniformity, traceability and reliability of measurements when assessing the suitability of measurement (testing) methods and proficiency testing in testing chemmotology laboratories accredited for compliance with international standard ISO/IEC 17025. It is also caused by the intermediate inspections of measuring equipment and intra-laboratory quality control over the entire range of measurement methods realizations. An important characteristic for the safety of aircraft engines is the specific conductivity of fuels. This characteristic can be quite easily and accurately measured in each unit from the batch of reference materials. A wide range of values of specific conductivity of reference materials can be obtained with the help of specialized additives. In the article the authors analyze the existing regulations and publications on procedures for the manufacture and use of fuel reference materials in general and specific requirements for fuels used in aviation. The issue of manufacturing is considered and the results of experimental researches of homogeneity and stability of reference materials of aviation fuel taking into account the requirements of DSTU-N ISO Guide 35:2018 are given. It is proposed to create a number of aviation fuel reference materials with antistatic additive and different levels of the certified characteristic value at the range from 25 pS/m to 650 pS/m.

The performance evaluation of unassayed biochemistry serum controls

Objective To evaluate the inter-bottle variations, stability in consumption and interchangeability of unassayed biochemistry serum controls. Methods Comparison between unassayed serum controls from a domestic Pretrol® and an international Bio-Rad manufacturer was conducted in department of laboratory, in May 2016, with Roche Cobas 8000, Roche Hitachi 7600 and Siemens 2400 modular analyzer. The inter-bottle variation was determined by monitoring the inter-batch variation of 10 bottles of control samples after eliminating the intra-batch variation from the same bottle. Stability in consumption was determined as the precision after 7 days storage under 2 ℃ to 8 ℃ or 30 days of storage under -20 ℃ since reconstitution. The interchangeability was determined as the precisionbetween the controls from different manufacturers for the same test. Results The inter-bottle imprecision of controls from domestic manufacturer for 13 biochemistry tests (CV concentration 1/CV concentration 2) were potassium (0.26%/0.42%), sodium (0.26%/0.21%), phosphorus (0.00%/0.62%), cholesterol (0.56%/0.54%), total protein (0.52%/0.33%), albumin (0.44%/2.00%), alanine aminotransferase (1.72%/0.57%), γ-glutamylaminotransferase (0.52%/0.62%), aspartate aminotransferase (3.10%/1.09%), lactate dehydrogenase (0.76%/0.91%), alkaline phosphatase (1.13%/0.97%), amylase (0.30%/0.39%) and glucose (0.00%/0.40%). The stability in consumption of the controls from the domestic manufacturer (CV concentration 1/CV concentration 2 under 2 ℃ to 8 ℃storage; CV concentration 1/CV concentration 2 under -20 ℃ storage) were potassium (1.06%/0.36%; 0.74%/0.48%), sodium (0.49%/0.59%; 0.72%/0.65%), phosphorus (0.95%/0.80%; 1.43%/0.84%), cholesterol (1.49%/1.58%; 2.17%/1.80%), total protein (0.84%/0.75%; 1.60%/1.68%), albumin (1.33%/2.28%; 1.94%/2.43%), alanine aminotransferase (1.41%/0.51%; 3.24%/1.60%) γ-glutamylaminotransferase (1.16%/1.16%; 2.85%/2.49%), aspartate aminotransferase (4.37%/2.14%; 2.99%/1.31%), lactate dehydrogenase (2.70%/2.54%; 3.84%/2.97%), alkaline phosphatase (2.63%/1.96%; 2.31%/2.10%), amylase (0.95%/2.19%; 1.58%/1.38%) and glucose (0.60%/0.48%; 1.41%/1.55%). The Inter-bottle variation and stability in consumption of biochemistry test unassayed controls from the domestic manufacturer were compatible for clinical assay according to the CV% specification from the Clinical Biochemistry Test Quality Requirement (WS/T 403-2012). The imprecision of the controls from both the domestic and international manufacturers (CVp concentration 1/CVp concentration2; CVq concentration 1/CVq concentration 2) were potassium (0.52%/0.46%; 2.39%/0.47%), sodium (0.30%/0.17%; 0.81%/0.47%), phosphorus (2.72%/1.11%; 4.57%/2.07%), cholesterol (0.29%/1.38%; 2.94%/1.81%), total protein (0.66%/2.46%; 1.85%/2.54%), alkaline phosphatase (2.67%/4.66%; 3.58%/8.55%), total bilirubin (5.71%/5.09%; 9.55%/7.41%), albumin (1.10%/2.61%; 4.79%/1.93%), alanine aminotransferase (6.42%/1.25%; 5.74%/1.63%), γ-glutamylaminotransferase (2.27%/4.35%; 4.38%/0.74%), aspartate aminotransferase (0.56%/2.84%; 0.91%/2.11%) and lactate dehydrogenase (2.36%/2.47%; 3.10%/1.52%). The interchangeability of serum controls from domestic manufacturer was better than clinical serum samples. Conclusion The unassayed serum biochemistry test controls from domestic manufacturer are suitable for the intra-laboratory quality control and showed a promising compatibility for inter-laboratory quality control usage. Key words: Quality control; Clinical chemistry tests; Diagnostic tests,routine; Clinical laboratory techniques

QUESTIONS OF THE INTERNAL CONTROL QUALITY ASSURANCE OF TEST'S RESULTS IN THE TESTING LABORATORY

The problems regarding arrangement and implementation of the intralaboratory quality control (ILC) of test results in testing laboratories (TL) are reviewed and summarized. The main goals of ILC directly aimed at minimization of the risks of getting unsatisfactory test results are considered along with the choice of the methods and types of control. The process and system approaches to organization and performance of the ILC are proposed with allowance for the risk assessment at the stages of planning, implementation, and monitoring of the ILC, which provide a control of all measurement techniques (MT) used in the laboratory, thus making the control procedure transparent to all the parties concerned. An effective way to describe the ILC starting with the stage of planning is recommended. The proposed "ILC Program" ensures the efficiency and effectiveness of the process to match the goals set for ILC: ensuring of the required accuracy (uncertainty) of current test results for the entire nomenclature of measurement techniques, maintaining the testing processes in a statistically controlled state, and, consequently, ensuring of the confidence of internal and external customers and supervisory organizations to the results of testing and activities of the TL as a whole thus proving the technical competence of the laboratory. We present the results of analysis of all ILC stages using the Shewhart-Deming — PDCA principle with a list of possible risks of obtaining unreliable results. Recommendations on the effective implementation of each stage of the process are given. Listed typical mistakes of ILC implementation can help the readers not only to avoid them, but also consider them as possible risks.

Russia-made Mueller–Hinton agar: compliance with contemporary requirements

At present, a rise of antimicrobial resistance requires that susceptibility of infectious agents to antimicrobial agents could be accurately evaluated as related errors may lead to selecting improper therapeutics provoking spread of drug resistance. Pathogen sensitivity to antimicrobial agents is commonly determined by a disc diffusion method. A quality of nutrient medium used in assays plays a crucial role influencing final results. In Russia, it turned out that regulatory documents such as the nationwide guidelines and clinical recommendations outlining methodology for antimicrobial susceptibility testing underlay availability in domestic market few nutrient media, including Mueller–Hinton Agar, AGV medium etc. exhibiting sometimes unsatisfactory quality. To harmonize such methodology with international requirements, theStateResearchCenterfor Applied Microbiology and Biotechnology has developed a technology and promoted manufacture of Russia-made Mueller–Hinton agar satisfying requirements of EUCAST documents, clinical guidelines, and ISO/TS 16782:2016. The main objective of this study was to compare quality of new agar product with five similar foreign media while examining 11 test strains by disc diffusion method. As a result, some of nutrient media available to the Russian market turned out to be off-standard: not all of them satisfy to the EUCAST requirements and clinical guidelines since diameter distribution for growth inhibition recommended by EUCAST for quality control does not fit into permissible range. Moreover, susceptibility of P. aeruginosa ATCC 27853 to aminoglycosides, fluoroquinolones, Meropenem, as well as S. aureus ATSS 25923 and E. faecalis ATCC 29212 to tigecycline was assessed with certain mistakes. The data obtained by us were analyzed in accordance to the new document ISO/TS 16782:2016 “Clinical laboratory testing — criterion for acceptable lots of dehydrated Mueller–Hinton agar and broth for antimicrobial susceptibility testing”, not approved yet In Russia. To determine potential reason for deviation of data from reference range, we measured concentration of bivalent metals in all nutrient media examined by atomic emission spectrometry with inductively coupled plasma. We determined new patterns affecting reliability of results on microbial antibiotic susceptibility. A need to check intralaboratory quality control of nutrient media was emphasized.

Algorithm of the intralaboratory quality control for hematology analyzers

Algorithm of the intralaboratory quality control for hematology analyzers

Intralaboratory quality control of calibration results

The article is devoted to the issues of intralaboratory control of measurement results in a calibration laboratory. This is highly important in controlling and supporting the relevant calibration capability of the laboratory. Up to now, there are normative documents, which describe methods for controlling internal quality indicators of analytical measurements. After analyzing all possible options of comparing the quality indicators of the measurement results with critical values in the analytical laboratories and adapting them to the measurement features of the calibration laboratory, the methods of determining the critical limits for comparative measurements in the conditions of repeatability and intermediate precision are demonstrated.Measurement uncertainty in calibration consists of uncertainty effects introduced by reference equipment, test equipment, calibration operator, external conditions, calibration and calculation method, measuring instrument (MI), which is to be calibrated. Proceeding from the well-known practice, the calibration capability of the laboratory should be three to five times smaller than the uncertainty of MIs being calibrated by this laboratory. In order to maintain such a level of calibration, it is necessary to perform timely calibrations of the measurement standards and test equipment (to carry out internal testing of test equipment), validate calibration methods, participate in interlaboratory comparisons in order to determine laboratory bias and perform intralaboratory control of the quality indicators of measurement results in calibration.Several methods of intralaboratory control of measurement results in a calibration laboratory are proposed, namely, the evaluation of consistency of the measurement results in calibration in conditions of intermediate precision with variable factors “operator”, “time” and determination of the limits of repeatability.

Method and platform standardization in MRM-based quantitative plasma proteomics

There exists a growing demand in the proteomics community to standardize experimental methods and liquid chromatography-mass spectrometry (LC/MS) platforms in order to enable the acquisition of more precise and accurate quantitative data. This necessity is heightened by the evolving trend of verifying and validating candidate disease biomarkers in complex biofluids, such as blood plasma, through targeted multiple reaction monitoring (MRM)-based approaches with stable isotope-labeled standards (SIS). Considering the lack of performance standards for quantitative plasma proteomics, we previously developed two reference kits to evaluate the MRM with SIS peptide approach using undepleted and non-enriched human plasma. The first kit tests the effectiveness of the LC/MRM-MS platform (kit #1), while the second evaluates the performance of an entire analytical workflow (kit #2). Here, these kits have been refined for practical use and then evaluated through intra- and inter-laboratory testing on 6 common LC/MS platforms. For an identical panel of 22 plasma proteins, similar concentrations were determined, regardless of the kit, instrument platform, and laboratory of analysis. These results demonstrate the value of the kit and reinforce the utility of standardized methods and protocols. The proteomics community needs standardized experimental protocols and quality control methods in order to improve the reproducibility of MS-based quantitative data. This need is heightened by the evolving trend for MRM-based validation of proposed disease biomarkers in complex biofluids such as blood plasma. We have developed two kits to assist in the inter- and intra-laboratory quality control of MRM experiments: the first kit tests the effectiveness of the LC/MRM-MS platform (kit #1), while the second evaluates the performance of an entire analytical workflow (kit #2). In this paper, we report the use of these kits in intra- and inter-laboratory testing on 6 common LC/MS platforms. This article is part of a Special Issue entitled: Standardization and Quality Control in Proteomics.

<b>Intra-laboratory quality control for chicken raw materials</b> - doi: 10.4025/actascitechnol.v35i3.12657

In recent times, food and water laboratories have aimed to improve their processes to meet market demands. In order to contribute to the efficacy and development of these processes, new methods must be sought, among which is intra-laboratory quality control. This research study portrays the use of this method in a food and water laboratory, in order to analyze the intra-laboratory statistical control of chicken raw materials. To that end, the methodology applied was: Exploratory data analysis; Cochran's test, to assess the homogeneity of variances; Dixon's Test, to verify whether the means are part of the same distribution; calculation of repeatability and reproducibility; calculation of the uncertainty of the mean; Snedecor's F method, to compare the variances; and Dixon's test, to compare laboratory variances. The analysis parameter analyzed in the studied raw material was the proficiency of technicians with regard to the accuracy of analyses of total coliform count in the raw materials prior to chilling. The final results showed low data variation around the mean, as well as significant reliability of the obtained results.

Discriminant function using red cell indices to distinguish between HbC and HbE traits.

Values for MCV, MCH, MCHC and red cell distribution width (RDW) derived from subjects with HbC and HbE traits using a Technicon H*1 automated blood count analyser were compared. Significantly higher MCH, MCHC and RDW values were found in those with HbC trait. By use of a simple discriminant function (MCHC2 x RDW/1000), 19/20 subjects with HbC trait gave a value > or = 16.3, and 20/21 subjects with HbE trait gave a value < or = 16.2. The function described may be of value as an adjunct to electrophoresis in intralaboratory quality control.

Reproducibility of HPV DNA Testing by Hybrid Capture 2 in a Screening Setting

Within a large Italian randomized trial on new technologies for cervical cancer screening involving 7 laboratories with different levels of experience, an intralaboratory and interlaboratory quality control program for human papillomavirus (HPV) DNA testing by Hybrid Capture 2 (HC2; Digene, Gaithersburg, MD) was implemented. To monitor the hybridization and detection steps, target samples containing purified, concentration-defined, HPV DNA were introduced in each test run. Only 3 of 1,024 showed a mistake in a positive vs negative classification with a 1 relative light unit (RLU)/positive control specimen (PC) ratio cutoff. To monitor the preanalytic steps (particularly denaturation), blinded specimens (33 collected in PreservCyt (Cytyc, Boxborough, MA) and 36 in Specimen Transport Medium (STM, Digene) were centrally prepared, divided into aliquots, and sent to each laboratory. The multiple-rater scores for negative (<1 RLU/PC), low-positive (1 to <11 RLU/PC), and high-positive (> or =11 RLU/PC) samples, respectively, were 0.91, 0.60, and 0.69 with PreservCyt and 0.93, 0.87, and 0.90 with STM. Our data showed high reliability and reproducibility with HC2, with values higher for STM than ThinPrep (Cytyc) samples.

Protocols for the assurance of microarray data quality and process control

Microarrays represent a powerful technology that provides the ability to simultaneously measure the expression of thousands of genes. However, it is a multi-step process with numerous potential sources of variation that can compromise data analysis and interpretation if left uncontrolled, necessitating the development of quality control protocols to ensure assay consistency and high-quality data. In response to emerging standards, such as the minimum information about a microarray experiment standard, tools are required to ascertain the quality and reproducibility of results within and across studies. To this end, an intralaboratory quality control protocol for two color, spotted microarrays was developed using cDNA microarrays from in vivo and in vitro dose-response and time-course studies. The protocol combines: (i) diagnostic plots monitoring the degree of feature saturation, global feature and background intensities, and feature misalignments with (ii) plots monitoring the intensity distributions within arrays with (iii) a support vector machine (SVM) model. The protocol is applicable to any laboratory with sufficient datasets to establish historical high- and low-quality data.

Single-point versus five-point biochemical method for determination of estrogen and progesterone receptors

Receptors for estrogen and progesterone are accepted by international consensus as biomarkers of breast carcinoma responsiveness to endocrine therapy. Numerous current studies are aimed at consideration of importance of "the new generation" of estrogen-regulated biomarkers in treatment of breast cancer patients. Simultaneous knowledge of all these biomarkers may help in medical decision making. However, the amount of tumor material available from breast carcinoma can make impossible determination of estrogenregulated biomarkes together with estrogen and progesterone receptors. To assess whether we could replace our current five-point ligand binding assay for measurement of estrogen and progesterone receptors with a single- point ligand binding assay, we compared simultaneous measurements in same samples of breast carcinomas by both methods. A linear regression analysis shows that single-point assay can be confidently used instead of five-point assay. In addition, there were no variations over time in estrogen and progesterone receptors phenotypes, as well as in estrogen and progesterone receptors contents determined by single-point assay. Accordingly, the results clearly demonstrate the validity of intralaboratory quality control and give a possibility for the establishment of interlaboratory quality control of single-point ligand binding assay.