[Analysis on vitamin B_1 and vitamin B_2 proficiency testing assessment in China disease control and prevention system].

OBJECTIVE: To evaluate the detection ability of vitamin B_1 and vitamin B_(2 )in rice flour in the laboratories of disease control and prevention system, by conducting the proficiency testing(PT)activity. METHODS: Before the vitamin B_1 and vitamin B_2 quality control samples were distributed to the laboratories of disease control and prevention system, the uniformity and stability of samples were analyzed by one-way ANOVO respectively. High performance liquid chromatography(HPLC) method was required to determine vitamin B_1(GB 5009.84-2016: determination of vitamin B_1 in food, first method as reference). HPLC method was also required to determine vitamin B_2(GB 5009.85-2016: determination of vitamin B_2 in food, first method as reference). Robust statistics analysis of proficiency testing result was conducted to evaluate laboratory testing ability through Z score. RESULTS: A total of 43 laboratories completed the proficiency testing. In all of the laboratories participated in the determination of vitamin B_(1 )and vitamin B_2, the total satisfactory rate of vitamin B_1 was 88.4%, while vitamin B_2 was 86.0%. CONCLUSION: The ability of vitamin B_1 and vitamin B_2 detection in disease control and prevention system in China is better than expected, and the testing ability of a few laboratory needs to be improved.

External quality assurance in the era of standardization.

Metrology in clinical chemistry aims to ensure the equivalence of measurement results from different in-vitro diagnostic measurement devices (IVD MD) for use in healthcare. The metrological traceability of measurement results to higher-order references is the cornerstone to achieving equivalent results. However, other fundamentals are also needed, including the commutability of reference materials and external quality assessment (EQA) materials for monitoring the equivalence of measurement results at the end-user level. This manuscript summarizes the findings and opinions expressed at the Joint Community for Traceability in Laboratory Medicine (JCTLM) workshop held on December 4-5, 2023. The workshop explored the relationship between EQA/proficiency testing and metrological traceability to higher-order references. EQA monitors the equivalence of measurement results from end-user IVD MDs. The workshop discussed the role and challenges of using EQA to improve and maintain the equivalence of measurement results. It also elucidated current developments in establishing the clinical suitability of laboratory results expressed as analytical performance specifications (APS).

Proficiency testing of diagnosis in histopathology and immunohistochemistry of breast pathology in China: results from a pilot work of National Single Disease Quality Control Program for breast cancer.

AIM: Pathologists are currently supposed to be aware of both domestic and international guidelines for breast cancer diagnosis, but it is unclear how successfully these guidelines have been integrated into routine clinical practice in China. Thus, this national proficiency testing (PT) scheme for breast pathology was set up to conduct a baseline assessment of the diagnostic capability of pathologists in China. METHODS: This national PT plan is designed and implemented according to the "Conformity assessment-General requirements for proficiency testing" (GB/T27043-2012/ISO/IEC 17043:2010). Five cases of breast cancer with six key items, including histologic type, grade, ER, PR, HER2, and Ki67, were selected for testing among 96 participants. The final PT results were published on the website of the National Quality Control Center for Cancer ( http://117.133.40.88:3927/cn/col22/362 ). RESULTS: Our study demonstrated that the median PT score was 89.5 (54-100). Two institutions with scores < 67 were deemed unacceptable. The accuracy of histologic type, ER, PR, HER2, and Ki67 was satisfactory (all > 86%). However, the histologic grade showed low accuracy (74.0%). The unacceptable results mainly included incorrect evaluation of histologic grade (36.7%), inaccurate evaluation of ER/PR/HER2/Ki67 (28.2%), incorrect identification of C-AD as IBC-NST (15.7%), inappropriate use of 1+/2+/3+ rather than staining percentage for ER/PR (6.1%), misclassification of ER/PR < 1% weak expression as positive staining (1.4%), and no evaluation of histologic grade in ILC, MC, and IMC (5.8%). CONCLUSIONS: our nationwide PT program exhibited a satisfactory baseline assessment of the diagnostic capability of pathologists in China. More importantly, we identify some areas for further improvement.

SPOT/Dx Pilot Reanalysis and College of American Pathologists Proficiency Testing for KRAS and NRAS Demonstrate Excellent Laboratory Performance.

CONTEXT.­: The Sustainable Predictive Oncology Therapeutics and Diagnostics quality assurance pilot study (SPOT/Dx pilot) on molecular oncology next-generation sequencing (NGS) reportedly demonstrated performance limitations of NGS laboratory-developed tests, including discrepancies with a US Food and Drug Administration-approved companion diagnostic. The SPOT/Dx pilot methods differ from those used in proficiency testing (PT) programs. OBJECTIVE.­: To reanalyze SPOT/Dx pilot data using PT program methods and compare to PT program data.Also see p. 136. DESIGN.­: The College of American Pathologists (CAP) Molecular Oncology Committee reanalyzed SPOT/Dx pilot data applying PT program methods, adjusting for confounding conditions, and compared them to CAP NGS PT program performance (2019-2022). RESULTS.­: Overall detection rates of KRAS and NRAS single-nucleotide variants (SNVs) and multinucleotide variants (MNVs) by SPOT/Dx pilot laboratories were 96.8% (716 of 740) and 81.1% (129 of 159), respectively. In CAP PT programs, the overall detection rates for the same SNVs and MNVs were 97.2% (2671 of 2748) and 91.8% (1853 of 2019), respectively. In 2022, the overall detection rate for 5 KRAS and NRAS MNVs in CAP PT programs was 97.3% (1161 of 1193). CONCLUSIONS.­: CAP PT program data demonstrate that laboratories consistently have high detection rates for KRAS and NRAS variants. The SPOT/Dx pilot has multiple design and analytic differences with established PT programs. Reanalyzed pilot data that adjust for confounding conditions demonstrate that laboratories proficiently detect SNVs and less successfully detect rare to never-observed MNVs. The SPOT/Dx pilot results are not generalizable to all molecular oncology testing and should not be used to market products or change policy affecting all molecular oncology testing.

Total error in lymphocyte subpopulations by flow cytometry-based in state of the art using Spanish EQAS data.

OBJECTIVES: Flow cytometry analyses of lymphocyte subpopulations (T, B, NK) are crucial for enhancing clinical algorithms and research workflows. Estimating the total error (TE) values for the percentage and absolute number of lymphocyte subpopulations using the state-of-the-art (SOTA) approach with real data from an external proficiency testing (EPT) scheme was performed. A comparison with previously published Biological Variability (BV)-based specifications was carried out. METHODS: A total of 44,998 results from 86 laboratories over 10 years were analysed and divided into two five-year periods (2012-2016) and (2017-2021). Data come from the IC-1 Lymphocytes scheme of the Spanish External Quality Assurance System (EQAS) GECLID Program. This quantitative scheme includes percentages and absolute numbers of CD3+, CD3+CD4+, CD3+CD8+, CD19+, and CD3-CD56+CD16+ NK cells. The percentage of TE was calculated as: |reported value - robust mean|*100/robust mean for each laboratory and parameter. The cut-off for TE is set at 80 % best results of the laboratories. RESULTS: A significant reduction in the SOTA-based TE for all lymphocyte subpopulations in 2017-2021 was observed compared to 2012-2016. The SOTA-based TE fulfils the minimum BV-based TE for percentages of lymphocyte subpopulations. The parameter with the best analytical performance calculated with SOTA (2017-2021 period)-based TE was the percentage of CD3+ (TE=3.65 %). CONCLUSIONS: The values of SOTA-based specifications from external quality assurance program data are consistent and can be used to develop technical specifications. The technological improvement, quality commitment, standardization, and training, reduce TE. An update of TE every five years is therefore recommended. TE assessment in lymphocyte subsets is a helpful and reliable tool to improve laboratory performance and data-based decision-making trust.

Accuracy-based proficiency testing for estradiol measurements.

OBJECTIVES: Accuracy of estradiol measurements is important but conventional proficiency testing (PT) cannot assess accuracy when possibly non-commutable samples are used and method peer-group means are the targets. Accuracy-based assessment of estradiol measurements is needed. DESIGN AND METHODS: Five serum samples were prepared from single donors, frozen, and distributed overnight to 76 New York State Department of Health (NYSDOH)-certified laboratories. Participants analyzed samples for estradiol. The biases of group means were assessed against the Centers for Disease Control and Prevention (CDC)-defined targets, evaluated using the Hormone Standardization Program (HoSt) E2 performance criterion of ±12.5 %. Each laboratory's performance was evaluated using total allowable error (acceptance limits) of target ±25 % or ±15 pg/mL (55 pmol/L) (whichever was greater, NYSDOH), target ±30 % (Clinical Laboratory Improvement Amendments [CLIA]), and target ±26 % (minimal limit based on biological variation [BV]). RESULTS: The biases (range) were 34 % (-17 % to 175 %), 40 % (-33 % to 386 %), 16 % (-45 % to 193 %), 5 % (-27 % to 117 %), and -4% (-31 % to 21 %), for samples at estradiol of 24.1, 28.4, 61.7, 94.1, and 127 pg/mL, or 89, 104, 227, 345, and 466 pmol/L, respectively. Large positive method/analytical systematic biases were revealed for 9 commonly used method/analytical systems in the United States at low estradiol concentrations. Of the 9 analytical systems, 0, 0, 3, 7 and 6 met the HoSt criterion for the samples with estradiol at the five respective concentrations. PT evaluation showed that 59 %, 69 % and 87 % of laboratories would receive a PT event passing (satisfactory) score when the CDC-defined target and a criterion of NYSDOH, CLIA or BV was used, respectively. However, >95 % laboratories would obtain PT passing score if method peer-group means were used as targets regardless of the criterion used. CONCLUSIONS: Improvement in accuracy of estradiol measurements is needed, particularly at low estradiol concentrations. Accuracy-based PT provides unambiguous information about the accuracy of methods/analytical systems.

Impact of Academia-Government Collaboration on Laboratory Medicine Standardization in South Korea: analysis of eight years creatinine proficiency testing experience.

OBJECTIVES: To evaluate the performance of the Academia-Government Collaboration for Laboratory Medicine Standardization in Korea (KR-STDZN) based on data from KR-STDZN proficiency testing (KR-STDZN-PT) for creatinine over eight years (2015-2022). METHODS: We used KR-STDZN-PT data of creatinine tests from 2015 to 2022. Acceptance of the participating institutions' test results was assessed by calculating the acceptance performance as absolute bias (absBias%), total coefficient of variance (tCV%), and total error (TE%) for each sample using six measurements from each institution and true values of each reference material. The test result was considered acceptable when absBias%, tCV%, and TE% were <5.10, <3.20, and <11.40 %, respectively. The proportion of acceptable institutions among all participating institutions in each round was defined as the acceptance rate. Improvements in absBias%, tCV%, and TE% were analyzed using creatinine concentration ranges in samples. RESULTS: The number of participating institutions increased from 2015 to 2017 but remained consistent since 2018. The acceptance rates for absBias% and TE% increased from 52.2 and 77.6 %, in 2015 and to 90.7 and 96.3 %, in 2022, respectively. The acceptance rate for tCV% remained in the 90 % range for eight years. When creatinine <3 mg/dL, mean absBias%, and mean TE% improved significantly in 2021-2022 compared to 2015-2016 (p<0.05). When creatinine >3 mg/dL, acceptance performance did not improve. Mean tCV% remained consistent annually regardless of creatinine concentration. No significant variations in test methods were observed. CONCLUSIONS: The collaboration between academia and the government improved creatinine testing quality. Nevertheless, KR-STDZN must be expanded and refined.

Recommendations for Setting a Criterion and Assessing Commutability of Sample Materials Used in External Quality Assessment/Proficiency Testing Schemes.

It is important for external quality assessment materials (EQAMs) to be commutable with clinical samples; i.e., they should behave like clinical samples when measured using end-user clinical laboratory in vitro diagnostic medical devices (IVD-MDs). Using commutable EQAMs makes it possible to evaluate metrological traceability and/or equivalence of results between IVD-MDs. The criterion for assessing commutability of an EQAM between 2 IVD-MDs is that its result should be within the prediction interval limits based on the statistical distribution of the clinical sample results from the 2 IVD-MDs being compared. The width of the prediction interval is, among other things, dependent on the analytical performance characteristics of the IVD-MDs. A presupposition for using this criterion is that the differences in nonselectivity between the 2 IVD-MDs being compared are acceptable. An acceptable difference in nonselectivity should be small relative to the analytical performance specifications used in the external quality assessment scheme. The acceptable difference in nonselectivity is used to modify the prediction interval criterion for commutability assessment. The present report provides recommendations on how to establish a criterion for acceptable commutability for EQAMS, establish the difference in nonselectivity that can be accepted between IVD-MDs, and perform a commutability assessment. The report also contains examples for performing a commutability assessment of EQAMs.

Development and application of proficiency testing (PT) to evaluate the diagnostic capacity of SARS-CoV-2 by RT-qPCR - A practical and metrological approach.

It is necessary to use quality tools to evaluate the diagnostic capacity of laboratories, such as implementing a proficiency testing (PT) program. The goal of this work is to develop and apply a PT protocol to assess the diagnostic capacity of SARS-CoV-2 through the RT-PCR method, based on appropriate metrological tools. A 5-item test panel containing items with different dilutions of SARS-CoV-2, including negative controls, was developed to perform this PT with the application of different performance assessment tools to score and differentiate performance between laboratories, according to Table 2. Based on the participants' total qualitative result, 95% of the negative samples and 73% of the positive samples were correctly identified by the laboratories. The results obtained were compared e validate the systematics of the PT developed, so that it can be implemented and used to monitor and improve the diagnostic capacity of SARS-CoV-2, also helping to improve the quality of these results.

Busulfan Interlaboratory Proficiency Testing Program Revealed Worldwide Errors in Drug Quantitation and Dose Recommendations.

BACKGROUND: The clinical outcomes of busulfan-based conditioning regimens for hematopoietic cell transplantation (HCT) have been improved by personalizing the doses to target narrow busulfan plasma exposure. An interlaboratory proficiency test program for the quantitation, pharmacokinetic modeling, and busulfan dosing in plasma was developed. Previous proficiency rounds (ie, the first 2) found that 67%-85% and 71%-88% of the dose recommendations were inaccurate, respectively. METHODS: A proficiency test scheme was developed by the Dutch Foundation for Quality Assessment in Medical Laboratories (SKML) and consisted of 2 rounds per year, with each round containing 2 busulfan samples. In this study, 5 subsequent proficiency tests were evaluated. In each round, the participating laboratories reported their results for 2 proficiency samples (ie, low and high busulfan concentrations) and a theoretical case assessing their pharmacokinetic modeling and dose recommendations. Descriptive statistics were performed, with ±15% for busulfan concentrations and ±10% for busulfan plasma exposure. The dose recommendations were deemed accurate. RESULTS: Since January 2020, 41 laboratories have participated in at least 1 round of this proficiency test. Over the 5 rounds, an average of 78% of the busulfan concentrations were accurate. Area under the concentration-time curve calculations were accurate in 75%-80% of the cases, whereas only 60%-69% of the dose recommendations were accurate. Compared with the first 2 proficiency test rounds (PMID 33675302, October, 2021), the busulfan quantitation results were similar, but the dose recommendations worsened. Some laboratories repeatedly submit results that deviated by more than 15% from the reference values. CONCLUSIONS: The proficiency test showed persistent inaccuracies in busulfan quantitation, pharmacokinetic modeling, and dose recommendations. Additional educational efforts have yet to be implemented; regulatory efforts seem to be needed. The use of specialized busulfan pharmacokinetic laboratories or a sufficient performance in busulfan proficiency tests should be required for HCT centers that prescribe busulfan.

Advancing proficiency testing for ultra in resource-limited settings using dried tube specimen: A study by SRL-Uganda.

BACKGROUND: Proficiency testing (PT) has been hard to set up due to cost limitations and technical capacity. Conventional Xpert MTB/RIF PT programs use liquid and culture spots which require stringent storage and transportation conditions with cross-contamination chances prevalent. These setbacks prompted the use of dried tube specimens (DTS) for Ultra assay PT. For continuity of PT provision, stability of DTS and compatibility with testing protocols when kept for a long period needs to be established. METHODS: DTS were prepared from known isolates inactivated using a hot air oven at 85°C. 100µl of bacterial suspensions were aliquoted and dried inside a Biosafety cabinet. Panel validation was done to establish the baseline Deoxyribonucleic acid (DNA) concentration in terms of cycle threshold (Ct) value. DTS aliquots were shipped to participants to test and report within six weeks. The remaining DTS were kept at 2-8°C and room temperature for one year with testing at six months. Twenty (20) DTS samples per set remaining at one year were heated at 55°C for two weeks before testing. The means of the different samples were compared to validation data using paired t-tests. Boxplots were designed to visualize the differences in the medians of the DTS. RESULTS: Overall mean Ct value increased by 4.4 from the validation to testing after one year at the different storage conditions. Samples heated at 55°C showed a 6.4 Ct difference from validation data. Testing done at six months on 2-8°C stored items showed no statistical difference. At all the remaining testing times and conditions, P-values were less than 0.008 although the absolute mean Ct when compared showed slight increments and accommodated differences for the detection of MTB and rifampicin resistance. Median values for samples stored at 2-8°C were lower compared to those at room temperature. CONCLUSION: DTS stored at 2-8°C remain more stable for one year compared to higher temperatures and can be consistently used as PT materials in more than one PT round for biannual PT providers.

Survival of Salmonella spp. and Pathogenic Escherichia coli in Food Matrixes and Its Relevance in the Development of Proficiency Testing Samples.

Monitoring of food products by government agencies for their compliance to regulatory limits is an essential step in controlling foodborne outbreaks. For monitoring purposes, an extensive setup of the surveillance system is used, which involves ISO 17025:2017 accredited laboratories for food testing. Participation in proficiency testing (PT) programs is a requirement of ISO 17025:2017, which ensures data accuracy and analyst competency. Participation in PT schemes is costly for laboratories in developing countries as most of the commercial suppliers are situated in the United States and Europe. The literature or data available on creation of microbiological proficiency testing is scanty as much of the data available with commercial suppliers are trade secrets, and there is only 0.06% of research articles available in the Scopus database on the topic. In this review article, an attempt is made to understand the factors impacting the survival of two important foodborne pathogens, i.e., Escherichia coli and Salmonella spp., by extracting information available from growth studies and root-cause analysis of various food safety incidents and recalls. Utilization of this information in the development of PT samples is discussed in this review article along with a focus on the availability of PT samples and associated ISO standards to formulate homogeneous and stable PT samples. This review article elaborates on the focus areas that can be considered by PT providers (PTP)-for example, initial inoculum level and preparation, strain type, microbial growth phase, the impact of different types of food matrixes including low-moisture food, antimicrobial components, pH, presence of competitor microbes, and environmental conditions involving storage temperature, time, and relative humidity. These focus areas can be used to successfully create PT samples by PTP in developing countries.

Nicotine and Tobacco Alkaloid Testing and Challenges: Lessons Learned From a College of American Pathologists Proficiency Testing Survey.

CONTEXT.­: Consequences related to nicotine (NIC) use remain a major health concern, leading to demand for testing to detect NIC, metabolites such as cotinine (COT), and related tobacco alkaloids, including anabasine (ANAB). NIC-related testing is not standardized among laboratories, nor are there clinical or regulatory guidelines to inform decisions such as appropriate screening cutoffs or limits of quantitation. OBJECTIVE.­: To evaluate analytical performance and reporting practices of laboratories that perform NIC-related testing by reviewing participant responses to the Nicotine and Tobacco Alkaloid (NTA) Proficiency Testing Survey. DESIGN.­: NTA results were retrieved from 2017 (the first year of the survey) through 2020. Survey participants, methodologies, and results were evaluated for all analytes, and simulated grading was performed for COT. Additional data, including limits of quantitation, qualitative cutoffs, and reasons for testing, were reviewed. RESULTS.­: Participant growth was steady for qualitative COT testing. Participation was stable for NIC, ANAB, and quantitative COT testing. Overall, participants performed well on survey challenges. However, reporting thresholds were widely divergent, ranging from 10 to 3000 ng/mL and 0.5 to 300 ng/mL, respectively, for qualitative and quantitative COT testing. Screening cutoffs were as high as 100 ng/mL for ANAB and 1000 ng/mL for NIC. CONCLUSIONS.­: Although participating laboratories performed well on the NTA Survey, the wide diversity of qualitative and quantitative reporting thresholds creates substantial risk for misinterpretation of results, and could lead to analytical concerns such as excessively high false-negative or false-positive rates. NIC-related testing would benefit from evidence-based guidelines to drive standardization of reporting.

Four-Year Laboratory Performance of the First College of American Pathologists In Silico Next-Generation Sequencing Bioinformatics Proficiency Testing Surveys.

CONTEXT.­: In 2016, the College of American Pathologists (CAP) launched the first next-generation sequencing (NGS) in silico bioinformatics proficiency testing survey to evaluate the performance of clinical laboratory bioinformatics pipelines for the detection of oncology-associated variants at varying allele fractions. This survey focused on 2 commonly used oncology panels, the Illumina TruSeq Amplicon Cancer Panel and the Thermo Fisher Ion AmpliSeq Cancer Hotspot v2 Panel. OBJECTIVE.­: To review the analytical performance of laboratories participating in the CAP NGS bioinformatics (NGSB) surveys, comprising NGSB1 for Illumina users and NGSB2 for Thermo Fisher Ion Torrent users, between 2016 and 2019. DESIGN.­: Responses from 78 laboratories were analyzed for accuracy and associated performance characteristics. RESULTS.­: The analytical sensitivity was 90.0% (1901 of 2112) for laboratories using the Illumina platform and 94.8% (2153 of 2272) for Thermo Fisher Ion Torrent users. Variant type and variant allele fraction were significantly associated with performance. False-negative results were seen mostly for multi-nucleotide variants and variants engineered at variant allele fractions of less than 25%. Analytical specificity for all participating laboratories was 99.8% (9303 of 9320). There was no statistically significant association between deletion-insertion length and detection rate. CONCLUSIONS.­: These results demonstrated high analytical sensitivity and specificity, supporting the feasibility and utility of using in silico mutagenized NGS data sets as a supplemental challenge to CAP surveys for oncology-associated variants based on physical samples. This program demonstrates the opportunity and challenges that can guide future surveys inclusive of customized in silico programs.

Clinical Testing for Tumor Cell-Free DNA: College of American Pathologists Proficiency Programs Reveal Practice Trends.

CONTEXT.­: Clinical testing for tumor cell-free DNA (cfDNA) has evolved rapidly, but no practice guidelines exist. OBJECTIVE.­: To summarize cfDNA laboratory practices based on self-reporting and assess preanalytical, analytical, and postanalytical trends that may influence the quality, accuracy, and consistency of cfDNA testing. DESIGN.­: Data were derived from the College of American Pathologists cfDNA proficiency testing program submitted by 101 participating laboratories from 2018 to 2019. RESULTS.­: Most laboratories performing clinical circulating tumor DNA testing are commercial/nonhospital (71.2%; 72 of 101) and international (77.2%; 78 of 101) laboratories. Commercial laboratories had higher monthly test volumes than hospital-based laboratories (median, 36 versus 7-8) and tended to have larger gene panels (median, 50 versus 11 genes) when panel-based testing was offered. The main clinical indications include therapy selection and treatment/disease monitoring. Plasma is the most commonly accepted specimen, which is predominantly collected in cell-stabilizing tubes. Equal proportions of laboratories use next-generation sequencing (NGS) and non-NGS methods to assess key genes, including EGFR, BRAF, KRAS, NRAS, and IDH1. Most laboratories reported a lower limit of detection (LLOD) of 0.5%, variant allele frequency or less, which did not differ by method, NGS or non-NGS, except for EGFR. Sixty-five percent (17 of 26) of laboratories using the US Food and Drug Administration (FDA)-approved non-NGS EGFR assay report analytical sensitivities higher than 0.5%, as compared to 15% (16 of 104) of laboratories using an alternative NGS or non-NGS method. There is also a wider range in LLODs obtained for the FDA-approved EGFR assay than nonapproved assays. CONCLUSIONS.­: These results highlight emerging practice trends and serve as a foundation to initiate future practice recommendations.

Piloting a Proficiency Testing Program for Laboratory Sampling of Animal Feed Materials.

BACKGROUND: Laboratory sampling is a significant source of error in feed testing. Proficiency testing programs such as the Association of American Feed Control Officials Proficiency Testing Program are an effective means of assessing error in and among analytical methods. However, all proficiency test items are comminuted and blended to control variability among items, effectively minimizing sampling error. Currently there is no mechanism for monitoring sampling error among laboratories. OBJECTIVE: The objective of this work was to investigate the feasibility of a proficiency testing program for laboratory sampling methods and provide insight into a program to advance the performance of sampling in laboratories. METHODS: The study involved the fabrication of identical feed test items from feed ingredients and shipping the uncomminuted materials to volunteer laboratories. The volunteer laboratories followed in-house procedures for selecting test portions for routine feed tests. Tests on all the test portions for a single analyte were performed by a single laboratory, so that the variability in test results could be attributed to laboratory sampling processes to select test portions. RESULTS: The average RSD, %, for Item A and Item B, respectively, were as follows: protein, 5.08 and 5.23; non-protein nitrogen, 8.90 and 16.6; crude fat, 3.45 and 5.67; vitamin A, 33.9 and 26.9; calcium, 21.9 and 23.6; zinc, 17.9 and 27.9; and copper, 17.4 and 27.9. CONCLUSION: This study suggests that a proficiency testing program for laboratory sampling is feasible with manual manufacture of the test items, and data can be used to monitor laboratory sampling proficiency and also to compare the performance of different laboratory sampling methods. HIGHLIGHTS: The data illustrates that each analyte has unique distributional and compositional heterogeneity, thus unique sampling error, even when multiple analytes are determined from a single test portion.