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| ORIGINAL ARTICLE |
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| Year : 2023 | Volume
: 9
| Issue : 1 | Page : 25-28 |
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Six Sigma metrics as an indicator for Randox International Quality Assessment Scheme in clinical biochemistry laboratory: A pilot study with thyroid function test in a tertiary care hospital
Neeraj Yadav, Mukesh Kumar Meena, Shailata Prisi, Aditi Singh, Ritu Singh
Department of Biochemistry, Lady Hardinge Medical College, New Delhi, India
| Date of Submission | 01-Feb-2023 |
| Date of Acceptance | 30-Mar-2023 |
| Date of Web Publication | 28-Apr-2023 |
Correspondence Address:
Dr. Aditi Singh
Department of Biochemistry, Lady Hardinge Medical College, Connaught Place, Bharat Singh Marg, New Delhi 110001
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/mamcjms.mamcjms_12_23
Context: Six Sigma methodology represents an evolution in quality assessment and management that has been implemented widely in industry and health sector since the mid-1980s. It consists of five steps: define, measure, analyze, improve, and control (DMAIC). Randox International Quality Assessment Scheme (RIQAS) program Target Score (TS) is a performance indicator, and Sigma metrics is considered as a gold standard for overall performance. Aim: The aim of this study is to present the TS and Sigma metrics observed in clinical chemistry laboratory in SSK Hospital associated with Lady Hardinge Medical College to evaluate the analytical performance of T3, T4, and thyroid-stimulating hormone (TSH) parameters. The study period is from June to August 2022. Materials and Methods: The Sigma metrics for the various analytes was calculated by the following equation: Σ = TEa − bias/CV (TEa—total allowable error, CV—coefficient of variation). Acceptable performance criteria: standard deviation index (SDI) <2; TS >50; the closer a value is to 120, the better the performance, <40 is unacceptable; and %deviation should be less than the defined acceptable limits which is unique to each analyte, the closer the value is to zero, the better is the performance. Results: Our RIQAS results lie in acceptable range except for T3 in the month of August in which TS was unacceptable. Our laboratory Sigma metrics were below three sigmas. The findings of our exercise emphasize the need for a detailed evaluation, and we promote the use of Sigma metrics in quality assurance in the best interest of the patient. Conclusion: Quality check strategies were applied according to the TS and sigma values.
Keywords: Randox International Quality Assessment Scheme (RIQAS), Sigma metrics, Target score (TS), Thyroid function test, Quality control (QC)
How to cite this article:
Yadav N, Meena MK, Prisi S, Singh A, Singh R. Six Sigma metrics as an indicator for Randox International Quality Assessment Scheme in clinical biochemistry laboratory: A pilot study with thyroid function test in a tertiary care hospital. MAMC J Med Sci 2023;9:25-8 |
How to cite this URL:
Yadav N, Meena MK, Prisi S, Singh A, Singh R. Six Sigma metrics as an indicator for Randox International Quality Assessment Scheme in clinical biochemistry laboratory: A pilot study with thyroid function test in a tertiary care hospital. MAMC J Med Sci [serial online] 2023 [cited 2023 Jun 4];9:25-8. Available from: https://www.mamcjms.in/text.asp?2023/9/1/25/375330 |
| Introduction | |  |
Quality is defined as conformance to the requirements of users or customers and the satisfaction of their needs and expectations.[1] Quality management in clinical laboratories encompasses quality laboratory processes, quality control (QC), quality assessment, and quality improvement. QC not only ensures the accuracy and precision of the analytical process but also detects any kind of immediate error, hence ensures the accuracy and precision of the analytical process. External QC (EQC) and internal QC (IQC) both form an important part of overall QC assessment. IQC, done at regular intervals, is used for ensuring the continuous monitoring of the analytical system, whereas, EQC, which is supplied by an external agency, helps in evaluating the laboratory performance compared to peer laboratories using the same methodologies, instruments, and reagents.[2]
Motorola first developed the concept of Six Sigma in the early 1980s, which was thereafter also introduced into healthcare systems.[3] Six Sigma is a management strategy which measures the performance of the processes as a rate of defects per million opportunities (DPM or DPMO) and helps in improving the quality of process outputs. International Organization for Standardization (ISO) defines these defects as nonconformances. The aim of Six Sigma strategy is to decrease the variation within a program by error measurement followed by analysis, ultimately leading to strategy formulation in improving the process.[2] Six Sigma consists of five steps: define, measure, analyze, improve, and control (DMAIC). It reflects the international level of quality. Laboratories with world-class quality performance are expected to meet Six Sigma level defined by approximately 3.4 DPMO, signifying 99.99966% of results as error free.[3]
Thyroid dysfunction having wide clinical implication is quite commonly encountered in medical practice. Efficient biochemical testing will help the clinicians in making timely and accurate clinical decisions, as patients with thyroid disorders generally present with vague nonspecific symptoms. Therefore, using IQC and EQC along with Six Sigma will improve the laboratory performance, giving more accurate results and benefiting the patient care.
| Aim | | |
The aim of this study is to present the Target Score (TS) and Sigma metrics observed in the clinical biochemistry laboratory in SSK Hospital associated with Lady Hardinge Medical College to evaluate the analytical performance of T3, T4, and thyroid-stimulating hormone (TSH) parameters.
| Materials and Methods | | |
It was a retrospective study conducted in the Department of Biochemistry, Lady Hardinge Medical College, New Delhi for the period of 3 months (June to August 2022). The serum samples were run for biochemical parameters included in thyroid profile (i.e., free T3, free T4, and TSH) after daily QC on UniCel DxI 800 Access Immunoassay System. Westgard rules were applied for the interpretation of daily IQC results. Westgard rules of 1 3s, 2 2s, R4s, 4 1s, and 10x were considered as rejection and 1 2s as warning situations for the respective run. Our laboratory participates monthly in the EQC survey of Randox International Quality Assessment Scheme (RIQAS, Randox Laboratories, United Kingdom) from which we retrieve the TS, standard deviation index (SDI), and %deviation results calculated from the peer group data.
TS = log10(3.16 × Target deviation for performance assessment (TDPA) ÷ %dev) 100
Acceptable performance criteria: SDI <2; TS >50; the closer a value is to 120, the better the performance, <40 is unacceptable; and %deviation should be less than the defined acceptable limits which is unique to each analyte, the closer the value is to zero, the better is the performance. TDPAs are fit-for-purpose performance criteria which are set taking guidance from ISO/IEC17043, ISO13528, and International Union of Pure and Applied Chemistry (IUPAC).
Total Allowable Error
TEa measures the impact of imprecision and bias on test result, and its effect on clinical decisions in respect to further investigations and treatment. Clinical Laboratory Improvement Amendment (CLIA)-88 Proficiency Testing Criteria define analytical quality requirements in terms of “TEa” for acceptable performance for each analyte. Ricos et al.[4] provided an extensive listing of reference values in accordance the with CLIA guidelines.
Bias
Bias is inversely related to the trueness and is calculated as the difference between the average value and the true value. Bias was taken from percentage of deviation of the peer group data from results returned from RIQAS.
Bias (%) = (mean of all laboratories using same instrument and method − our mean)/mean of all laboratories using the same instrument and method) × 100
Coefficient of Variance
Coefficient of variance (CV) gives an idea about the performance of a method. CV% provides degree of precision from statistical imprecision measures. CV was determined from the calculated laboratory mean and calculated standard deviation (SD) retrieved from the IQC data over the 3 months:
CV (%) = (SD/Laboratory mean) × 100
CVs ≤5% indicate a good performance method, whereas CVs of 10% and higher imply unsatisfactory performance.
The Sigma metrics for the various analytes was calculated by the following equation:
∑(σ) = (TEa − bias)/CV
Sigma scale helps to assesses the quality with 3 sigma being allowable for routine performance and a sigma of 6 for world-class quality.[5]
All calculations were done in MS Excel of Windows 10.
| Results | | |
We ran RIQAS for the months of June, July, and August, from which we retrieved the TS, SDI, and %deviation results. TS for free T3 was acceptable for the months of June and July with values 91 and 59, respectively; however, for the month of August, it was 23 which was out of acceptable criteria. TS for free T4 was acceptable for the months of June, July, and August with values 50, 111, and 70, respectively. TS for TSH was acceptable for the months of June, July, and August with values 54, 120, and 87, respectively. TSH reached its peak performance with the TS of 120 in the month of July. Sigma score for free T3 for the months of June, July, and August was 0.6, −0.1, and −1.6, respectively. Similarly, the Sigma score for free T4 for the months of June, July, and August was −0.7, 0.5, and −0.5, respectively. However, Sigma score for TSH showed better performance consistently for the months of June, July, and August with values of 2.7, 4.0, and 3.5, respectively [Table 1],[Table 2],[Table 3]. | Table 1 Monthwise Standard Deviation Index, %Dev, and Target Score Results from Randox International Quality Assessment Scheme.
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 | Table 2 Monthly Bias, Coefficient of Variance, and Sigma Metrics for Thyroid Function Test.
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| Discussion | | |
Laboratory results can be assessed by RIQAS reports which provide statistically robust consensus means and thereby identify acceptable and poor performance using performance indicators: %deviation, SDI, and TS. Percentage (%) deviation evaluates the concentration-related biases, and TS gives the numerical index of performance, allowing at-a-glance assessment. The sample variation due to homogeneity of sample, reconstituted stability, real-time stability, and shipping/transport stability is estimated by TDPA, which gives the upper deviation limit of performance for any parameter. TDPAs are reviewed regularly and deemed fit for purpose by the RIQAS Advisory Panel.[6]
The External Quality Assurance Scheme (EQAS) results for 3 months showed two thirds of good performances for the three thyroid function testing parameters as summarized in [Table 4]. In June, the three tests were performing well, but the Sigma score was less than three. In July, RIQAS results showed overall good performance, particularly TSH Sigma score was more than three. In August, T4 and TSH showed good performance but T3 was having a very low TS; and SDI, %deviation were outside acceptable limits. The performance of TSH was good for all the months of the study. However, our laboratory Sigma metrics were below three sigma. There is a need for review of analytical process if poor performance occurs over a long period of time across several samples, which may be due to a systematic error. However, poor performance for a single sample could be attributed to random error.
TEa values significantly affect sigma calculation. We have different assigned values for a single analyte. Thus, if the TEa of the parameter is at the higher side then there are more chances to get a good sigma value, and to choose a TEa source is a choice of the laboratory. Unfortunately, there is neither standardization nor harmonization of the existing resources for TEa goals.[5]
For the analytes having less than three sigma value, Westgard sigma rules recommend a revision in the daily workload division, and a change in the frequency of daily runs. For a more stringent QC practice, we also need to run two or three levels of daily controls covering range of the clinical decisive limits, for every analyte.[7] False rejection rate should also be kept in mind, which can be minimized by relaxing control limits up to 3 SDs.[8] Most clinical diagnostic laboratories are content if their results enclose ±2 SD or ±3 SD limits. Simply, they find defect rates of 45, 400 DPMO, and 2, 700 DPMO as acceptable performance.
This study presents the Sigma metrics of UniCel DxI 800 Access Immunoassay System analytical process results. Sigma metrics take into consideration of overall quality by combining the IQC (imprecision, CV) and the EQC (inaccuracy: bias) assessments. These results are helpful in applying the QC strategies to optimize the QC procedures and reduce the analytical variance, thus improving the overall quality assurance. As we have been taking the help of Westgard sigma rules, QC protocol needed to be customized for better outcome as well as consistent performance in thyroid function tests.
| Conclusion | | |
Our laboratory performance for T3, T4, and TSH was explored in the study using Six Sigma metrics. Sigma values of TSH were consistently satisfactory during this study. To conclude, Six Sigma methodology is an effective tool for evaluating the performance of biochemical analytes, but it’s a challenge to get and maintain good sigma value for those who have low TEa%. By proper selection of TEa, QC strategy, and the EQAS program and by keeping the CV and bias to the minimum, it’s highly likely that any laboratory would achieve a perfect reporting of Six Sigma standard, which must be a continuous practice.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
| References | | |
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| 4. | Ricos C, Alvarez V, Cava F et al. Current databases on biological variation: pros, cons and progress. Scand J Clin Lab Invest 1999;59:491–500. |
| 5. | Singh B, Goswami B, Gupta VK, Chawla R, Mallika V. Application of sigma metrics for the assessment of quality assurance in clinical biochemistry laboratory in India: a pilot study. Indian J Clin Biochem 2011;26:131-5. |
| 6. | Rentapalli BR, Ganji SB, Sulemani MD. Target score of RIQAS and sigma metrics for evaluating the analytical performance of thyroid function testing on ADVIA Centaur XPT immunoassay analyser. J Evol Med Dent Sci 2019;8:447-51. |
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[Table 1], [Table 2], [Table 3], [Table 4]
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