Abstract Number: PB0588
Meeting: ISTH 2020 Congress
Background: Six sigma (6σ) concept has been put in statistical quality control (QC) radar to monitor the quality performance of analytical instruments. The 6σ depicts a standard deviation of process that should fit within the tolerance limits of the quality requirement. Generally, assay with high σ score (≥3.0) demonstrates better analytical performance and lower variability.
Aims: We aimed to measure our two-year sigma scores for our haemostasis assays using total allowable error (TEa) based on desirable biological variation (BV) data by the Analytical Quality Commission of the Spanish Society for Clinical Chemistry (SEQC, 2004).
Methods: Sigma scores for two routine analytes; Prothrombin Time (PT) and Activated Partial Thromboplastin Time (APTT) were measured by tabulating our two-year internal QC data at normal and pathological levels for two separate lots. Both assays were performed on STA-Compact Max (Stago, France) using Stago reagents (STA-Neoplastine and STA-PTT Automate).
Equation; σ=(TEa − bias)/CV (CV;Coefficient of variation) was used to measure sigma scores. Statistical indices i.e. CV and bias were obtained from internal QC data and external quality assurance programme that we had participated within the corresponding period.
Results: Based on TEa by desirable BV, we performed poorly for both assays at both levels in both years as our σ scores were between 1.0 to 2.3. However, we noticed that our σ scores were slightly better for normal level compared to pathological level. We also noticed both analytes demonstrating consistent σ scores in both years. In this study, we focused on 6σ determination using desirable BV data and demonstrated that applying 6σ concept on IQC data results in σ value below minimum acceptable value of 3.0.
| Year | Analyte | Quality Control Level | Number of data (n) | Mean | Standard Deviation (SD) | Coefficient of Variation (CV) | Bias (obtained from external quality assurance data) | Total allowable error, desirable biological variation (TEa for BV) | Sigma score |
| 2018 | Prothrombin Time (PT) | Normal | 240 | 12.9 | 0.3 | 2.2 | 0.3 | 5.3 | 2.3 |
| Pathological | 239 | 22.9 | 0.8 | 3.3 | 0.3 | 5.3 | 1.5 | ||
| Activated Partial Thromboplastin Time (APTT) | Normal | 241 | 34.9 | 0.7 | 2.0 | 1.7 | 4.5 | 1.4 | |
| Pathological | 242 | 59.5 | 1.5 | 2.5 | 1.7 | 4.5 | 1.1 | ||
| 2019 | Prothrombin Time (PT) | Normal | 182 | 13.4 | 0.3 | 2.3 | 0.4 | 5.3 | 2.1 |
| Pathological | 182 | 23.7 | 0.8 | 3.2 | 0.4 | 5.3 | 1.5 | ||
| Activated Partial Thromboplastin Time (APTT) | Normal | 181 | 35.4 | 0.7 | 1.9 | 2.0 | 4.5 | 1.3 | |
| Pathological | 181 | 66.1 | 1.6 | 2.4 | 2.0 | 4.5 | 1.0 |
[Sigma scores for analytes using total allowable error (TEa) based on desirable biological variation (BV) data ]
Conclusions: In our laboratory, unsatisfactory performances (σ≤3.0) were observed in our routine haemostasis assays. We are able to have an overview of our quality performance by utilizing sigma metrics as a standard of excellence.
To cite this abstract in AMA style:
Othman HRB. Sigma Metrics Scores for Routine Haemostasis Assays in a Small Laboratory [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/sigma-metrics-scores-for-routine-haemostasis-assays-in-a-small-laboratory/. Accessed September 27, 2023.« Back to ISTH 2020 Congress
ISTH Congress Abstracts - https://abstracts.isth.org/abstract/sigma-metrics-scores-for-routine-haemostasis-assays-in-a-small-laboratory/