Improper coverage factor to compare expanded uncertainty with allowable total error
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Hikmet Can Çubukçu
To the Editor,
Measurement uncertainty (MU) has come to the forefront since ISO 15189 compelled laboratorians to evaluate it for all measurement methods [1]. Various researchers have published some articles in Turkish Journal of Medical Biochemistry concerning the utility of measurement uncertainty for examining laboratory quality [2], [3], [4]. In relevant articles expanded measurement uncertainties were compared with the allowable total error. The allowable total error can be used as a specification limit for measurement uncertainty only if a proper coverage factor utilized in the calculation [1]. However, at first, authors multiplied combined standard uncertainty with coverage factor 2 to calculate expanded measurement uncertainty, then compared it with the allowable total error. It should be kept in mind that coverage factor “2” is a Z score for two-sided estimations at 95% confidence interval. The allowable total error is commonly calculated as “1.65* imprecision+bias” [5]. It is obvious that expanded measurement uncertainty with two-sided estimation does not correspond to allowable total error. Additionally, measurement uncertainty can exceed the specification limit due to the wrong coverage factor. Therefore, Z score “1.65” should be utilized as a coverage factor to compare with the allowable total error.
References
1. Westgard JO, Westgard SA. Measuring analytical quality: total analytical error versus measurement uncertainty. Clin Lab Med 2017;37:1–13.10.1016/j.cll.2016.09.001Search in Google Scholar PubMed
2. Bal C, Serdar MA, Güngör OT, Çelik HT, Abuşoğlu S, Uğuz N, et al. Biyokimya parametrelerinin ölçüm belirsizliğinin hesaplanması. Turk J Biochem 2014;39:538–43.Search in Google Scholar
3. Oğul Y, Şenyurt M, Altınkaynak K, Aksoy H, Akçay F. The evaluation of measurement uncertainty for TSH, FT4 and FT3 tests. Turk J Biochem 2015;13:89–94.Search in Google Scholar
4. Çelebiler A, Serin H, Güleç D, Karaca B. Measurement uncertainty in clinical biochemistry laboratories: practical application. Turk J Biochem 2011;36:362–6.Search in Google Scholar
5. Ricos C, Alvarez V, Cava F, García-Lario JV, Hernández A, Jiménez CV, et al. Current databases on biological variation: pros, cons and progress. Scand J Clin Lab Invest 1999;59:491–500.10.1080/00365519950185229Search in Google Scholar PubMed
Article note
Measurment uncertainty can be used as an indicator of laboratory quality by comparing with accepted limits. Measurement of uncertainty can be compared with allowable total error by using the proper coverage factor. The coverage factor seems to be utilized improperly in some articles published in Turkish Journal of Biochemistry.
©2018 Walter de Gruyter GmbH, Berlin/Boston
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- Frontmatter
- Research Articles
- Evaluation of Gas6 and sAxl levels during attacks and attack-free periods of familial Mediterranean fever
- Do ovarian reserve markers predict the subsequent pregnancy outcomes in women with recurrent pregnancy loss?
- Evaluation of the relationship between TNFα, sTNFR1, sTNFR2, sIL2R, IL6, neopterin with disease activity in ankylosing spondylitis
- Evaluation of biological variations in glucose and glycated hemoglobin levels in healthy individuals
- Assessment of vitamin D deficiency level by the physiological response of parathyroid hormone in Turkish adults
- The comparison of two glucose measurement systems: POCT devices versus central laboratory
- Can ursolic acid be beneficial against diabetes in rats?
- Pediatric reference intervals of free thyroxine and thyroid stimulating hormone in three different hospitals
- Comparison of ELISA and flow cytometry for measurement of interleukin-1 beta, interleukin-6 and tumor necrosis factor-α
- The effects of vitamin D supplementation on healthy and hypercholesterolemic rabbits on levels of OSI and paraoxonase
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- Letters to the Editor
- Laboratory errors in the measurement of spectrin levels: detection range
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