Measurement uncertainty for serum free light chain assays: Estimation and implication on result interpretation |
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| Authors: | Li Wang Pak Cheung R. Chan |
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| Affiliation: | 1. Department of Pathology and Molecular Medicine, Faculty of Health Sciences, McMaster University, Canada;2. Department of Clinical Pathology, Sunnybrook Health Sciences Centre, Canada;3. Department of Laboratory Medicine and Pathobiology, University of Toronto, ON, Canada;1. Department of Pathology and Laboratory Medicine, St. Paul''s Hospital, University of British Columbia, Vancouver, Canada;2. Department of Pathology and Immunology, Washington University School of Medicine, St Louis, MO, USA;3. Department of Pediatrics, Washington University School of Medicine, St Louis, MO, USA;1. Laboratory of Clinical Chemistry, Virgen de la Salud Hospital, Complejo Hospitalario de Toledo, Toledo, Spain;2. Department of Gastroenterology, Virgen de la Salud Hospital, Complejo Hospitalario de Toledo, Toledo, Spain;1. Department of Clinical Laboratory, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, 100730, China;2. Institute of Basic Medicine Sciences, Chinese Academy of Medical Sciences, School of Basic Medicine, Peking Union Medical College, 5 Dong Dan San Tiao, Beijing 100005, China;1. Département d''Anesthésie-Réanimation, Hôpital Saint-Louis Assistance Publique des Hôpitaux de Paris (AP-HP), Paris, France;2. Département d''Anesthésie-Réanimation, Hôpital Bichat-Claude Bernard, Assistance Publique des Hôpitaux de Paris (AP-HP), Paris, France;3. Laboratoire de Biochimie, Hôpital Bichat-Claude Bernard, Assistance Publique des Hôpitaux de Paris (AP-HP), Paris, France;1. Department of Clinical Biochemistry, D??kap? Y?ld?r?m Beyaz?t Training and Research Hospital, Ankara, Turkey;2. Department of Clinical Biochemistry, Numune Training and Research Hospital Ankara, Turkey;3. Ankara Branch of the Council of Forensic Medicine, Department of Chemistry, Ankara, Turkey |
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| Abstract: | ObjectivesTo estimate the measurement uncertainty (MU) and reference change value (RCV) for serum free light chain assays (sFLC), and to review their implications on result interpretation.Design and methodsData from 6 to 9 months of internal QC and up to 3.5 years of EQA results were collected retrospectively, on the Roche Modular P analyzer and Dade Behring BN II nephelometer from two independent laboratories. MU was estimated from its components related to imprecision and bias determinations, while RCV was calculated from the estimated MU and published values on biological variation.Results and ConclusionThe standard uncertainty related to imprecision for the FLC were similar between two instruments, ranging from ~ 4% to ~ 8%, so were the uncertainty related to bias, ranging between 24% and 44%. The overall MU with 95% coverage for Fκ, Fλ and their ratio (rFLC) were 55%, 87% and 103% (Modular P), and 49%, 76% and 91% (BNII) respectively. The RCVs with biological variation for Fκ, Fλ and rFLC were comparable between two instruments and averaged 106%, 138% and 173% respectively. The relatively method-independent MU reflected the sFLC limitations. For monoclonal gammopathy detection, the universal rFLC reference limits ± MU gave an effective range of 0.02–3.15 (BNII) (as compared to 0.26–1.65), revealing substantial diagnostic grey zones on both ends. When monitoring disease activity, a minimum change (RCV) of ~ 100% in FLC concentrations or ~ 170% in rFLC would be considered significant. Applying MU when interpreting sFLC results puts current diagnostic cut-offs into perspective, and highlights the importance of collating other clinical findings. |
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