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Licensed Unlicensed Requires Authentication Published by De Gruyter October 21, 2021

External quality assessment of serum indices: Spanish SEQC-ML program

Rubén Gómez Rioja ORCID logo, Monserrat Ventura, María Antonia Llopis, Josep Miquel Bauça, Andrea Caballero Garralda, Mercedes Ibarz ORCID logo, Debora Martinez, Carolina Gómez, Paloma Salas Gómez-Pablos, Isabel García del Pino, Jose Delgado, Juan Jose Puente and Iciar Marzana



Serum indices included in clinical chemistry instruments are widely used by laboratories to assess the quality of samples. Instruments that report quantitative results allow an evaluation of their diagnostic performance in a similar way to other biochemical tests. The Spanish Society of Laboratory Medicine (SEQC-ML) launched a monthly External Quality program of serum indices in 2018 using three lyophilized materials of simultaneous annual distribution. We present the results of the first three years of the program.


The use of four different quality control materials with different concentrations in three alternate months allows an annual evaluation of the participant’s accuracy. Assigned values are established by consensus among homogeneous groups, considering necessary at least 10 participants for a comparison at instrument level. The average percentage difference results per instrument allow the assessment of bias among groups.


The imprecision of the three indices ranges between 3 and 9%, with no major differences among instruments. Significant differences were observed in all indices among instruments with more than 10 participants (Roche Cobas, Abbott Architect, Abbott Alinity and Siemens Advia). The 90th percentile of the distribution of percentage differences was used as the analytical performance specification (APS). An improvement in performance was observed in the first three years of the program, probably due to the learning curve effect. In 2020, APS of 7.8, 12.2 and 9.7% were proposed for hemolytic, icteric and lipemic indices, respectively.


Serum indices have a great impact on the quality and the reliability of laboratory test results. Participation in proficiency testing programs for serum indices is helpful to encourage harmonization among providers and laboratories.

Corresponding author: Rubén Gómez Rioja, Laboratory Medicine, La Paz – Cantoblanco – Carlos III University Hospital, Madrid, Spain, E-mail:


The design and maintenance of the Quality Assurance Schemes of the Spanish Society of Laboratory Medicine (SEQC ML) is carried out by the Programs Committee, composed by: Ma Carmen Perich Alsina (President); Beatriz Boned Juliani; Sandra Bullich Marín; Marià Cortés Rius; Pilar Fernández Calle; Rubén Gómez Rioja; Ma Antonia Llopis Díaz; Cecília Martínez Bru; Francisco Ramón Bauzá; Ángel Salas García; Margarida Simon Palmada; Montserrat Ventura Alemany.

  1. Research funding: None declared.

  2. Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission.

  3. Competing interests: Authors state no conflict of interest.

  4. Informed consent: Not applicable.

  5. Ethical approval: Not applicable.


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Received: 2021-07-11
Accepted: 2021-09-24
Published Online: 2021-10-21
Published in Print: 2022-01-26

© 2021 Walter de Gruyter GmbH, Berlin/Boston

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