Chiscano‑Camón et al. Nutrition Journal (2022) 21:48 https://doi.org/10.1186/s12937-022-00803-y LETTER TO THE EDITOR Open Access Pre‑analytical and analytical procedures to avoid loss of vitamin C. Comment on: “COVID‑19: up to 82% critically ill patients had low vitamin C values” Luis Chiscano‑Camón1,2,3 , Juan Carlos Ruiz‑Rodriguez1,2,3*, Roser Ferrer4, Sílvia Camós4, Adolf Ruiz‑Sanmartin1,2,3 and Ricard Ferrer1,2,3 Main text 2.643 g for 10 min and stored frozen at − 20 °C protected We have read with great interest the short report by from light until their analysis (within 7 days of arrival - Tomasa – Irriguible et al. about the vitamin C levels in stability of the vitamin C molecule is 7 days at − 15 °C). critically ill COVID-19 adult patients with ARDS [1]. It To extract and stabilize vitamin C an equal volume refers to our study, in which it was found that in patients of cold metaphosphoric acid was added to the samples with ARDS caused by COVID-19, vitamin C levels while kept on ice bath and protected from light exposure. were extremely low [2]. However, the results of our study Plasma vitamin C was analyzed by a reversed-phase high- are questioned on the basis that according to Tomasa – performance liquid chromatography (HPLC) method Irriguible et al., the veracity of the methodology used to with photodiode detector (wavelength set to 245 nm). assess the vitamin C status of the patients was not clear, The method was fully validated in terms of linearity (1.5– so the values could be artifactually low. 30 mg/L), imprecision (less than 5%) and accuracy [5]. According to the literature, vitamin C is a very unstable The differences observed between the series by water-soluble micronutrient which can be easily oxidized Tomasa-Irriguible et al. and ours can be explained by or hydrolyzed [3]. We agree with the authors that the three reasons. First of all, the timing of the sample col- determination of vitamin C levels requires very rigorous lection; thus we consider this the most important con- pre-analytical and analytical procedures to avoid loss of sideration regarding the difference in the results. While vitamin. In our study we followed the recommendations they studied vitamin C in the first 24 hours after ICU published by Pullar et al. [4] and we performed the pre- admission, our study reported vitamin C serum levels at analytical phase with great care. 17.5 ± 1.7 days from admission to ICU. Second, the levels In our case, venous blood was collected into a 4 mL vac- considered low by Tomasa (0.14 ± 0.05 mg / dL) would uette tube with anticoagulant lithium heparin and imme- have been considered undetectable by the stoppage limit diately delivered to the laboratory protected from light. of our laboratory. So if their patients had been studied Two aliquots of plasma were separated in a centrifuge at by our detection threshold, there would be 65 patients (82%) who would present undetectable levels. Third, our patients had a higher degree of lung inflammation. In our *Correspondence: ruizrodriguezjc@gmail.com series, 94.4% of patients required prone position with 1 Intensive Care Department, Vall d’Hebron Hospital Universitari, Vall d’Hebron ­PaO2/FiO2 ratio at the time of vitamin C measurement Barcelona Hospital Campus, Barcelona, Spain of 94.4 ± 5.9, unlike the series with which we compared Full list of author information is available at the end of the article © The Author(s) 2022. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://​creat​iveco​mmons.​org/​licen​ses/​by/4.​0/. The Creative Commons Public Domain Dedication waiver (http://​creat​iveco​ mmons.​org/​publi​cdoma​in/​zero/1.​0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Chiscano‑Camón et al. Nutrition Journal (2022) 21:48 Page 2 of 2 ourselves, where only 49 (73.1%) required mechanical Vall d’Hebron University Hospital, Vall d’Hebron Barcelona Hospital Campus, Barcelona, Spain. ventilation. We consider that our preanalytical processing of the Received: 13 November 2021 Accepted: 20 July 2022 samples for the analysis of vitamin C was carried out under conditions that guarantee the absence of oxida- tion of vitamin C and stability of the sample through- out the whole process. The method is robust for clinical References measurement of vitamin C in plasma specimens. Con- 1. Tomasa-Irriguible T, Bielsa-Berrocal L. COVID-19: up to 82% critically ill patients had low vitamin C values. Nutr J. 2021;20:66. sequently, the results of our study should be considered 2. Chiscano-Camón L, Ruiz-Rodriguez JC, Ruiz-Sanmartin A, Roca O, Ferrer R. correct. Vitamin C levels in patients with SARS-CoV-2-associated acute respiratory distress syndrome. Crit Care. 2020;24:522. 3. Karlsen A, Blomhoff R, Gundersen TE. Stability of whole blood and plasma Abbreviations ascorbic acid. Eur J Clin Nutr. 2007;61:1233–6. ARDS: Acute Respiratory Distress Syndrome; COVID-19: Coronavirus Infectious 4. Pullar JM, Bayer S, Carr AC. Appropriate handling, processing and analysis Disease 2019; ICU: Intensive Care Unit; ml: Milliliters; PaO2/FiO2 ratio: Arterial of blood samples is essential to avoid oxidation of vitamin C to Dehy‑ oxygen pressure (PaO2), inspired fraction of oxygen (FIO2); SARS-CoV-2: Severe droascorbic acid. Antioxidants. 2018;7(2):29. acute respiratory syndrome Coronavirus-2. 5. Collie JTB, Greaves RF, Jones OAH, Eastwood G, Bellomo R. Vitamin C measurement in critical illness: challenges, methodologies and quality Acknowledgments improvements. Clin Chem Lab Med. 2020;58(4):460–70. No external support has been received. Publisher’s Note Authors’ contributions Springer Nature remains neutral with regard to jurisdictional claims in pub‑ All the authors carried out assistance and research work associated with the lished maps and institutional affiliations. Vall d’Hebron Campus. ** Ruiz-Rodríguez JC MD, PhD: constructing an idea or hypothesis for manuscript, planning methodology, organising the course of the Project, taking responsibility in data management and reporting, taking responsibility in logical interpretation and presentation of the results, literature review, reviewing the article before submission for its intellectual content, writer. ** Chiscano-Camón L MD: planning methodology, organising the course of the Project, taking responsibility in data management and reporting, taking responsibility in logical interpretation and presentation of the results, literature review, writer. ** Roser Ferrer MD, PhD: literature review, reviewing the article before submission for its intellectual content, writer. ** Silvia Camos MD: literature review, reviewing the article before submission for its intellec‑ tual content, writer. ** Adolf Ruiz-Sanmartin MD: literature review, reviewing the article before submission for its intellectual content. **Ricard Ferrer MD, PhD: reviewing the article before submission for its intellectual content. The authors read and approved the final manuscript. Funding This research received no external funding. Availability of data and materials The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request. Declarations Ethics approval and consent to participate Not applicable, as we made no intervention but only analytic measurement. Moreover, the study was approved by the local Clinical Research Ethics Com‑ mittee (PR(AG)270/2020) with exemption from informed consent. Ready to submit your research ? Choose BMC and benefit from: Consent for publication Not applicable. • fast, convenient online submission Competing interests • thorough peer review by experienced researchers in your field The authors declare that they have no competing interests. • rapid publication on acceptance • support for research data, including large and complex data types Author details 1 • gold Open Access which fosters wider collaboration and increased citations Intensive Care Department, Vall d’Hebron Hospital Universitari, Vall d’Hebron Barcelona Hospital Campus, Barcelona, Spain. 2 Shock, Organ Dysfunction • maximum visibility for your research: over 100M website views per year and Resuscitation Research Group, Vall d’Hebron Institut de Recerca (VHIR), Vall d’Hebron Hospital Universitari, Vall d’Hebron Barcelona Hospital Campus, At BMC, research is always in progress. Barcelona, Spain. 3 Departament de Medicina, Universitat Autònoma de Barcelona, Bellaterra, Spain. 4 Biochemistry Department, Clinical Laboratories, Learn more biomedcentral.com/submissions