Iron metabolism and lymphocyte characterisation during Covid-19 infection in ICU patients: an observational cohort study.

Abstract

Background: Iron metabolism and immune response to SARS-CoV-2 have not been described yet in intensive care patients, although they are likely involved in Covid-19 pathogenesis.Methods: We performed an observational study during the peak of pandemic in our intensive care unit, dosing D-dimer, C-reactive protein, Troponin T, Lactate Dehydrogenase, Ferritin, Serum iron, Transferrin, Transferrin Saturation, Transferrin Soluble Receptor, Lymphocyte count and NK, CD3, CD4, CD8, B subgroups of 31 patients during the first two weeks of their ICU stay. Correlation with mortality and severity at the time of admission was tested with Spearman coefficient and Mann-Whitney test. Trends over time were tested with Kruskall-Wallis analysis.Results: Lymphopenia is severe and constant, with a nadir on day 2 of ICU stay (median 0.555 10⁹/L; interquartile range (IQR) 0.450 10⁹/L); all lymphocytic subgroups are dramatically reduced in critically ill patients, while CD4/CD8 ratio remains normal. Neither Ferritin nor lymphocyte count follow significant trends in ICU patients. Transferrin Saturation is extremely reduced at ICU admission (median 9%; IQR 7%), then significantly increases at day 3 to 6 (median 33%, IQR 26.5%, p-value 0.026). The same trend is observed with serum iron levels (median 25.5 µg/L, IQR 69 µg/L at admission; median 73 µg/L, IQR 56 µg/L on day 3 to 6) without reaching statistical significance. Hyperferritinemia is constant during intensive care stay: however, its dosage might be helpful in individuating patients developing hemophagocytic lymphohistiocytosis. D-dimer is elevated and progressively increases from admission (median 1319 µg/L; IQR 1285 µg/L) to day 3 to 6 (median 6820 µg/L; IQR 6619 µg/L), despite not reaching significant results. We describe trends of all the above mentioned parameters during ICU stay.Conclusions: The description of iron metabolism and lymphocyte count in Covid-19 patients admitted to the Intensive Care Unit provided with this paper might allow a wider understanding of SARS-CoV-2 pathophysiology.