Dear Editor,

I read with interest the review article of Brown et al. on COVID-19 treatment using convalescent plasma \[[@bib0005]\]. The review highlighted three case series from China, which cumulatively enrolled 19 patients. The case series were two studies on critically ill (the first and third study), and one study on severely ill patients (the second study). However, the information in the text and Table was inconsistent and confusing. The reference numbers in the text are different from those in the Table. From the Table, there were three case series of five and four critically ill patients from first (ref. no 14) and third (ref. no 30) studies, and ten severely ill patients from the second study (ref. no 16), while in the text it was stated: "There have been 3 case series from China for the use of convalescent plasma to treat COVID-19 (19 total patients)" (reference number 16, 26, 27). Moreover, there is a confusing statement without a reference: "In this pilot study, **9** patients received 1 dose of 200 mL convalescent plasma with neutralizing antibody titers of \> 1:640. The median time from onset of illness to convalescent plasma transfusion was 16.5 days. Within 3 days, the patients showed improved clinical symptoms along with increase of oxyhemoglobin saturation". The information of the pilot study concerning information of dose, antibody titres, median time from illness onset to convalescent plasma therapy referred to the second study on **ten** severely ill patients (ref. no 16), which was available on the Table. Therefore, there is an inconsistency in the number of patients. In addition, the time of improvement in clinical symptoms (within 3 days) referred to the first study that enrolled five patients (ref. no 14).

The results of case series showed improvement of four out of five patients in the first study, and all four patients in the third study. Though the results seemed promising \[[@bib0005]\], they need to be interpreted with caution, as they are not a robust proof compared to a randomized clinical trial. A recent systematic review on convalescent plasma for COVID-19 reviewed eight studies, which cumulatively enrolled 32 participants that consisted of seven case-series and one prospective single-arm intervention study \[[@bib0010]\]. The systematic review concluded that all outcomes were of very low certainty, as all of the outcomes could be due to other concomitant treatments or the natural course of the disease, rather than convalescent plasma \[[@bib0010]\].

Besides discussing the value of convalescence plasma in the treatment of COVID-19, the review also mentioned some considerations to be taken into account, though the case series reported no serious adverse events. The considerations to be taken into account in convalescent plasma therapy were the possibility of transfusion-related acute lung injury (TRALI), the possibility of immune (antibody dependent) enhancement (ADE) of viral pathogenicity, and safety and requirements of donor plasma \[[@bib0005],[@bib0015],[@bib0020]\]. TRALI is a risk in patients with pulmonary disease \[[@bib0005]\], while most COVID-19 patients have pulmonary involvement. However, there were some considerations that were not mentioned in the review \[[@bib0005]\]. The recent systematic review showed that one study of three participants reported one adverse event presumably grade 3 or 4, in the form of severe anaphylactic shock after convalescence plasma transfusion \[[@bib0010]\]. In addition, convalescent plasma therapy should consider the possibility of transfusion associated circulatory overload (TACO), the presence of complete immunoglobulin A deficit, which is an absolute contraindication of plasma therapy \[[@bib0015],[@bib0020]\], and the presence of cytokine storm, as plasma therapy after cytokine storm occurred is not recommended \[[@bib0020]\].
