We read with interest the recent paper by Lin and colleagues (1) and while we commend them on their care of a critically ill patient, we have concerns regarding the interpretation of their plasma exchange data. While many of the critical parameters needed to evaluate the efficacy of plasma exchange (PE), such as patient weight, are omitted or not explicitly stated in the report,(2) enough data are available to provide an approximation. Using a “best-case” estimate of the volume of distribution of thallium at 3L/kg and an assumed patient weight of 50kg we can deduce the following:
● Blood [thallium] at the first PE (on figure 1) = 280ng/mL = 280mcg/L
● Total body content of thallium at the time of the 1st PE: 50kg x 3L/kg x 280mcg/L = 42,000 mcg = 42mg
● [Thallium] in effluent at the 1st PE (on figure 1) = 120ng/mL = 120mcg/L
● Effluent volume during the 1st PE (as stated in the supplemental material) = 1.95L
● Amount of thallium removed by the 1st PE = 1.95L x 120mcg/L = 234mcg = 0.234mg
● Percentage of thallium removed during 1st exchange = 0.234mg/42mg = 0.55%
According to EXTRIP’s criteria for “dialyzability”, these results are considered “non-dialyzable”.(3) Given these data, we conclude that plasma exchange was inconsequential. The interpretation of a decreasing blood thallium concentration as evidence of the efficacy of plasma exchange is misleading due to the large volume of distribution of thallium, and the cumulative effects of endogenous clearance and to prussian blue. As noted by the authors the benefit of plasma exchange is most evident for toxins that are highly protein bound and thallium has no protein binding.(4) While we agree that the precise role of intermittent hemodialysis and hemoperfusion is not entirely determined in patients with thallium poisoning (5) we argue that this report speaks strongly against the use of plasma exchange. Intermittent hemodialysis in this case might have removed more thallium, at lower cost, and risk to the patient.
Robert S. Hoffman, MD, Division of Medical Toxicology, NYU School of Medicine, USA
Marc Ghannoum, MD FRCP, Department of Medicine University of Montreal, Verdun Hospital, Canada
Sophie Gosselin, MD FRCP, Emergency Department Hôpital Charles-Lemoyne, Canada
 Lin G, Yuan L, Bai L, Liu Y, Wang Y, Qiu Z. Successful treatment of a patient with severe thallium poisoning in a coma using Prussian blue and plasma exchange: A case report. Medicine (Baltimore). 2019;98(8):e14629.
 Lavergne V, Ouellet G, Bouchard J, et al. Guidelines for reporting case studies on extracorporeal treatments in poisonings: methodology. Semin Dial. 2014;27(4):407-414.
 Lavergne V, Nolin TD, Hoffman RS, et al. The EXTRIP (EXtracorporeal TReatments In Poisoning) workgroup: guideline methodology. Clin Toxicol (Phila). 2012;50(5):403-413.
 Ghannoum M, Hoffman RS, Gosselin S, Nolin TD, Lavergne V, Roberts DM. Use of
extracorporeal treatments in the management of poisonings. Kidney Int. 2018;94(4):682-688.
 Ghannoum M, Nolin TD, Goldfarb DS, et al. Extracorporeal Treatments in Poisoning Workgroup. Extracorporeal treatment for thallium poisoning: recommendations from the EXTRIP Workgroup. Clin J Am Soc Nephrol. 2012;7(10):1682-1690.