Editor: Deborah Sesok-Pizzini, MD, MBA, chief medical officer, Labcorp Diagnostics, Burlington, NC, and adjunct professor, Department of Clinical Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia.
Use of electrophoresis and HPLC to estimate voxelotor concentration in sickle cell disease
July 2024—People with sickle cell disease may undergo treatment with the medication voxelotor, which can increase hemoglobin levels and help reduce hemolysis. A clinician treating a sickle cell disease patient with voxelotor may want to know the whole blood concentration of the drug to better monitor the patient’s treatment response, inform therapy, or confirm the patient is complying with the directions for use of the drug. Voxelotor binds to the alpha subunit of hemoglobin and results in the hemoglobin molecule being more likely to stay in the oxygenated conformation. In vivo concentrations of voxelotor cannot be measured in most clinical settings. However, voxelotor has been found to cause peak splitting in common forms of hemoglobin measurement, such as capillary zone electrophoresis (CZE) and high-performance liquid chromatography (HPLC)1—that is, the classic peaks for each hemoglobin species split into a peak that has bound drug and a peak that does not. Liquid chromatography-tandem mass spectrometry (LC-MS/MS), which is only available in select laboratories, can be used to measure voxelotor concentrations. The authors hypothesized that the degree of splitting observed on CZE and HPLC may correlate with voxelotor whole blood concentration or the percentage of total hemoglobin bound with the drug. Furthermore, having a method available in the clinical setting to measure the concentration of voxelotor could help clinicians optimize use of the drug. The authors conducted a study to test their hypothesis, in which they took blood from sickle cell disease patients dosed with known concentrations of voxelotor and performed a multiparameter regression to derive an equation to define the concentration of voxelotor and the degree of peak splitting observed. They validated the equation using 21 patients started on 1,500 mg/day of voxelotor who had blood samples drawn at days zero, 14, 30, and 60. Samples were then sent out for gold standard testing using LC-MS/MS. The derived equation was used to calculate voxelotor concentrations for the study. The results showed that the calculated concentrations correlated strongly with measured concentrations for the CZE and HPLC methodologies. The authors also demonstrated that higher whole blood concentrations of voxelotor correlated with higher increases in hemoglobin (R2=0.40, P<.001). Of interest, the authors examined the correlation of whole blood concentrations to hematologic response and found that 38 percent of the response could be explained by voxelotor concentrations. Many factors likely determine whether a person will have a hematologic response to voxelotor since blood levels alone could not account for the variation in patient response. The authors emphasized that this study used a single CZE and HPLC instrument, so their equation may not be applicable to all sites. Institutional validation of the equation is needed. However, the authors demonstrated that the degree of peak splitting by voxelotor in CZE and HPLC studies of people with sickle cell disease can be used to estimate the whole blood concentration of the drug, which may be clinically useful.
1. Rutherford NJ, Thoren KL, Shanjani-Yi Z, et al. Voxelotor (GBT440) produces interferences in measurements of hemoglobin S. Clin Chim Acta. 2018;482:57–59.
Curtis SA, Friedman E, Minniti C, et al. Concentration of voxelotor in sickle cell disease can be estimated using electrophoresis and high-performance liquid chromatography. Am J Clin Pathol. 2024. doi:10.1093/AJCP/AQAE042
Correspondence: Dr. Susanna Curtis at susanna.curtis@mssm.edu
Outcomes in transfusion recipients before and after blood donor SARS-CoV-2 infection and vaccination
Numerous randomized clinical trials have investigated the safety and efficacy of COVID-19 convalescent plasma for preventing more severe COVID-19 outcomes. Some adverse outcomes from these transfusions are thought to be due to autoantibodies in units of COVID-19 convalescent plasma (CCP). Although the transfusion of CCP to COVID-19 patients has been studied extensively, data on the safety of transfusing these products to people who do not have COVID-19 are not available. The prevalence of SARS-CoV-2 antibodies in U.S. blood donors increased from 11 to 70 percent from December 2020 to September 2022. This may include a rise in autoantibodies that were previously associated with adverse events in COVID-19 patients. Patient advocacy groups and lawmakers have raised concerns about SARS-CoV-2 antibodies and autoantibodies transfused in high plasma volume blood products, including platelets. The authors conducted a study to assess whether transfusion of plasma or plasma-rich platelet products collected during periods of increased SARS-CoV-2 infection and vaccination were associated with changes in rates of adverse events, including thrombosis, pulmonary events, ICU length of stay, hospital mortality, and rehospitalization, in transfusion recipients who were not experiencing COVID-19. The retrospective cohort study focused on hospitalized adults at Kaiser Permanente Northern California who received plasma or platelet transfusions at any of Kaiser’s 21 hospitals between March 1, 2018 and Aug. 31, 2022. Data were divided into three study periods: before COVID-19 (March 2018 through February 2020), before the COVID-19 vaccine (March 2020 through February 2021), and after the COVID-19 vaccine (March 2021 through August 2022). Transfusion recipients were grouped based on receiving only plasma blood components, only platelet components, or both plasma and platelet components. Patients who received a transfusion during more than one hospital stay were included in the study, while patients with a positive SARS-CoV-2 test by nasal swab polymerase chain reaction within 90 days of hospitalization were excluded. The authors analyzed the study results using multivariable logistic regression analysis with generalized estimating equations to adjust for demographics and comorbidities. They then calculated odds ratios. Statistical significance was indicated by the 95 percent confidence interval or two-sided P values of less than .05. From 2018 to 2022, Kaiser had 21,750 hospitalizations involving 18,584 recipients of plasma or platelet products. After excluding 5,891 hospitalizations in which there was a history of thrombosis or patients started on anticoagulants before transfusion, the authors noted 697 (4.4 percent) post-transfusion thrombotic events. Furthermore, after excluding 4,701 hospitalizations in which patients had increased oxygen requirements before transfusion, the authors reported that oxygen requirements increased in 1,751 (10.3 percent) hospitalizations during the 24- to 48-hour period after transfusion. In multivariable analyses comparing the pre-COVID, pre-vaccine, and post-vaccine study periods, there were no trends in rates of thromboses (odds ratio, 0.9, P=.22) or oxygen requirements (odds ratio, 1.0, P=.41). In addition, no trends across study periods were found for adjusted hospital mortality for all subsets of recipients of plasma products and among unvaccinated recipients. Nor were trends found in rates of 30-day rehospitalization (P=.29) across study periods for all transfused recipients and ICU length of stay (P=.83). The authors concluded that transfusing plasma and platelet blood components collected during the pre- and post-vaccine periods of the COVID-19 pandemic was not associated with increased adverse outcomes in patients who did not have COVID-19. They noted that these findings should be reassuring for clinicians and blood banking professionals and should
not change donor and transfusion practices.
Roubinian NH, Greene J, Liu VX, et al. Clinical outcomes in hospitalized plasma and platelet transfusion recipients prior to and following widespread blood donor SARS-CoV-2 infection and vaccination. Transfusion. 2024;64:53–67.
Correspondence: Dr. Nareg H. Roubinian at nareg.h.roubinian@kp.org