Complement C5 inhibition protects against hemolytic anemia and acute kidney injury in anthrax peptidoglycan-induced sepsis in baboons.

Late-stage anthrax infections are characterized by dysregulated immune responses and hematogenous spread of Bacillus anthracis, leading to extreme bacteremia, sepsis, multiple organ failure, and, ultimately, death. Despite the bacterium being nonhemolytic, some fulminant anthrax patients develop a secondary atypical hemolytic uremic syndrome (aHUS) through unknown mechanisms. We recapitulated the pathology in baboons challenged with cell wall peptidoglycan (PGN), a polymeric, pathogen-associated molecular pattern responsible for the hemostatic dysregulation in anthrax sepsis. Similar to aHUS anthrax patients, PGN induces an initial hematocrit elevation followed by progressive hemolytic anemia and associated renal failure. Etiologically, PGN induces erythrolysis through direct excessive activation of all three complement pathways. Blunting terminal complement activation with a C5 neutralizing peptide prevented the progressive deposition of membrane attack complexes on red blood cells (RBC) and subsequent intravascular hemolysis, heme cytotoxicity, and acute kidney injury. Importantly, C5 neutralization did not prevent immune recognition of PGN and shifted the systemic inflammatory responses, consistent with improved survival in sepsis. Whereas PGN-induced hemostatic dysregulation was unchanged, C5 inhibition augmented fibrinolysis and improved the thromboischemic resolution. Overall, our study identifies PGN-driven complement activation as the pathologic mechanism underlying hemolytic anemia in anthrax and likely other gram-positive infections in which PGN is abundantly represented. Neutralization of terminal complement reactions reduces the hemolytic uremic pathology induced by PGN and could alleviate heme cytotoxicity and its associated kidney failure in gram-positive infections.

Inhibition of complement C1s improves severe hemolytic anemia in cold agglutinin disease: a first-in-human trial.

Cold agglutinin disease is a difficult-to-treat autoimmune hemolytic anemia in which immunoglobulin M antibodies bind to erythrocytes and fix complement, resulting in predominantly extravascular hemolysis. This trial tested the hypothesis that the anti-C1s antibody sutimlimab would ameliorate hemolytic anemia. Ten patients with cold agglutinin disease participated in the phase 1b component of a first-in-human trial. Patients received a test dose of 10-mg/kg sutimlimab followed by a full dose of 60 mg/kg 1 to 4 days later and 3 additional weekly doses of 60 mg/kg. All infusions were well tolerated without premedication. No drug-related serious adverse events were observed. Seven of 10 patients with cold agglutinin disease responded with a hemoglobin increase >2 g/dL. Sutimlimab rapidly increased hemoglobin levels by a median of 1.6 g/dL within the first week, and by a median of 3.9 g/dL (interquartile range, 1.3-4.5 g/dL; 95% confidence interval, 2.1-4.5) within 6 weeks (P = .005). Sutimlimab rapidly abrogated extravascular hemolysis, normalizing bilirubin levels within 24 hours in most patients and normalizing haptoglobin levels in 4 patients within 1 week. Hemolytic anemia recurred when drug levels were cleared from the circulation 3 to 4 weeks after the last dose of sutimlimab. Reexposure to sutimlimab in a named patient program recapitulated the control of hemolytic anemia. All 6 previously transfused patients became transfusion-free during treatment. Sutimlimab was safe, well tolerated, and rapidly stopped C1s complement-mediated hemolysis in patients with cold agglutinin disease, significantly increasing hemoglobin levels and precluding the need for transfusions. This trial was registered at www.clinicaltrials.gov as #NCT02502903.

Anti-A/B isoagglutinin reduction in an intravenous immunoglobulin product and risk of hemolytic anemia: a hospital-based cohort study.

BACKGROUND: Intravenous immunoglobulins (IVIG) are derived from large human plasma pools. IVIG-associated hemolytic anemia (HA) is a known class effect, likely attributed to dose-dependent passive transfer of anti-A/B isoagglutinins. Two isoagglutinin reduction steps were implemented in the manufacturing process of Privigen (human 10% liquid IVIG): exclusion of high-anti-A-titer donors in 2013, replaced by specific immunoaffinity chromatography in 2015. We aim to estimate the clinical effectiveness of both measures. STUDY DESIGN AND METHODS: Using the US hospital-based Premier Healthcare Database, three Privigen cohorts were generated based on calendar periods indicative of manufacturing changes: Period 1 (baseline) January 2008 to December 2012, Period 2 (high-anti-A-titer donor exclusion) October 2013 to December 2015, and Period 3 (immunoaffinity chromatography) October 2016 to April 2019. HA within a 10-day at-risk period after Privigen administrations was identified from review of patient record summaries. Incidence rate ratios (IRRs) were estimated from Poisson regression (Period 1 reference) adjusting for hospital setting, sex, age, Privigen indication, dose, and first use. RESULTS: Crude incidence rates of HA were 1.49 per 10,000 person-days in Period 1 (38 HA, 9439 patients), 1.01 in Period 2 (20 HA, 7710 patients), and 0.14 in Period 3 (3 HA, 7759 patients). Adjusted IRR for HA in Period 2 was 0.71 (95% confidence interval [CI], 0.41-1.23), and in Period 3 was 0.10 (0.03-0.33) compared with Period 1. The IRR for HA in Period 3 compared with Period 2 was 0.14 (95% CI, 0.04-0.47). CONCLUSION: Implementation of immunoaffinity chromatography in Privigen manufacturing resulted in a significant 90% reduction of HA risk. HA has become a rare event in association with Privigen use.

Delayed haemolysis after treatment with intravenous artesunate in patients with severe malaria in India.

BACKGROUND: Parenteral artesunate is the treatment of choice for severe malaria. It is safe, efficacious and well tolerated anti-malarial. However, delayed haemolysis has been reported in travellers, non-immune individuals and in African children. METHODS: A prospective, observational study was carried out in admitted severe malaria patients receiving parenteral artesunate. The patients were followed up until day 28 for monitoring clinical as well as laboratory parameters for haemolytic anaemia. RESULTS: Twenty-four patients with severe malaria receiving injection artesunate were enrolled in the study. Post-artesunate delayed haemolysis following parenteral artesunate therapy was observed in three of 24 patients (12.5%, 95% confidence interval 4.5-31.2%). Haemolysis was observed in two more patients possibly due to other reasons. The haemoglobin fall ranged from 13.6 to 38.3% from day 7 to day 28 in these patients. CONCLUSION: The possibility of delayed haemolysis should be considered while treating the severe malaria patients with parenteral artesunate. The study highlights the need for further studies in different epidemiological settings.

C3 inhibition with pegcetacoplan in subjects with paroxysmal nocturnal hemoglobinuria treated with eculizumab.

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired, life-threatening hematologic disease characterized by chronic complement-mediated hemolysis and thrombosis. Despite treatment with eculizumab, a C5 inhibitor, 72% of individuals remain anemic. Pegcetacoplan (APL-2), a PEGylated C3 inhibitor, has the potential to provide more complete hemolysis control in patients with PNH. This open-label, phase Ib study was designed to assess the safety, tolerability, and pharmacokinetics of pegcetacoplan in subjects with PNH who remained anemic during treatment with eculizumab. Pharmacodynamic endpoints were also assessed as an exploratory objective of this study. Data are presented for six subjects in cohort 4 who received treatment for up to 2 years. In total, 427 treatment-emergent adverse events (TEAEs) were reported, 68 of which were possibly related to the study drug. Eight serious TEAEs occurred in two subjects; three of these events were considered possibly related to the study drug. Pegcetacoplan pharmacokinetic concentrations accumulated with repeated dosing, and steady state was reached at approximately 6-8 weeks. Lactate dehydrogenase levels were well controlled by eculizumab at baseline. Pegcetacoplan increased hemoglobin levels and decreased both reticulocyte count and total bilirubin in all six subjects. Improvements were observed in Functional Assessment of Chronic Illness Therapy Fatigue scores. Two subjects discontinued for reasons unrelated to pegcetacoplan. All four subjects who completed the study transitioned to pegcetacoplan monotherapy following eculizumab discontinuation and avoided transfusions. In this small study, pegcetacoplan therapy was generally well-tolerated, and resulted in an improved hematological response by achieving broad hemolysis control, enabling eculizumab discontinuation.

Postponing Early intrauterine Transfusion with Intravenous immunoglobulin Treatment; the PETIT study on severe hemolytic disease of the fetus and newborn.

BACKGROUND: Intrauterine transfusion for severe alloimmunization in pregnancy performed <20 weeks' gestation is associated with a higher fetal death rate. Intravenous immunoglobulins may prevent hemolysis and could therefore be a noninvasive alternative for early transfusions. OBJECTIVE: We evaluated whether maternal treatment with intravenous immunoglobulins defers the development of severe fetal anemia and its consequences in a retrospective cohort to which 12 fetal therapy centers contributed. STUDY DESIGN: We included consecutive pregnancies of alloimmunized women with a history of severe hemolytic disease and by propensity analysis compared index pregnancies treated with intravenous immunoglobulins (n = 24) with pregnancies managed without intravenous immunoglobulins (n = 28). RESULTS: In index pregnancies with intravenous immunoglobulin treatment, fetal anemia developed on average 15 days later compared to previous pregnancies (8% less often <20 weeks' gestation). In pregnancies without intravenous immunoglobulin treatment anemia developed 9 days earlier compared to previous pregnancies (10% more <20 weeks), an adjusted 4-day between-group difference in favor of the immunoglobulin group (95% confidence interval, -10 to +18; P = .564). In the subcohort in which immunoglobulin treatment was started <13 weeks, anemia developed 25 days later and 31% less <20 weeks' gestation (54% compared to 23%) than in the previous pregnancy. Fetal hydrops occurred in 4% of immunoglobulin-treated pregnancies and in 24% of those without intravenous immunoglobulin treatment (odds ratio, 0.03; 95% confidence interval, 0-0.5; P = .011). Exchange transfusions were given to 9% of neonates born from pregnancies with and in 37% without immunoglobulin treatment (odds ratio, 0.1; 95% confidence interval, 0-0.5; P = .009). CONCLUSION: Intravenous immunoglobulin treatment in mothers pregnant with a fetus at risk for hemolytic disease seems to have a potential clinically relevant, beneficial effect on the course and severity of the disease. Confirmation in a multicenter randomized trial is needed.

Treatment of Congenital Thrombotic Thrombocytopenia Purpura: A New Paradigm.

Congenital thrombotic thrombocytopenia purpura (cTTP) is a very rare disorder worldwide. Standard treatment of recognized cases has been to administer fresh frozen plasma as the source of ADAMTS13, to replenish the absent ADAMTS13 enzyme. An alternative source, a plasma-derived factor VIII concentrate used for hemophilia A, and found to contain this enzyme, was reported to be effective in 1 patient in the United States. We now report details on a US cohort of 8 cTTP patients who have been successfully treated for varying periods with a marketed antihemophilic factor concentrate Koate-DVI. This biological product has been used successfully on demand in varying doses to treat acute exacerbations, as well as prophylactically (3 to 6 U ADAMTS13 every 3 to 21 d). Self-infused at home, in lieu of fresh frozen plasma therapy in the hospital setting, this product has effectively prevented episodes of thrombocytopenia, microangiopathic hemolytic anemia, and the concomitant organ damage in these patients. This specific virus inactivated product can be used to prevent further manifestations of this congenital enzyme deficiency.

Potential for Recombinant ADAMTS13 as an Effective Therapy for Acquired Thrombotic Thrombocytopenic Purpura.

OBJECTIVE: The metalloprotease ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) regulates the size of von Willebrand factor multimers. A deficiency in ADAMTS13 activity is associated with the life-threatening disease thrombotic thrombocytopenic purpura (TTP). The vast majority of patients have acquired TTP, where circulating anti-ADAMTS13 autoantibodies are causative for the decreased ADAMTS13 activity. Current treatment consists of plasma exchange, but improved therapies are highly warranted. APPROACH AND RESULTS: We have developed a new rat model mimicking various aspects of acquired TTP to investigate the therapeutic efficacy of human recombinant ADAMTS13. A polyclonal antibody against ADAMTS13 completely blocked endogenous rat ADAMTS13 activity in Sprague-Dawley rats. When TTP was triggered using recombinant von Willebrand factor, the animals displayed severe TTP-like symptoms, such as thrombocytopenia, hemolytic anemia, and von Willebrand factor-rich thrombi in the kidneys and brain. Subsequent injection of 400, 800, or 1600 U/kg recombinant ADAMTS13 prevented full development of these symptoms. Analysis of plasma samples confirmed that recombinant ADAMTS13 was able to override circulating anti-ADAMTS13 inhibitory antibodies, resulting in restoration of ADAMTS13 activity and degradation of ultralarge von Willebrand factor multimers. CONCLUSIONS: Recombinant ADAMTS13 was shown to be effective in averting severe acquired TTP-like symptoms in rats and holds promising value for the treatment of this severe and life-threatening disease in humans.

Use of cffDNA to avoid administration of anti-D to pregnant women when the fetus is RhD-negative: implementation in the NHS.

OBJECTIVE: To determine whether a policy of offering cffDNA testing to all RhD-negative women at about 16 weeks' gestation to avoid anti-D administration when the fetus is RhD-negative could be implemented successfully in the NHS without additional funding. DESIGN: Prospectively planned observational service implementation pilot and notes audit. SETTING: Three maternity services in the South West of England. POPULATION: All RhD-negative women in a 6-month period. METHODS: Prospective, intervention, cross-sectional observational study, using pre-intervention data as controls. MAIN OUTCOME MEASURES: Proportion of suitable women who offered and accepted the test. Accuracy of the cffDNA result as assessed by cord blood group result. Fall in anti-D doses administered. RESULTS: 529 samples were received; three were unsuitable. The results were reported as RhD-positive (n = 278), RhD-negative (n = 185) or inconclusive, treat as positive (n = 63). Cord blood results were available in 502 (95%) and the only incorrect result was one case of a false positive (cffDNA reported as positive, cord blood negative - and so given anti-D unnecessarily). The notes audit showed that women who declined this service were correctly managed and that anti-D was not given when the fetus was predicted to be RhD-negative. The total use of anti-D doses fell by about 29% which equated to about 35% of RhD-negative women not receiving anti-D in their pregnancy unnecessarily. CONCLUSIONS: We recommend this service is extended to all UK NHS services.

ROCK1 functions as a critical regulator of stress erythropoiesis and survival by regulating p53.

Erythropoiesis is a dynamic, multistep process whereby hematopoietic stem cells differentiate toward a progressively committed erythroid lineage through intermediate progenitors. Although several downstream signaling molecules have been identified that regulate steady-state erythropoiesis, the major regulators under conditions of stress remain poorly defined. Rho kinases (ROCKs) belong to a family of serine/threonine kinases. Using gene-targeted ROCK1-deficient mice, we show that lack of ROCK1 in phenylhydrazine-induced oxidative stress model results in enhanced recovery from hemolytic anemia as well as enhanced splenic stress erythropoiesis compared with control mice. Deficiency of ROCK1 also results in enhanced survival, whereas wild-type mice die rapidly in response to stress. Enhanced survivability of ROCK1-deficient mice is associated with reduced level of reactive oxygen species. BM transplantation studies revealed that enhanced stress erythropoiesis in ROCK1-deficient mice is stem cell autonomous. We show that ROCK1 binds to p53 and regulates its stability and expression. In the absence of ROCK1, p53 phosphorylation and expression is significantly reduced. Our findings reveal that ROCK1 functions as a physiologic regulator of p53 under conditions of erythroid stress. These findings are expected to offer new perspectives on stress erythropoiesis and may provide a potential therapeutic target in human disease characterized by anemia.

Cost-effectiveness of prospective red blood cell antigen matching to prevent alloimmunization among sickle cell patients.

BACKGROUND: Sickle cell disease is associated with extensive health care utilization; estimated lifetime costs exceed $460,000 per patient. Approximately 30% of chronically transfused sickle cell patients become alloimmunized to red blood cell antigens, but these patients cannot be identified a priori. Prospective antigen matching can prevent alloimmunization, but is costly and may not benefit most patients. STUDY DESIGN AND METHODS: A Markov-based model was constructed to compare the health and financial implications of four alternative antigen-matching strategies for chronically transfused sickle cell patients. The strategies varied by the group of patients receiving matched blood (all patients prophylactically or only patients with a history of alloimmunization [history-based]), and by the extent of antigen matching (limited to C, E, and K, or extended to 11 antigens). Direct medical costs and alloimmunization events were assessed over 10- and 20-year periods, for a hypothetical cohort of initially transfusion-naive patients and for a dynamic population. RESULTS: Within a hypothetical cohort of initially transfusion-naive patients, implementing prophylactic limited matching for all chronically transfused patients instead of history-based limited matching is expected to cost an additional $765.56 million over 10 years, but result in 2072 fewer alloimmunization events. Within the same cohort, implementing prospective extensive matching is expected to cost $1.86 billion more than history-based extensive matching, but result in 2424 fewer alloimmunization events. Averting a single alloimmunization event using prospective matching would cost $369,482 to $769,284. Among a dynamic population over 10 years, prospective limited matching is expected to cost $358.34 million more than history-based limited matching. CONCLUSIONS: While prospective matching for all transfused patients would reduce alloimmunization, this strategy requires considerable expenditure.

Therapeutic plasma exchange and intravenous immunoglobulin as primary therapy for D alloimmunization in pregnancy precludes the need for intrauterine transfusion.

BACKGROUND: Maternal D alloimmunization detected in early gestation requires aggressive intervention to prevent severe fetal anemia. An intrauterine transfusion (IUT) is indicated to prevent fetal death once severe fetal anemia has been detected, but is not without risk. Protocols combining therapeutic plasma exchange (TPE) and intravenous immunoglobulin (IVIG) have been described, but they usually bridge to IUT. STUDY DESIGN AND METHODS: We describe a 27-year-old G4, P0-1-2-0 Caucasian female with a history of ruptured ectopic pregnancy presented at 12 weeks' gestation with a very high anti-D titer (2048). TPE was performed on that week and twice more in the following week, with a fourth final exchange during Week 14. A loading dose of IVIG (2 g/kg) was administered over 2 days after the third TPE and then 1 g/kg per week until Week 28 (total, 14 doses). RESULTS: The antibody titer decreased to 256 by the beginning of 15 weeks' gestation and remained stable at that level for the remainder of the pregnancy. Doppler ultrasonographic measurements of the fetal middle cerebral artery peak flow velocity performed throughout gestation showed no evidence of fetal anemia. A healthy male infant was delivered at 37 weeks' gestation with mild immune-mediated hemolysis. The infant underwent successful treatment with an IVIG dose of 750 mg/kg and a red blood cell exchange. CONCLUSION: Our unique TPE-IVIG protocol was successful at preventing the onset of severe fetal anemia in a patient with high titer anti-D. Since IUT may be fatal, our approach offers a safer and less-invasive treatment regime that can adequately sustain a fetus until term.

Mass primaquine treatment to eliminate vivax malaria: lessons from the past.

Recent successes in malaria control have put malaria eradication back on the public health agenda. A significant obstacle to malaria elimination in Asia is the large burden of Plasmodium vivax, which is more difficult to eliminate than Plasmodium falciparum. Persistent P. vivax liver stages can be eliminated only by radical treatment with a ≥ seven-day course of an 8-aminoquinoline, with the attendant risk of acute haemolytic anaemia in individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency. Primaquine is the only generally available 8-aminoquinoline. Testing for G6PD deficiency is not widely available, and so whilst it is widely recommended, primaquine is often not prescribed. In the past, some countries aiming for vivax malaria eradication deployed mass treatments with primaquine on a massive scale, without G6PD testing. In Azerbaijan, Tajikistan (formerly USSR), North Afghanistan and DPR Korea 8,270,185 people received either a 14-day "standard" or a 17-day "interrupted" primaquine treatment to control post-eradication malaria epidemics. These mass primaquine preventive treatment campaigns were conducted by dedicated teams who administered the drugs under supervision and then monitored the population for adverse events. Despite estimated G6PD prevalences up to 38.7%, the reported frequency of severe adverse events related to primaquine was very low. This experience shows that with careful planning and implementation of mass treatment strategies using primaquine and adequate medical support to manage haemolytic toxicity, it is possible to achieve high population coverage, substantially reduce malaria transmission, and manage the risk of severe acute haemolytic anaemia in communities with a relatively high prevalence of G6PD deficiency safely.

Routine administration of Anti-D: the ethical case for offering pregnant women fetal RHD genotyping and a review of policy and practice.

BACKGROUND: Since its introduction in the 1960s Anti-D immunoglobulin (Anti-D Ig) has been highly successful in reducing the incidence of haemolytic disease of the fetus and newborn (HDFN) and achieving improvements to maternal and fetal health. It has protected women from other invasive interventions during pregnancy and prevented deaths and damage amongst newborns and is a technology which has been adopted worldwide. Currently about one third of pregnant women with the blood group Rhesus D (RhD) negative in the UK (approximately 40,000 women per year in England and Wales), receive antenatal Anti-D Ig in pregnancy when they do not require it because they are carrying a RhD negative fetus. Since 1997, a test using cell free fetal DNA (cffDNA) in maternal blood has been developed to identify the genotype of the fetus and can be used to predict the fetal RhD blood group. DISCUSSION: This paper considers whether it is ethically acceptable to continue administering antenatal Anti-D Ig to all RhD negative women when fetal RHD genotyping using maternal blood could identify those women who do not need this product. SUMMARY: The antenatal administration of Anti-D Ig to a third of RhD negative pregnant women who carry a RhD negative fetus and therefore do not need it raises important ethical issues. If fetal RHD genotyping using maternal blood was offered to all RhD negative pregnant women it would assist them to make an informed choice about whether or not to have antenatal Anti-D Ig.

Using nitrofurantoin while breastfeeding a newborn.

QUESTION: My patient has a urinary tract infection and is currently breastfeeding. Her son is only 3 weeks old. Is nitrofurantoin a safe antibiotic for treatment? ANSWER: The use of nitrofurantoin in breastfeeding mothers is generally safe, as only small amounts transfer into the breast milk. Despite the lack of documented reports, there is a risk of hemolytic anemia in all newborns exposed to nitrofurantoin owing to their glutathione instability, especially in infants with glucose-6-phosphate dehydrogenase deficiency. Although some suggest that nitrofurantoin be avoided in infants younger than 1 month, studies have noted that glutathione stability might be established by the eighth day of life. In infants younger than 1 month, an alternative antibiotic might be preferred; however, if an alternative were not available, the use of nitrofurantoin would not be a reason to avoid breastfeeding. In any such case the suckling infant should be monitored by his or her physician.

Antenatal immunoglobulin for fetal red blood cell alloimmunization.

BACKGROUND: Red blood cell alloimmunization in pregnancy can lead to fetal anaemia with potentially disastrous consequences. Traditional management involves the use of intrauterine transfusion, which is associated with significant procedure-related risks. An alternative treatment that has been trialled is the use of immunoglobulin administered intravenously to the mother. OBJECTIVES: The objective of this review was to assess the efficacy and safety of the use of intravenous immunoglobulin antenatally to women with severe fetal red blood cell alloimmunization. SEARCH METHODS: We searched the Cochrane Pregnancy and Childbirth Group trials register (19 December 2012), and reference lists of articles. SELECTION CRITERIA: Randomized trials assessing the antenatal use of intravenous immunoglobulin administered at any dose, frequency or duration with a control group (using any other, or no treatment) in the management of fetal red blood cell alloimmunization. DATA COLLECTION AND ANALYSIS: Two review authors independently assessed the available evidence. MAIN RESULTS: There are no included studies. AUTHORS' CONCLUSIONS: No information is available from randomized trials to indicate whether the antenatal use of intravenous immunoglobulin is effective in the management of fetal red blood cell alloimmunization. Several case series suggest a beneficial role in delaying the onset of fetal anaemia requiring invasive intrauterine transfusion.

ABO antibody titers are not predictive of hemolytic reactions due to plasma-incompatible platelet transfusions.

BACKGROUND: The overall risk of hemolytic transfusion reactions (HTRs) from plasma (minor)-incompatible platelet (PLT) transfusions and the role of a critical anti-A or anti-B titer in predicting and preventing these reactions has not been clearly established. STUDY DESIGN AND METHODS: We evaluated all apheresis PLT (AP) transfusions for 3 months. Using the gel titer method, we determined the anti-A and/or the anti-B immunoglobulin (Ig)G titer for all incompatible APs. Reported febrile transfusion reactions and HTRs were recorded; transfusions were not prospectively evaluated by the study team. A posttransfusion direct antiglobulin test (DAT) and eluate were performed after a reported febrile or hemolytic reaction for patients who received plasma-incompatible APs. RESULTS: A total of 647 of 4288 AP transfusions (15.1%) were plasma incompatible. Group O APs (n = 278) had significantly higher anti-A and anti-B titers than group A or B APs (p < 0.0001). No group A or B APs had a titer of more than 128 (0/342). For group O APs, 73 had titers of 256 or greater (26.3%), and 27 had titers of 512 or greater (9.7%). No HTRs were reported to any plasma-incompatible AP transfusion during the study period. Two plasma-incompatible AP transfusions were associated with fever and chills and positive DATs, of which one had a positive eluate. The incidence of a DAT and eluate-positive febrile transfusion reaction in the plasma-incompatible AP population is 0.15% (95% confidence interval, 0.0%-0.86%). CONCLUSION: A critical anti-A or -B titer is not sufficient to predict the risk of hemolysis in patients receiving plasma-incompatible APs, although underreporting of reactions to the blood bank may limit the generalizability of this study.