Pruthi, Rajiv K.

Abstract Introduction: Hemophagocytic lymphohistiocytosis (HLH) is a rare and life-threatening hyperinflammatory syndrome resulting from immune dysregulation. While diagnostic and therapeutic guidelines (e.g., HLH-2004) are established for pediatric HLH, adult-onset HLH remains both a diagnostic and therapeutic challenge, with limited characterization and sparse outcome data. Here, we conduct a single-institution retrospective cohort study to evaluate clinical features, causes, and prognostic markers associated with outcomes. Methods: We performed a retrospective chart review of all adult patients (≥18 years) first diagnosed with HLH across all Mayo Clinic sites between January 1, 2006 and July 1, 2025. Diagnosis was based on hematologist adjudication at time of care. Patients with prior diagnoses of HLH or HLH related to T-cell therapy (CAR-T) were excluded. Clinical and laboratory variables were extracted from electronic health records. The primary outcome was overall survival (OS), defined as time from diagnosis of HLH to death or last follow-up. OS was estimated using the Kaplan-Meier method. Multivariable analysis to identify independent predictors of mortality was performed using a Cox proportional hazards regression model, adjusting for age at diagnosis, sex, HLH etiology, and relevant clinical and laboratory parameters. Model discrimination was assessed using Harrell's concordance index (c-index). Descriptive statistics were summarized using median and interquartile range (IQR) for continuous variables and frequency with percentages for categorical variables. Results: A total of 203 patients diagnosed with HLH were included. The median age at diagnosis was 55 years (range 18-86). The cohort was predominantly male (n=130, 64%) and White (n=163, 80%). The majority of diagnoses occurred in more recent years, with 75 patients (36.9%) diagnosed between 2021–2025, 61 (30.0%) between 2016–2020, and 43 (21.2%) between 2011–2015. Prior to HLH diagnosis, 86 patients (42.4%) had a history of malignancy, 55 (27.1%) had a history of autoimmune disease, and 28 (13.8%) had a history of transplant. The most common HLH etiologies were malignancy-associated (n=99, 49%), infectious (n=51, 25%), and autoimmune (n=24, 12%), in addition to idiopathic (n=6, 3%), post-transplant lymphoproliferative disease or graft-vs-host disease (n=3, 1%), drug-induced (n=3, 1%), or primary HLH (n=1, 0.5%). The most common malignancies included T-cell (n=35, 17.2%) and diffuse large B-cell lymphoma (n=24, 11.8%). Forty-four cases (21.7%) were associated with Epstein-Barr virus (EBV), either through overt viremia or malignancies with EBV positivity on pathology report. Five patients (2.5%) had COVID-19–associated HLH and 2 (1.0%) were attributed to immune checkpoint inhibitors. Overall, 164 patients (80.8%) met the HLH-2004 diagnostic threshold of ≥5 out of 8 criteria, while 196 (96.6%) met the HLH-2024 ≥4 of 7 modified criteria. Among patients with available information, elevated ferritin was present in 197 of 198 (99.5%), fever in 185 of 202 (91.6%), cytopenias involving ≥2 lineages in 184 of 199 (92.5%), hemophagocytosis in 156 of 182 (85.7%), elevated sCD25 in 117 of 121 (96.7%), hypertriglyceridemia in 117 of 186 (62.9%), hypofibrinogenemia in 118 of 196 (60.2%), splenomegaly in 125 of 188 (66.5%), and impaired NK cell activity in 16 of 25 (64.0%). In addition, hepatomegaly was noted in 57 of 195 patients (29.2%). After a median follow-up of 58.3 months, median OS was 62 days (95% CI 40-110) from day of diagnosis. In a multivariable Cox proportional hazards model with moderate discrimination (c-index=0.75), after adjusting for age at diagnosis and sex, T-cell lymphoma–driven HLH (HR 1.78, 95% CI 1.05–3.00, p = 0.03) and elevated blood urea nitrogen (median 51.0 mg/dL, IQR 27.9–99.1; HR 2.07, 95% CI 1.37–3.13, p < 0.005) were independently associated with shorter OS Conclusions: In this cohort of adult patients with HLH, malignancy was found to be the most common trigger for HLH. T-cell malignancies in particular were strongly correlated with poor survival. Elevated blood urea nitrogen at diagnosis also identified patients at significantly higher risk of death, consistent with other critical illnesses that can present with multi-organ failure. These findings emphasize the need for adult-specific prognostic tools incorporating disease etiology and organ dysfunction markers to better stratify risk and guide clinical management in adult-onset HLH.

Abstract Background Antiphospholipid syndrome (APS) is diagnosed when vascular thrombosis or pregnancy morbidity occurs in the presence of persistent antiphospholipid antibodies (aPL). Although IgM-isotype antibodies are part of the laboratory criteria, their clinical value remains uncertain. We evaluated real-world aPL testing patterns to quantify the prevalence of isolated IgM positivity. Methods We analyzed aPL testing data across the Mayo Clinic sites between January 2006 and July 2025, lined up with the publication of the revised Sapporo (Sydney) classification criteria. For each patient, we identified the first time in which any aPL test was performed. We assessed available results for Lupus anticoagulant (LA), anticardiolipin (aCL) isotypes IgG and IgM, and anti–beta 2 glycoprotein (B2GP1) isotypes IgG and IgM. Positivity rates were calculated for each marker, and a subgroup of patients who had results for all three test categories at the initial workup was identified. In this cohort, we assessed the distribution of single, double, and triple positivity. We also quantified the number and percentage of patients who were positive only for IgM isotypes (aCL or B2GP1), with negative LA and IgG at initial testing. Antibodies were considered positive based on international criteria and internal standards. aCL and B2GP1 were positive if ≥40 units. LA positivity followed ISTH SSC guidelines, requiring demonstration of a phospholipid-dependent inhibitor in the following assays: screening, mixing, and confirmatory steps in DRVVT or aPTT-based platelet neutralization procedure (PNP), Staclot LA delta and HEX LA delta assays. Criteria for a positive result was as follows: DRVVT: prolonged screen and inhibited mix with screen/confirm ratio >1.2; Staclot LA delta: >7 seconds; PNP: shortening of the APTT clotting time with PNP by ≥5 seconds before 2023 and ≥2 seconds thereafter; HEX LA delta >13 seconds. Results A total of 99,814 unique patients underwent testing for at least one aPL marker. The most frequently tested was LA (n = 75,085), with a positivity rate of 10.29% (7,730/75,085). Among antibody isotypes, positivity rates were 1.2% (846/69,539) for aCL IgG, 1.7% (1,198/69,640) for aCL IgM, 1.9% (732/37,791) for B2GP1 IgG, and 2.0% (762/37,601) for B2GP1 IgM. Among the 30,274 patients who underwent simultaneous testing for LA, aCL IgG/IgM, and B2GP1 IgG/IgM, 1.3% (n = 407) were triple-positive, 1.4% (n = 427) were double-positive, and 9.9% (n = 3,009) had a single positive marker. The remaining 87.3% (n = 26,431) tested negative for all three. Of the 3,009 patients with only one positive marker, 9.8% (n = 296) were positive exclusively for aCL IgM, and 7.4% (n = 224) were positive exclusively for B2GP1 IgM. Among all fully tested patients, 2.2% (668/30,274) were positive for only IgM isotypes (either aCL or B2GP1) in the absence of IgG and LA positivity. Specifically, 0.9% (n = 296) were exclusively positive for aCL IgM and 0.7% (n = 224) for B2GP1 IgM. Additionally, 0.5% (n = 148) were simultaneously positive for both aCL IgM and B2GP1 IgM, without associated IgG or LA markers. Had only IgG and LA been assayed, 17.4 % (668/3843) of initially positive patients—and one-third of those classified as triple-positive—would have been missed. Conclusion Within this large-scale analysis of real-world APS test ordering practice, less than one-third of orders included a comprehensive characterization. Isolated IgM positivity, defined as aCL or B2GP1 IgM in the absence of IgG and LA, was infrequent yet represents a sizable proportion of initial positive aPL testing. How these results impact APS diagnosis and management of APS requires further study.

Abstract Background: In 2022, Medicare alone spent $42.1 billion on prescription drugs, with antineoplastic and classical hematology drugs accounting for 44% and 8% of the total, respectively (2024 MedPAC Data Book). While antineoplastic drugs have been extensively studied, classical hematology drugs have received comparatively little attention. We analyzed US Food and Drug Administration (FDA) approvals of classical hematology drugs over the past 30 years and examined their per-patient costs and annual total US sales. Methods: We identified all classical hematology drugs (those prescribed by hematologist/oncologists for non-malignant indications) approved by the FDA from January 1, 1995 to December 31, 2024, including novel pharmaceuticals (synthesized from chemical compounds), biologics (derived from living organisms), and biosimilars (highly similar, but not identical, to biologics previously approved). Cost estimates for 2024 were based on wholesale acquisition costs (WAC), using annual WAC for continuous-duration treatments and typical course WAC for fixed-duration treatments. WAC and US gross sales data for 2024 were obtained from IPD Analytics (Aventura, FL). Results: A total of 98 classical hematology drugs were approved over the past 30 years—11% in 1995–2004, 26% in 2005–2014, and 63% in 2015–2024. These included pharmaceuticals (36%), biologics (54%), and biosimilars (10%). Six gene therapies received approval: 3 for hemophilia and 1 each for sickle disease, beta thalassemia, and sickle cell disease/beta thalassemia (dual indication). Common categories of indications included bleeding (31%), anemia (30%), neutropenia (9%), and thrombocytopenia (9%). Leading diagnoses were hemophilia (25%), chemotherapy-induced neutropenia (9%), thromboembolism (8%), paroxysmal nocturnal hemoglobinuria (PNH; 7%), anemia of chronic kidney disease (6%), iron deficiency anemia (6%), and immune thrombocytopenia (5%). The median cost for gene therapies was $2.9 million per treatment (range: $2.2 million–$3.5 million). Among non-gene therapies, median costs were $3,000 per course for fixed-duration treatments (range: $64–$378,000) and $467,000 annually for continuous-duration treatments (range: $2,400–$1.8 million). The most expensive fixed-duration treatments targeted hemophagocytic lymphohistiocytosis ($378,000/8-week course), while the most expensive continuous-duration treatments were for hemophilia (median: $630,000/year; range: $270,000–$853,000). Estimated 2024 US gross sales across all drugs exceeded $70 billion. Top-selling indications included thromboembolism ($43.5 billion), hemophilia ($6.9 billion), immune thrombocytopenia ($4.9 billion), PNH ($4.7 billion), chemotherapy-induced neutropenia ($2.8 billion), anemia of chronic kidney disease ($2.0 billion), and iron deficiency anemia ($1.8 billion). Total sales for all gene therapies combined were $143 million. Six drugs have been discontinued (year approved/year discontinued/reason): betrixaban (2017/2020/business), daprodustat (2023/2024/business), fidanacogene elaparvovec (2024/2025/business), oprelvekin (1997/2011/business), peginesatide (2012/2013/safety), and voxelotor (2019/2024/safety). There are limitations to our study. Some drugs have non-classical hematology indications (anticoagulants in atrial fibrillation; luspatercept in myelodysplastic neoplasm) and/or may also be prescribed by non-classical hematologists (erythropoiesis stimulating agents by nephrologists and medical oncologists). We were unable to disaggregate the sales data in these situations. Therefore, the annual sales for certain indications may be overestimated. Conclusions: Classical hematology drugs contribute substantially to US prescription drug spending, with over $70 billion in annual sales and medications for thromboembolism accounting for over half of the costs. Approvals have accelerated over the past three decades, doubling each decade. Biologics and biosimilars now represent two-thirds of approvals. Continuous-duration treatments, particularly for rare hereditary diseases like hemophilia, carry significant financial burden, with annual costs per patient often exceeding $0.5 million. In these conditions, if gene therapies demonstrate durable efficacy, they may prove to be cost-effective alternatives. As more gene therapies are developed, evaluating their long-term value relative to chronic high-cost treatments will be essential for shaping future reimbursement and access strategies.

Abstract Introduction: Only 30% of patients (pts) presenting with abnormal bleeding symptoms receive a clear diagnosis, with many classified as having bleeding disorder of unknown cause, or BDUC (Baker et al. 2021). Currently, the recommended diagnostic workup for BDUC by the International Society on Thrombosis and Haemostasis (ISTH) includes plasmatic assays for coagulation factors, von Willebrand factor (vWF) antigen/activity, and platelet function testing (PFT), specifically platelet function analyzer-100 (PFA-100) and light transmission aggregometry (LTA). However, PFTs are not widely available and cannot be mailed to reference laboratories. We studied the diagnostic yield of an expanded testing panel which includes quantitative platelet glycoprotein flow cytometry (GpFL) and platelet electron microscopy (PTEM), which we have optimized for specimen mailing. Methods: We conducted a minimal risk, retrospective study by reviewing the electronic health records of pts (18 years and older) who were seen in the Coagulation Clinic of a tertiary academic medical center for evaluation of a bleeding disorder between October 2017 and June 2025. Testing included plasma-based assays including PT, APTT, vWF assay, FVIII, FIX, FXIII screen, and thrombin time (and additional reflex assays as needed). At the discretion of the treating clinician, PFTs (PFA-100 and LTA), GpFL, PTEM, and fibrinolysis assays (plasminogen activator inhibitor-1 antigen [PAI-1 Ag] and alpha-2 plasmin inhibitor) were included. We abstracted clinical data on pt demographics, ISTH bleeding scores, and the results of coagulation testing. Pts with an established diagnosis of a bleeding disorder, underlying malignancy, and those who did not have plasma-based coagulation testing were excluded from this study. Results: 109 pts met study criteria, and 82.6% were females (n = 90) with a median age of 45 years (range = 18-88 years). The median ISTH-BAT score was 7 (range: 2-21). About half of the pts, 49.5% (n = 54), had normal coagulation profiles and PFTs. All 54 had PTEM performed, of which 14.8% (n = 8) were abnormal (alpha and/or dense granule deficiencies). 85.2% (n = 46) had GpFL testing performed, with one showing reduced Gp2b/CD42 and Gp3a/CD61 expression, four showing reduced Gp1a/CD49b expression, and three showing reduced GpVI expression. Half of the pts, 50.5% (n = 55) had an abnormal coagulation profile from plasma and/or PFTs, of which 20% (n = 11) had a clinically significant coagulation factor deficiency (FV, FVII, FX). Roughly 9.1% (n = 5) had type 1 vWD of which 1 also had PAI-1 deficiency. One pt had isolated PAI-1 deficiency. Abnormal coagulation profiles were noted in 53 pts who had PFA-100 and LTA done, and both tests were normal in 22.6% (n = 12). Within the abnormal coagulation profile group, 10.9% (n = 6) had ultrastructural abnormalities on PTEM (dense and alpha granule abnormalities). Majority of the pts (n = 46) had GpFL done, and one had abnormal reductions in Gp1b-aCD42b, three in Gp1aCD49b, and seven in GPVI. Comparison of the ISTH BAT score between the normal and abnormal coagulation profiles/PFTs groups by non-parametric (Mann-Whitney U test) and parametric (Welch's t-test) showed no significant difference (p = 0.56 and p = 0.87) respectively. Conclusion: In this cohort of pts with abnormal bleeding, standard recommended testing resulted in a diagnosis in 66.4% pts. The remainder would have been classified as BDUC. The addition of GpFL and PTEM resulted in establishing a diagnosis that explains the bleeding phenotype in 14.8% of pts with an otherwise normal coagulation profile and PFT. Although abnormal PFTs indicate a platelet function defect, GpFL and PTEM may further define the abnormalities particularly differentiating syndromic from non-syndromic inherited platelet disorders. Additional studies are needed to confirm our findings and explore the possibility of addition of GpFL and PTEM for patients with BDUC.

ABSTRACT BACKGROUND Platelet factor 4-polyanion enzyme-linked immunosorbent assays (ELISAs) are considered highly sensitive for diagnosing heparin-induced thrombocytopenia (HIT), such that current practice guidelines recommend use of ELISA-negative results to exclude HIT. Once HIT is ruled out, alternative, non-heparin-based anticoagulant treatments are ceased, and heparin reintroduction frequently occurs. METHODS Antigen-based and PF4-dependent functional testing were used to study PF4/polyvinyl sulfonate ELISA-negative platelet-activating antibodies in HIT-suspected patients and mice immunized with PF4/heparin. RESULTS Three patients with clinical presentations consistent with HIT tested negative in an ELISA using PF4-polyvinylsulfonate (PF4/PVS), an antigenic target very commonly used for HIT antibody detection. All three patients demonstrated PF4-dependent platelet activation in functional testing that was sensitive to blockade of platelet FcγRIIa receptors and inhibited by high concentrations of heparin, consistent with pathogenic HIT antibodies. Functional testing-based screening of 500 ELISA-negative patients identified three patients whose sera activated platelets in a PF4- and FcγRIIa-dependent manner, and had clinical histories consistent with HIT. Five of the six ELISA-negative HIT patients were re-exposed to heparin, which precipitated a decrease in platelet counts in all re-exposed patients, and one patient developed a new thrombus. To advance the study of ELISA-negative HIT antibodies, mice were immunized with PF4/heparin, and functional and antigenic assays were simultaneously used to successfully identify an ELISA-negative, PF4-dependent platelet-activating murine monoclonal antibody that recapitulated the serological characteristics of ELISA-negative HIT patients. CONCLUSIONS Recognition of ELISA-negative HIT is critical to avoid harm due to the cessation of alternative anticoagulation therapy and re-exposure of these patients to heparin.

469 Background: Febrile neutropenia (FN) is a potentially life-threatening complication of myelosuppressive chemotherapy. Multiple professional organizations, including the American Society of Clinical Oncology (ASCO), Infectious Diseases Society of America (IDSA), National Institute for Health and Care Excellence (NICE), European Society for Medical Oncology (ESMO), and National Comprehensive Cancer Network (NCCN), have developed clinical guidelines addressing FN management. The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) framework offers a structured method for assessing the evidence underlying these recommendations. Methods: A comparative analysis was conducted across guidelines. Key domains, including definitions, risk stratification, empiric antimicrobial therapy, duration of antimicrobial therapy, use of granulocyte colony-stimulating factor (G-CSF), and antimicrobial prophylaxis were assessed. Recommendations were analyzed for concordance and the certainty of supporting evidence was appraised using the GRADE framework. The certainty of the evidence was graded as high, moderate, low, or very low. Results: All five guidelines uniformly defined FN as fever ≥38.3°C or sustained ≥38.0°C accompanied by neutropenia (absolute neutrophil count <500 cells/µL), despite very low-certainty evidence supporting these specific thresholds. Risk stratification using validated tools, such as the Multinational Association for Supportive Care in Cancer (MASCC) score and the Clinical Index of Stable Febrile Neutropenia (CISNE), is recommended based on moderate-certainty evidence. Empiric monotherapy with anti-pseudomonal beta-lactam agents is recommended across guidelines and supported by high-certainty evidence. Antifungal therapy is recommended for persistent fever beyond 4–7 days in high-risk patients based on low-certainty data. Variability was noted in the suggested duration of antibacterial therapy and the role of therapeutic G-CSF based on low-certainty evidence. Recommendations for antimicrobial prophylaxis are consistent across high-risk populations. Conclusions: Despite broad agreement in foundational management principles for febrile neutropenia, differences exist in the application of therapeutic G-CSF and the duration of empiric antibiotics. These findings underscore the need for high-quality clinical trials to inform harmonized, evidence-based recommendations. This synthesis identifies priority areas for stewardship initiatives and quality-of-care improvement.

Abstract Immune thrombocytopenia (ITP) carries an increased risk of thrombosis, which may be further amplified by splenectomy and thrombopoietin receptor agonists (TPO-RAs). Although each intervention has been individually studied for its thrombotic risk, data are lacking on the safety of postsplenectomy TPO-RA use. We conducted a retrospective cohort study of adult patients with ITP who underwent splenectomy between 2011 and 2024. Patients were stratified on the basis of postsplenectomy TPO-RA use. The primary outcome was incidence of thrombosis. Secondary outcomes included bleeding, mortality, and hematologic response. Time-to-event analyses and multivariate Cox regression were performed. Among 88 patients, 37 (42%) patients received TPO-RAs after splenectomy. Thrombosis occurred in 17 patients in the TPO-RA group vs 14 patients in the non–TPO-RA group (P = .07). The 10-year cumulative incidence of thrombosis was numerically higher in the TPO-RA group (57% vs 36%), with clustering of events within the 3 months of postsplenectomy TPO-RA initiation. Venous events predominated; arterial events were rare. No significant differences were observed in bleeding or mortality rates between groups. Platelet counts alone did not independently affect bleeding or thrombosis. TPO-RA use after splenectomy was not significantly associated with increased thrombosis risk. However, early initiation may coincide with a high-risk period, and the sustained numerical difference in cumulative incidence throughout follow-up highlights potential clinical relevance. These findings support the need for individualized thromboprophylaxis and prospective evaluation of TPO-RA safety in this setting.