Fibrinolysis and bleeding of unknown cause

Accelerated Fibrinolysis: A Tendency to Bleed?

Hyperfibrinolysis is rarely investigated as an underlying mechanism in patients with mild-to-moderate bleeding disorders (MBDs) and bleeding disorders of unknown cause (BDUC). Hereditary hyperfibrinolytic disorders, including α2-antiplasmin (α2-AP) deficiency, plasminogen activator inhibitor type 1 (PAI-1) deficiency, Quebec platelet disorder, and tissue plasminogen activator (tPA) excess, present with mild-to-moderate bleeding symptoms that are common in patients with MBD or BDUC, but may also manifest as life-threatening bleeding. This review summarizes the available data on hyperfibrinolysis in MBD and BDUC patients, and its assessment by various methods such as measurement of fibrinolytic factors, global hemostatic assays (e.g., viscoelastic testing, turbidity-based plasma clot lysis), and fluorogenic plasmin generation (PG). However, evidence on the relationship between hyperfibrinolytic profiles and bleeding severity is inconsistent, and, although found in some coagulation factor deficiencies, has not been universally observed. In BDUC, increased tPA activity and paradoxical increases in thrombin-activatable fibrinolysis inhibitor and α2-AP have been reported. Some studies reported no change in PAI-1 levels, while others observed reduced PAI-1 levels in a significant subset of patients. The tPA-ROTEM (tPA-rotational thromboelastometry) assay identified a hyperfibrinolytic profile in up to 20% of BDUC patients. PG analysis revealed a paradoxically reduced peak plasmin, but showed strong predictive power in differentiating BDUC patients from healthy controls. Although global fibrinolytic assays may help identify hyperfibrinolytic profiles as a potential cause of increased bleeding in some MBD or BDUC patients, the utility of measuring fibrinolytic factors requires further investigation. Tranexamic acid is commonly used to treat hereditary hyperfibrinolysis and is also recommended in MBD/BDUC patients prior to hemostatic challenges.

Plasmin generation analysis in patients with bleeding disorder of unknown cause

ABSTRACT

Bleeding disorder of unknown cause (BDUC) is a diagnosis of exclusion after evaluation of plasma coagulation and platelet function. Patients with BDUC (n = 375) recorded in the Vienna Bleeding Biobank were analyzed in comparison with healthy controls (HCs; n = 100) in this case-control study. Plasmin generation (PG) parameters were analyzed using calibrated fluorescence detection in citrated plasma. Turbidimetric plasma clot formation/lysis of 293 (78%) patients with BDUC and confocal microscopy of clots from representative patients with BDUC (n = 6) and HCs (n = 9) were assessed. In the PG analysis, patients with BDUC exhibited lower velocity and peak plasmin levels but a higher endogenous plasmin potential than HCs. Peak plasmin levels correlated with maximum clot absorbance but not with clot lysis time. Clot absorbance is an indicator of clot fiber density. Confocal microscopy analysis revealed a tendency towards thicker fibers in clots of patients with BDUC, which negatively correlated with peak plasmin (r = -0.561; P = .030). Peak plasmin correlated weakly with factor XIII, but not with other fibrinolytic factors (alpha2-antiplasmin, thrombin activatable fibrinolysis inhibitor, or plasminogen activator inhibitor 1) or bleeding severity. A model comprising fibrinogen and parameters of PG yielded high predictive power in discriminating between patients with BDUC and HCs across a fivefold stratified cross validation (80% of data; mean area under the curve [AUC], 0.847). The model generalized well to unseen data (20% of data; AUC, 0.856). Overall, patients with BDUC counterintuitively exhibited reduced peak plasmin levels, potentially related to altered clot structure.

Fibrinolysis is impaired in patients with primary immune thrombocytopenia

BACKGROUND

Patients with primary immune thrombocytopenia (ITP) have an increased risk of thrombosis, which may be due to altered fibrinolysis.

OBJECTIVES

To elucidate the clinical impact of delayed fibrinolysis in ITP patients.

METHODS

A turbidimetric clot formation and lysis assay and a fluorometric plasmin generation (PG) assay were performed, and levels of plasminogen activator inhibitor-1 (PAI-1), tissue plasminogen activator (tPA), tPA-PAI-1 complexes, α2-antiplasmin, thrombin activatable fibrinolysis inhibitor, and D-dimer were assessed in 86 adult primary ITP patients and 78 healthy controls (HCs).

RESULTS

ITP patients showed significantly delayed clot formation, increased clot density, and prolonged clot lysis time (CLT) compared with HCs, with a median (IQR) CLT of 28.0 (13.7-34.7) minutes in patients and 17.3 (12.0-28.0) minutes in HCs, while in the PG assay, only the lag time was prolonged. In ITP patients compared with controls, PAI-1 was higher (1.2 [0.8-2.6] vs 1.1 [0.6-2.1] U/mL) and tPA antigen and activity were lower (tPA antigen: 2.6 [1.1-4.4] vs 3.7 [3.2-4.7] ng/mL; tPA activity ≤ 0 U/mL: 26% vs 7%). TPA-PAI-1 complex levels were positively associated with CLT in multiple linear regression analysis (β = 0.241; P = .019), whereas PG parameters were not associated with CLT. Six patients who developed thrombosis during follow-up had higher levels of tPA-PAI-1 complexes.

CONCLUSION

Prolonged CLT and delayed onset of PG may indicate a hypofibrinolytic tendency in ITP patients, as also indicated by high PAI-1 and low tPA levels. No association was found between fibrinolytic potential and the bleeding phenotype, whereas higher tPA-PAI-1 complex levels were associated with prolonged CLT and increased in patients with future thrombosis.

Examining variability in the diagnosis and management of people with bleeding disorders of unknown cause: communication from the ISTH SSC Subcommittee on von Willebrand Factor

BACKGROUND

Bleeding disorder of unknown cause (BDUC) is characterized by a bleeding phenotype in the setting of normal hemostatic testing. No standardized diagnostic criteria or treatment algorithms exist for people with BDUC. To address the unmet need, the International Society on Thrombosis and Haemostasis von Willebrand Factor Scientific Subcommittee performed a real-world survey aimed at addressing knowledge gaps, developing consensus pathways, and ultimately improving care.

OBJECTIVES

We sought to determine current international clinical practices in the investigation, registration, and treatment of people with BDUC internationally.

METHODS

An online structured survey was conducted of healthcare providers who managed patients with bleeding disorders using the ISTH RedCap tool.

RESULTS

Two hundred sixteen respondents from 39 countries were included in the final analysis. The clinical assessment of those with a possible bleeding disorder varied, with only 55% excluding hypermobility but high levels (80%) of bleeding assessment tool usage. In hemostatic testing, only the prothrombin time and activated partial thromboplastin time tests gained universal support. Tranexamic acid was favored for prophylaxis for minor (71%)/major (59%) surgeries and pregnancy (58%), but advice on the treatment if bleeding occurred was heterogeneous. The management of heavy menstrual bleeding in women despite combined oral contraceptive pill use also proved challenging, with healthcare providers selecting multiple alternative strategies.

CONCLUSION

Significant variation exists in the recognition, registration, and management of people with BDUC worldwide. This survey emphasizes the need for consensus pathways to diagnose and treat BDUC to standardize and improve care for patients internationally.

Bleeding Disorder of Unknown Cause: A Diagnosis of Exclusion

Patients with an unexplained mild to moderate bleeding tendency are diagnosed with bleeding disorder of unknown cause (BDUC), a classification reached after ruling out other mild to moderate bleeding disorders (MBD) including von Willebrand disease (VWD), platelet function defects (PFDs), coagulation factor deficiencies (CFDs), and non-hemostatic causes for bleeding. This review outlines our diagnostic approach to BDUC, a diagnosis of exclusion, drawing on current guidelines and insights from the Vienna Bleeding Biobank (VIBB). According to guidelines, we diagnose VWD based on VWF antigen and/or activity levels ≤50 IU/dL, with repeated VWF testing if VWF levels are <80 IU/dL. This has been introduced in our clinical routine after our findings of diagnostically relevant fluctuations of VWF levels in a high proportion of MBD patients. PFDs are identified through repeated abnormalities in light transmission aggregometry (LTA), flow cytometric mepacrine fluorescence, and glycoprotein expression analysis. Nevertheless, we experience diagnostic challenges with regard to reproducibility and unspecific alterations of LTA. For factor (F) VIII and FIX deficiency, a cutoff of 50% is utilized to ensure detection of mild hemophilia A or B. We apply established cutoffs for other rare CFD being aware that these do not clearly reflect the causal role of the bleeding tendency. Investigations into very rare bleeding disorders due to hyperfibrinolysis or increase in natural anticoagulants are limited to cases with a notable family history or distinct bleeding phenotypes considering cost-effectiveness. While the pathogenesis of BDUC remains unknown, further explorations of this intriguing area may reveal new mechanisms and therapeutic targets.

Standardization of definition and management for bleeding disorder of unknown cause: communication from the SSC of the ISTH

In many patients referred with significant bleeding phenotype, laboratory testing fails to define any hemostatic abnormalities. Clinical practice with respect to diagnosis and management of this patient cohort poses significant clinical challenges. We recommend that bleeding history in these patients should be objectively assessed using the International Society on Thrombosis and Haemostasis (ISTH) bleeding assessment tool. Patients with increased bleeding assessment tool scores should progress to hemostasis laboratory testing. To diagnose bleeding disorder of unknown cause (BDUC), normal complete blood count, prothrombin time, activated partial thromboplastin time, thrombin time, von Willebrand factor antigen, von Willebrand factor function, coagulation factors VIII, IX, and XI, and platelet light transmission aggregometry should be the minimum laboratory assessment. In some laboratories, additional specialized hemostasis testing may be performed to identify other rare causes of bleeding. We recommend that patients with a significant bleeding phenotype but normal laboratory investigations should be registered with a diagnosis of BDUC in preference to other terminology. Global hemostatic tests and markers of fibrinolysis demonstrate variable abnormalities, and their clinical significance remains uncertain. Targeted genomic sequencing examining candidate hemostatic genes has a low diagnostic yield. Underlying BDUC should be considered in patients with heavy menstrual bleeding since delays in diagnosis often extend to many years and negatively impact quality of life. Treatment options for BDUC patients include tranexamic acid, desmopressin, and platelet transfusions.

Targeted exome analysis in patients with rare bleeding disorders: data from the Rare Bleeding Disorders in the Netherlands study

Background

Rare coagulation factor deficiencies and disorders of fibrinolysis (defined as rare bleeding disorders [RBDs]) present with a heterogeneous bleeding phenotype, and bleeding severity is difficult to predict.

Objectives

Describe underlying rare genetic variants in the Dutch RBD population and investigate the relationship between genotype, laboratory phenotype, and clinical phenotype.

Methods

The Rare Bleeding Disorders in the Netherlands is a cross-sectional, nationwide study conducted between October 1, 2017, and November 30, 2019. Bleeding scores and blood samples were collected during a single study visit. Coagulation factor levels were measured centrally, and targeted exome analysis was performed on 156 genes involved in thrombosis and hemostasis. Pathogenicity was assigned according to the Association for Clinical Genetic Science guidelines.

Results

Rare genetic variants specific to the diagnosed RBD were found in 132 of 156 patients (85%). Of the 214 rare genetic variants identified, 57% (n = 123) were clearly pathogenic, 19% (n = 40) were likely pathogenic, and 24% (n = 51) were variants of unknown significance. No explanatory genetic variants were found in patients with plasminogen activator inhibitor type 1 deficiency or hyperfibrinolysis. A correlation existed between factor activity levels and the presence of a genetic variant in the corresponding gene in patients with rare coagulation factor deficiencies and alpha-2-antiplasmin deficiency. Co-occurrence of multiple genetic variants was present in a quarter of patients, but effect on phenotype remains unclear.

Conclusion

Targeted exome analysis may offer advantages over single-gene analysis, emphasized by a number of combined deficiencies in this study. Further studies are required to determine the role of co-occurring hemostasis gene variants on the bleeding phenotype in RBDs.

Abnormal bleeding after lumbar vertebrae surgery because of acquired factor XIII deficiency: A case report and literature review

RATIONALE

Abnormal bleeding due to low fibrinogen (Fib) and coagulation factor XIII (FXIII) levels after lumbar vertebral surgery is exceedingly rare. Excessive bleeding is also associated with secondary hyperfibrinolysis. This report presents a case of abnormal incision bleeding caused by coagulation factor XIII deficiency (FXIIID) and secondary hyperfibrinolysis in a state of low fibrinogen after lumbar vertebral surgery.

PATIENT CONCERNS

A middle-aged woman experienced prolonged incision and excessive bleeding after lumbar vertebral surgery.

DIAGNOSIS

Combined with coagulation factors, coagulation function tests, and thromboelastography, the patient clinical presentation supported the diagnosis of FXIIID and secondary hyperfibrinolysis in a hypofibrinogenemic state.

INTERVENTIONS

Cryoprecipitat, Fresh Frozen Plasma, Fibrinogen Concentrate, Leukocyte-depleted Red Blood Cells, Hemostatic (Carbazochrome Sodium Sulfonate; Hemocoagulase Bothrops Atrox for Injection; Tranexamic Acid).

OUTCOMES

After approximately a month of replacement therapy and symptom treatment, the patient coagulation function significantly improved, and the incision healed without any hemorrhage during follow-up.

LESSONS

Abnormal postoperative bleeding may indicate coagulation and fibrinolysis disorders that require a full set of coagulation tests, particularly coagulation factors. Given the current lack of a comprehensive approach to detect coagulation and fibrinolysis functions, a more comprehensive understanding of hematology is imperative. The current treatment for FXIIID involves replacement therapy, which requires supplementation with both Fib and FXIII to achieve effective hemostasis.

Investigating patients for bleeding disorders when most of the "usual" ones have been ruled out

A State of the Art lecture titled "Investigating Patients for Bleeding Disorders When Most of the Usual Ones Have Been Ruled Out" was presented at the International Society on Thrombosis and Haemostasis Congress in 2023. Mild to moderate bleeding disorders (MBDs) in patients in whom no diagnosis of an established disorder, such as platelet function defect, von Willebrand disease, or a coagulation factor deficiency, can be identified are classified as bleeding disorders of unknown cause (BDUCs). Prospective data from the Vienna Bleeding Biobank and other studies have revealed a high proportion of BDUCs of up to 70% among patients with MBD who have a similar bleeding phenotype as other MBDs. As BDUC is a diagnosis of exclusion, the accuracy of the diagnostic workup is essential. For example, repeated testing for von Willebrand disease should be considered if von Willebrand factor values are <80 IU/dL. Current evidence does not support the clinical use of global assays such as thromboelastography, platelet function analyzer, or thrombin generation potential. Rare and novel bleeding disorders due to genetic variants in fibrinolytic factors or natural anticoagulants are rare and should only be analyzed in patients with specific phenotypes and a clear family history. In BDUC, blood group O was identified as a risk factor for increased bleeding severity and bleeding risk after hemostatic challenges. Future studies should improve the phenotypical characterization and ideally identify novel risk factors in BDUC, as a multifactorial pathogenesis is suspected. Finally, we summarize relevant new data on this topic presented during the 2023 International Society on Thrombosis and Haemostasis Congress.