Factor V inhibitors

Interpreting coagulation mixing study results in the era of direct oral anticoagulants

Interpretation of coagulation mixing studies is complicated by interference arising from direct oral anticoagulants (DOACs), which are increasingly prescribed. In this retrospective study, we reviewed 1035 consecutive coagulation mixing studies performed from 2017 to 2021. Three hundred and ninety-nine cases with normal prothrombin time (PT) and activated partial thromboplastin time (aPTT) were excluded. aPTT mixing studies were performed at time 0 and after 60 min of incubation. We confirmed the presence of interfering factors with additional laboratory testing, medication records, and medical history. Mixing corrected most prolonged PT samples (93%), but 32 cases showed incomplete correction. Of these 32 cases, 18 were confounded by DOAC use, and 3 by factor V (FV) inhibitor. We observed an unusual pattern of prolongation of aPTT after incubation, which was previously considered a characteristic of specific factor inhibitors, most commonly FVIII inhibitor. However, we found that lupus anticoagulant (28%) and DOAC (25%) contributed to this pattern similarly as specific factor inhibitors (28%). Coagulation laboratories should be aware of interference arising from DOACs and other factors in PT/aPTT mixing studies, especially in some unusual correction patterns.

Activated Partial Thromboplastin Time and Prothrombin Time Mixing Studies: Current State of the Art

Mixing studies have long been in the clinical laboratory armamentarium for investigating unexpected, prolonged activated partial thromboplastin time (aPTT) or prothrombin time (PT). The purpose of the mixing study is to identify whether the aPTT/PT prolongation is secondary to a factor deficiency versus an inhibitor, which would present as a "corrected" and "noncorrected" mixing study, respectively. The differentiation between a factor deficiency and inhibitor may likely further direct clinical decisions, including additional diagnostic testing or factor replacement therapy. While aPTT/PT mixing studies are simple tests to perform, there is a lack of standardization for both the testing protocol and the interpretation of what is considered to be a corrected or noncorrected mixing study result. This review will describe the common indications for the mixing test, preanalytic variables that may affect mixing study performance, and describe several methods for interpreting the results of aPTT and PT mixing tests.

International Council for Standardization in Haematology recommendations for laboratory measurement of factor VIII and FIX type I inhibitors

This guidance document has been prepared on behalf of the International Council for Standardisation in Hematology. The aim of the document is to provide guidance and recommendations on the measurement of factor VIII (FVIII) and factor IX (FIX) inhibitors. After an introduction on the clinical background and relevance of factor VIII and factor IX inhibitor testing, the following aspects of laboratory testing are included: screening for inhibitors, assay principle, sample requirements, testing requirements and interpretation, quality assurance, interferences and recent developments. This guidance document focusses on recommendations for a standardised procedure for the laboratory measurement of FVIII and FIX type I inhibitors. The recommendations are based on published data in peer-reviewed literature and expert opinion.

Idiopathic factor V inhibitor in a patient starting haemodialysis

A 74-year-old Pacific Island man with end-stage renal failure planning to start haemodialysis presented with persistent bleeding after tunnelled dialysis catheter insertion. The laboratory findings revealed a prolonged activated partial thromboplastin time of 118 s, prothrombin ratio of 4.2, factor V activity of <2% and a factor V inhibitor of 40 Bethesda Units. No clear underlying aetiology was identified. The bleeding settled with conservative measures and the factor V inhibitor was successfully treated with oral cyclophosphamide for 6 weeks.

Autoimmune Diseases Affecting Hemostasis: A Narrative Review

Hemostasis reflects a homeostatic mechanism that aims to balance out pro-coagulant and anti-coagulant forces to maintain blood flow within the circulation. Simplistically, a relative excess of procoagulant forces can lead to thrombosis, and a relative excess of anticoagulant forces can lead to bleeding. There are a wide variety of congenital disorders associated with bleeding or thrombosis. In addition, there exist a vast array of autoimmune diseases that can also lead to either bleeding or thrombosis. For example, autoantibodies generated against clotting factors can lead to bleeding, of which acquired hemophilia A is the most common. As another example, autoimmune-mediated antibodies against phospholipids can generate a prothrombotic milieu in a condition known as antiphospholipid (antibody) syndrome (APS). Moreover, there exist various autoimmunity promoting environments that can lead to a variety of antibodies that affect hemostasis. Coronavirus disease 2019 (COVID-19) represents perhaps the contemporary example of such a state, with potential development of a kaleidoscope of such antibodies that primarily drive thrombosis, but may also lead to bleeding on rarer occasions. We provide here a narrative review to discuss the interaction between various autoimmune diseases and hemostasis.

Testing for Lupus Anticoagulants

Lupus anticoagulant (LA) is one of the three criteria antiphospholipid antibodies (aPLs) employed in classification, and by default diagnosis, of antiphospholipid syndrome (APS). Detection of LA is not via calibrated assays but is based on functional behavior of the antibodies in a medley of coagulation assays. A prolonged clotting time in a screening test is followed by demonstration of phospholipid dependence and inhibitory properties in confirmatory and mixing tests, respectively, which are modifications of the parent screening test. Complications arise because no single screening test is sensitive to every LA, and no test is specific for LA, because they are prone to interference by other causes of elevated clotting times. Several screening tests are available but the pairing of dilute Russell's viper venom time (dRVVT) with LA-sensitive activated partial thromboplastin time (aPTT) is widely used and recommended because it is proven to have good detection rates. Nonetheless, judicious use of other assays can improve diagnostic performance, such as dilute prothrombin time to find LA unreactive with dRVVT and aPTT, and the recently validated Taipan snake venom time with ecarin time confirmatory test that are unaffected by vitamin K antagonist and direct factor Xa inhibitor anticoagulation. Expert body guidelines and their updates have improved harmonization of laboratory practices, although some issues continue to attract debate, such as the place of mixing tests in the medley hierarchy, and areas of data manipulation such as assay cut-offs and ratio generation. This article reviews current practices and challenges in the laboratory detection of LA.

Acquired Factor V Inhibitor Complicated with Immune Thrombocytopenia

We herein report a patient with a high bleeding tendency as a result of acquired factor V inhibitor and immune thrombocytopenia (ITP). The administration of prednisolone increased the platelet count, but a fatal bleeding event occurred before platelet levels had sufficiently increased. Factor V is stored in not only plasma but also platelets, and platelet-derived factor V might play a local hemostatic role. Bleeding tendency may be high in rare cases where factor V inhibitor is complicated with severe thrombocytopenia. In such patients, physicians should consider aggressive hemostatic therapy, including plasma exchange, in addition to immunosuppressive therapy.

A Review of Coagulation Abnormalities of Autoimmune Acquired Factor V Deficiency with a Focus on Japan

Coagulation factor V (or FV for the purpose of medical safety) is an essential cofactor of coagulation factor X in the common pathway of coagulation; severe FV deficiency leads to a bleeding tendency. Although both congenital and acquired FV deficiencies are widely recognized, FV deficiency also presents as an autoimmune disorder. A nationwide survey on autoimmune coagulation factor deficiencies (AiCFDs) conducted in Japan by our Japanese Collaborative Research Group identified 24 new patients with autoimmune FV deficiency (AiFVD) in the past 5 years. Furthermore, our extensive literature search confirmed that 177 AiFVD cases have been reported in previous articles published from Japan. Patients with AiFVD in Japan were predominantly men, with age similar to those with other AiCFDs. AiFVD was confirmed as a relatively mild type of bleeding diathesis, associated with lower mortality rate than that for AiFVD and other AiCFDs reported in previous studies. Patients with AiFVD had variable FV inhibitor titers and both neutralizing anti-FV autoantibodies and nonneutralizing counterparts. Although spontaneous resolution occurs in some patients, timely initiation of hemostatic and immunosuppressive therapies helps arrest the bleeding and eliminate anti-FV antibodies, resulting in a high cumulative recovery rate. Immunological anti-FV antibody detection is recommended to avoid missing AiFVD cases for the presence of nonneutralizing anti-FV autoantibodies. Further investigation is necessary to clarify the long-term prognosis and optimal management of AiFVD.

Multiple thrombosis associated with Cytomegalovirus enterocolitis in an immunocompetent patient: a case report

BACKGROUND

Cytomegalovirus (CMV) is reported to have thrombogenic characteristics that activate factor X in vitro and stimulate the production of factor VIII and von Willebrand factor (vWF). Thrombosis associated with CMV infection is prevalent among immunocompromised patients and predominantly presents as a solitary large thrombus in the deep vein, pulmonary artery, splanchnic arteriovenous ducts, or other similar sites. Multiple thrombi, however, are rarely observed in such cases. Here, we report about an immunocompetent man with multiple microthrombi associated with CMV infection.

CASE PRESENTATION

A 72-year-old Japanese man who complained of abdominal pain was hospitalized with multiple colonic stenosis. He was later diagnosed with CMV enterocolitis and treated with ganciclover from Day 27 post-admission. During hospitalization, the patient developed thrombi in his fingers. He was initially treated with anticoagulant therapy (rivaroxaban); however, the therapy was discontinued owing to a prolonged activated thromboplastin time and an elevated international normalized ratio of prothrombin time. Instead, vitamin K and fresh-frozen plasma were administered. Nevertheless, his coagulation profile remained abnormal. Eventually, he developed colonic perforation and had to undergo emergency surgery. An intraoperative specimen showed several microthrombi in the middle and small arteriovenous ducts of his small and large intestines. The patient's coagulopathy improved preoperatively, and his overall condition improved postoperatively. Since the activation of ADAMTS13 was reduced remarkably, the thrombotic tendency was determined to be a thrombotic microangiopathy-like condition owing to increased vWF. We could not attribute the coagulopathy to any other cause except CMV infection; therefore, we concluded that this was a case of multiple thrombosis associated with CMV.

CONCLUSIONS

We present an extremely rare case of a patient with multiple thrombotic microangiopathy-like microthrombosis caused by CMV infection. Our findings suggest that CMV infection may be considered as a differential diagnosis for immunocompetent individuals who present with thrombosis of unspecified cause.

Acquired factor V inhibitor: Success of steroids in a patient with primary sclerosing cholangitis, ulcero haemorragic rectocolitis, biological Biermer's disease

We report the case of a 43-years-old Turkish man with acquired deficiency of factor V (FV) diagnosed in a usual screening before a (recto) colonoscopy. In the biologic explorations, activated partial prothrombin time (APTT) was abnormally high and prothrombin time (PT) was low 18IU/dL with no anticoagulant drugs (the PT was normal 6 months ago). The controlled level of factor V was 3IU/dL with FV antibodies (9 Bethesda Units/mL). This patient had a previous history of primary sclerosing cholangitis (2000) and ulcero haemorrhagic rectocolitis (2002) and a fortuitous biological Biermer's disease was revealed. Corticosteroids were prescribed at 1mg/kg/day with decreasing during 6 months, patient had gradual regression of the caused bleeding and FV became greater than 90%, F V antibodies decreased to less than 0.7 Bethesda Units/mL. This case illustrates the presence of FV inhibitor in an autoimmune gastrointestinal context with regression of clinical (caused) signs and antibodies with corticosteroids.

A rare case of acquired factor V inhibitor, during treatment with dabigatran for chronic atrial fibrillation, successfully treated with bypassing agents

Acquired factor V inhibitor represents a rare condition, described only in case reports. The use of activated bypassing agents in bleeding control could be of aid and improve the survival in symptomatic patients with acquired factor V inhibitor.

Autoimmune Factor V Deficiency That Took 16 Years to Diagnose due to Pseudodeficiency of Multiple Coagulation Factors

A 70-year-old man presented to our hospital with intramuscular hemorrhage in the right thigh. He had exhibited a tendency to bleed for the last 16 years and had visited several medical institutions, but no diagnosis had been made. Since the risk of sudden bleeding was assumed to be high due to his age, we decided to examine him in our department. A coagulation abnormality with prothrombin time-international normalized ratio (PT-INR) of 4.5 and activated partial thromboplastin time (aPTT) of 99.6 seconds was observed, but the platelet count, fibrinogen, and PIVKAII were within normal limits. Coagulation activities of factor V, VII, VIII, IX, X, XI, XII, and XIII were all reduced. Anti-factor VIII and IX antibodies which were measured by the Bethesda method, lupus anti-coagulant (diluted Russell snake venom time method) and anti-cardiolipin antibody were also positive. The results of these tests were comparable to those undertaken 15 years ago when they were scrutinized at the university hospital. We suspected the presence of anti-factor V antibodies because there was a dissociation between the thrombotest values measured and those calculated from the PT-INR. Moreover, cross-mixing test showed an immediate inhibitor pattern. Subsequently, factor V antibodies were confirmed by the immunoblot method and the diagnosis of autoimmune factor V deficiency was made. When factor V, which is downstream of the coagulation cascade, is inhibited, coagulation test using the one-stage clotting method shows a pseudolow value. Therefore, extensive abnormalities of coagulation factor activity and inhibitor assay should be interpreted with caution, and the presence of a high titer of factor V inhibitor should be considered.

Acquired factor V inhibitor: a nation-wide study of 38 patients

Acquired factor V inhibitor (AFVI) is an extremely rare disorder that may cause severe bleeding. To identify factors associated with bleeding risk in AFVI patients, a national, multicentre, retrospective study was made including all AFVI patients followed in 21 centres in France between 1988 and 2015. All patients had an isolated factor V (FV) deficiency <50% associated with inhibitor activity. Patients with constitutional FV deficiency and other causes of acquired coagulation FV deficiencies were excluded. The primary outcome was incident bleeding and factors associated with the primary outcome were identified. Thirty-eight (74 [36-100] years, 42·1% females) patients with AFVI were analysed. Bleeding was reported in 18 (47·4%) patients at diagnosis and in three (7·9%) during follow-up (7 [0·2-48.7] months). At diagnosis, FV was <10% in 31 (81·6%) patients. Bleeding at diagnosis was associated with a prolonged prothrombin time that strongly correlated with the AFVI level measured in plasma {r = 0·63, 95% confidence interval (CI) [0·36-0·80], P < 0·05}. Bleeding onset during follow-up was associated with a slow AFVI clearance (P < 0·001). The corresponding receiver operating characteristics curve showed that AFVI clearance was predictive of bleeding onset with an AFVI clearance of seven months with a sensitivity of 100% (95% CI: 29-100) and a specificity of 86% (95% CI: 57-98, P = 0·02). Kaplan-Meier analysis showed that AFVI clearance >7 months increased the risk of bleeding by 8 (95% CI: [0·67-97], P = 0·075). Prothrombin time at diagnosis and time for clearance of FV inhibitor during follow-up are both associated with bleeding in patients with AFVI.

Factor V activity in apheresis platelets: Implications for management of FV deficiency

BACKGROUND

Allogeneic platelet (PLT) infusion is a strategy to raise Factor V (FV) levels in patients with congenital FV deficiency. However, since FV is labile in vitro, we hypothesized that FV activity could be low in PLT units.

STUDY DESIGN AND METHODS

FV activity was tested using a prothrombin time-based platform in the supernatant and platelet lysate (PL) of apheresis PLT units (16 units stored in PLT additive solution with acetate and phosphate [PAS-C] and 10 units stored in plasma only), on post-collection days 3-6. Statistical analysis was performed using Student's t test (P < .05).

RESULTS

FV activity was severely diminished in PAS-C PLTs (N = 16) supernatant (3.70% ± 1.02%) and PL (3.26% ± 1.02%). FV activity in plasma-only PLTs (N = 10) was lower in both supernatant (44.55% ± 6.46%) and lysate (39.67% ± 6.33%) relative to normal plasma levels, but both were significantly higher (P < .0001) compared to PAS-C PLTs. In a separate set of experiments, FV activity in PAS-C PLTs examined serially over storage time (N = 3 for these experiments) showed that FV levels were reduced by day 3 and not significantly different by day 5 of storage (Day 3 supernatant 5.03% ± 1.41%; Day 5 supernatant: 3.10% ± 0.57%; P = .2; Day 3 lysate: 3.89% ± 1.03%; Day 5 lysate: 2.61% ± 0.41%; P = .4).

CONCLUSION

Plasma should be considered over PLTs as first-line therapy for non-complex FV deficiency-associated hemorrhage. If PLTs are considered for transfusion, plasma-only PLT units should be preferentially utilized, as PAS-C PLT have near-absent FV activity.

Mixing-based inhibitor screening in haemophilia A: challenges in interpretation

: Inhibitor development in haemophilia A patients is a dreaded complication of factor VIII (FVIII) replacement therapy. With increasing use of FVIII replacement therapy, there is an imperative need for cost-effective and standardized screening. To evaluate the efficacy of mixing-based inhibitor screening (MBIS) in the detection of FVIII inhibitors and to assess the best cut-off values for MBIS. Forty inhibitor positive and 40 inhibitor negative haemophilia A patients, diagnosed by standard criteria, with detailed clinical, haematological and on-demand treatment records were included. MBIS was evaluated in all 80 cases and a classical Bethesda assay and Nijmegen modification of Bethesda assay (NBA) were used as gold standards for inhibitor diagnosis. Classical Bethesda assay missed eight cases, most with low titres, which were confirmed by NBA. A systematic analysis of cut-offs for MBIS using a receiver operating characteristic curve fixed the cut-off at more than 5 s. MBIS detected 36 out of 40 inhibitor positive haemophilia A patients with a sensitivity, specificity, PPV and NPV of 90.0, 95, 94.7, 90.5%, respectively, whereas at the conventional cut-off of more than 10 s, MBIS detected only 25 of 40 cases with a low sensitivity of 62.5%. The likelihood ratio of a positive test was 11. The false-negative haemophilia A patients had low titres from 1.6 to 4.2 BU/ml. MBIS at a cut-off of 5 s can be considered as an effective screening test in low-resource situations. In clinical situations and in cases with clinical evidence of inhibitors we recommend that a direct NBA should be done.

A high titer of acquired factor V inhibitor in a hemodialysis patient who developed arterial thrombosis

An 87-year-old man with diabetes mellitus was admitted to control recurrent bleeding from hemodialysis puncture sites. He was a smoker and had been diagnosed with arteriosclerosis obliterans. His PT and APTT were markedly prolonged, and all coagulation factors were markedly decreased (factor V [FV] activity < 1%) or below the measurement threshold, with the exception of fibrinogen and factor XIII. Neither PT nor APTT were corrected upon mixing with normal plasma. A high titer of FV inhibitor was found at 415 BU/mL, and anti-FV autoantibody was detected by both immunoblot assay and ELISA. Prednisolone administration and plasma exchange partially improved prolonged PT and APTT and decreased the FV inhibitor level. Five months later, he manifested symptoms of severe ischemia in both legs. Angiography revealed diffuse stenosis downstream of both common iliac arteries. Endovascular therapy was repeated four times, the prednisolone dose was reduced, and low-dose antiplatelet therapy was initiated. After the final successful endovascular therapy, arterial thrombosis was detected using ultrasound and angiography. Aspiration thrombectomy and thrombolytic therapy failed to achieve recanalization, and necrosis of the legs worsened. Despite the severe coagulation abnormalities, vascular interventions should have been performed with regular-dose antiplatelet therapy, as the patient exhibited multiple risk factors for atherothrombosis.

Acquired factor V deficiency in a patient with a urinary tract infection presenting with haematuria followed by multiple haemorrhages with an extremely low level of factor V inhibitor: a case report and review of the literature

: Acquired factor V deficiency (AFVD) is a rare haemostatic disorder that is primarily because of the development of factor V inhibitors. Approximately, 200 cases have been reported and the greatest portion of these cases was because of bovine thrombin exposure. We report a case of a man who presented with haematuria followed by multiple haemorrhages associated with an elevated prothrombin time and an activated partial thromboplastin time. A workup revealed reduced factor V activity and a factor V inhibitor level of 1.9 BU, which were likely secondary to a urinary tract infection. Using corticosteroids, we successfully eliminated the inhibitor and controlled the bleeding. We review the published literature to identify the conditions that are associated with nonbovine thrombin AFVD. We assume that AFVD should be kept in mind for patients who present with multiple haemorrhages.

Factor V Inhibitors: A Diagnostic and Therapeutic Challenge

Historically, inhibitors to coagulation factor V (FV) most often have developed in patients treated with bovine thrombin, a topical hemostatic agent used during surgical procedures. With the advent of newer hemostatic agents, and the concurrent diminished use of bovine thrombin, the incidence of FV inhibitors has fallen. Nevertheless, FV inhibitors are occasionally seen on an idiopathic basis as well as in association with medications, malignancies, autoimmune disorders, pregnancy, and infections. Factor V inhibitors may present with life-threatening bleeding or thrombosis, or they may be discovered incidentally as a coagulation screening test abnormality. Management of patients with FV inhibitors is challenging and consists of control of bleeding and eradication of the inhibitor. In this short overview we review the role of platelet and plasma FV in hemostasis and discuss the unique characteristics, clinical features, diagnosis, treatment, and prognosis associated with FV inhibitors.

Fatal hemorrhage due to a spontaneous factor V inhibitor with lupus anticoagulant properties

: Factor V inhibitors are rare and have varied clinical presentations. We report on a 76-year-old female admitted to the hospital for pneumonia and treated with multiple antibiotics. Her baseline prothrombin time was 15.6 s and the activated partial thromboplastin time was 35 s. On admission day 10, she developed arm weakness and brain imaging showed a subdural hematoma. The prothrombin time was now 59.1 s with an activated partial thromboplastin time of more than 160 s and a normal thrombin time. A mixing study did not correct the clotting times and coagulation factor assays showed a nonspecific inhibition pattern. Only factor V activity remained low with serial dilutions, however, and a 70 Bethesda Unit inhibitor was identified. Aggressive supportive care was initiated but the patient succumbed to the effects of the intracranial hemorrhage. Factor V inhibitors may display lupus anticoagulant properties and may cause catastrophic bleeding. Our case illustrates that these inhibitors can arise quickly and supports an association with antibiotics.

Pearls and pitfalls in factor inhibitor assays

The proper performance and interpretation of factor inhibitor assays is a critical role for the hemostasis laboratory. Both false-positive and false-negative inhibitor assays may be reported, leading to serious patient mismanagement. Knowledge and recognition of common causes of both false-positive and negative-results can aid in the identification of these potential pitfalls. Safeguards to reporting accurate factor inhibitor assays include initial characterization of the sample, using the Nijmegen modification, properly performing and interpreting an incubated mixing test in conjunction, and performing two dilutions for each dependent dilution in the factor inhibitor assay.

Why Do Patients Bleed?

Patients undergoing surgical procedures can bleed for a variety of reasons. Assuming that the surgical procedure has progressed well and that the surgeon can exclude surgical reasons for the unexpected bleeding, then the bleeding may be due to structural (anatomical) anomalies or disorders, recent drug intake, or disorders of hemostasis, which may be acquired or congenital. The current review aims to provide an overview of reasons that patients bleed in the perioperative setting, and it also provides guidance on how to screen for these conditions, through consideration of appropriate patient history and examination prior to surgical intervention, as well as guidance on investigating and managing the cause of unexpected bleeding.

Acquired factor V inhibitor after exposure to topical human thrombin related to an otorhinolaryngological procedure

Acquired factor V (FV) inhibitors occur rarely and classically develop after exposure to bovine thrombin. The clinical presentation is variable, ranging from asymptomatic with incidental laboratory abnormalities to significant bleeding. With the development of human-derived thrombin agents, bovine thrombin is less frequently used. We report a case of an acquired FV inhibitor that developed in a patient after exposure to human thrombin used as a hemostatic agent during an otorhinolaryngology surgical procedure. Our review of the literature revealed only one prior reported case of FV inhibitor after exposure to human thrombin. Hematologists and surgeons should be aware of this rare, but potentially life-threatening, complication in the postprocedural setting.

Acquired factor v inhibitor developing after treatment with dabigatran etexilate methanesulfonate: a case report and review of the literature

A 90-year-old man presented with subcutaneous ecchymoses. He had been under treatment with dabigatran etexilate methanesulfonate (DEM). Prolonged APTT and decreased PT was developed 2 months after the start of DEM, more prolonged 6 months later. DEM was discontinued, the coagulopathy did not improve. Factor V activity was decreased, along with appearance of coagulation factor V inhibitor (FVI). He did not have antiphospholipid syndrome or malignancy. He was diagnosed as having acquired FVI caused by DEM. Steroid pulse therapy was effective. There have been 74 reported cases of AFVI induced by drug treatment, but none after treatment with DEM.

Acquired factor V inhibitor in a patient with mantle cell lymphoma presenting with hematuria followed by thrombosis: a case report

Acquired factor V inhibitor is a rare hemostatic disorder that presents with hemorrhagic manifestations in the vast majority of patients. Factor V inhibitor may develop through a variety of mechanisms involving development of alloantibodies or autoantibodies specific to Factor V. Autoantibodies, in particular, have been reported in a number of conditions. In this report, we describe a case of acquired factor V inhibitor in a patient with mantle cell lymphoma who presented with hematuria. Seven weeks after diagnosis and successful management, the patient developed deep vein thrombosis in the right lower extremity. The patient’s factor V levels were normalized, and the inhibitor was successfully eradicated using corticosteroids. Here, we discuss this rare disorder, its unusual manifestation, and provide a mini-review of the current literature regarding factor V inhibitors.

Acquired factor V inhibitor in a woman following aortic aneurysm surgery

A 67-year-old woman with nephrotic syndrome as a complication of membranous glomerulonephritis associated with chronic active hepatitis B virus infection developed factor V inhibitor following emergency aortic aneurysm surgery followed by massive blood transfusions and haemodialysis. On the second postoperative day, prothrombin time and activated partial thromboplastin time increased and were unresponsive to fresh frozen plasma. Epistaxis and urethral bleeding were observed, followed by mucosal mouth bleeding. A very low factor V activity less than 5% was found and a factor V inhibitor was detected at 7.76 Bethesda Units. Treatment with corticosteroids was successful. In this patient, several conditions known to predispose to the generation of factor V inhibitor occurred simultaneously. Four months later, factor V inhibitor (225 Bethesda Units) recurred and the patient died of intracerebral haemorrhage.

Bleeding associated with acquired factor V inhibitor in a patient on warfarin treated successfully with prednisolone

An 85-year-old man on warfarin for atrial fibrillation presented with skin bleeding. International normalised ratio (INR) and activated partial thromboplastin time (APTT) were elevated and did not correct even after warfarin reversal with vitamin K, prothrombin complex concentrate (PCC) and fresh frozen plasma. Mixing coagulation studies with normal plasma suggested the presence of an inhibitor rather than the multiple coagulation factor deficiencies expected with warfarin. Assays of the common-pathway coagulation factors revealed factor V concentration <2% with inhibitor level elevated to 11 Bethesda units. The bleeding resolved following a course of corticosteroids. Coagulation studies and factor V level returned to normal along with resolution of the inhibitor. We report the case of the diagnostic dilemma posed and successful therapy implemented despite the limited evidence-based data being available for the treatment of this rare condition.

Nijmegen-Bethesda assay to measure factor VIII inhibitors

Hemophilia A is an inherited bleeding disorder caused by a deficiency of factor VIII coagulant activity (FVIII:C). Patients are treated with infusions of either plasma-derived or recombinant factor VIII. However, some patients develop inhibitory antibodies (inhibitors) to infused factor VIII which render it ineffective. The original Bethesda method was developed to standardize measurement of inhibitors in a factor VIII neutralization assay. One Bethesda unit is defined as that amount of inhibitor that results in 50% residual FVIII:C activity of a defined test mixture. In the Nijmegen modification of the original Bethesda method, the pH and the protein concentration of the test mixture is further standardized. As a result, the FVIII:C in the test mixture is less prone to artifactual deterioration and the test has improved specificity. Even with a standardized procedure a number of factors can affect the performance of the test and it is important for laboratory staff to be aware of their impact on the result outcome.

Successful management of a possible antibiotic-related acquired factor V inhibitor: a case report and review of the literature

Acquired factor inhibitors are rare. We report a case of an elderly male who presented with a bleeding diathesis associated with an elevated prothrombin time and an activated partial thromboplastin time. Work-up revealed undetectable factor V activity and a factor V inhibitor level of >50 Bethesda units. The inhibitor may have been triggered by antibiotics. With a multimodality approach using steroids, platelet transfusions, intravenous immunoglobulin, factor VIII inhibitor bypass activity agent and cyclophosphamide, we successfully eliminated the inhibitor and controlled the bleeding.

Acquired factor V inhibitor developing in a patient with esophageal squamous cell carcinoma

An 82-year-old man referred to our medical ward because of epistaxis and melena was found to have 12 Bethesda units of factor V inhibitor. He was managed for bleeding with supportive care, followed by corticosteroid therapy. The bleeding completely stopped 1 week after corticosteroid therapy. Medical history revealed dysphagia during the past 6 months and further evaluation brought to light a squamous cell carcinoma (SCC) in the esophagus. This is the first case of an acquired factor V inhibitor developing in a patient with esophageal SCC without any other risk factors such as surgery.

Laboratory identification of factor inhibitors: an update

Coagulation factor inhibitors comprise antibodies that bind to and then neutralise specific pro-coagulant plasma proteins. Coagulation factor inhibitors can develop against any coagulation factor, although the most common are against factor VIII (FVIII). These can develop in individuals with inherited haemophilia A (HA) as an immune response to factor replacement therapy, or as auto-antibodies leading to the condition of acquired HA. Clinical suspicion for inhibitors may arise when individuals present with bleeding symptoms without any prior bleeding diathesis, or when a patient with known mild haemophilia presents with a bleeding diathesis more extreme to their usual presentation, or when there is failure of factor replacement therapy to arrest bleeding in a known haemophiliac. The laboratory identification of factor inhibitors requires a careful and systematic approach that excludes other possible causes of prolonged screening tests, most commonly the activated partial thromboplastin time (APTT), and sometimes prothrombin time (PT). Coagulation factor inhibitor studies, including the Bethesda assay, are then undertaken to measure inhibitor titre, which guides treatment. This paper overviews the laboratory investigation of factor inhibitors, and also briefly reviews recent cross-laboratory inhibitor studies and the most recent evidence related to differential inhibitor formation according to type of therapy.

A rare case of factor V inhibitor in a patient on amiodarone therapy

Factor V inhibitor is in itself a rare entity. We are reporting a case of an elderly male who presented with symptoms of bleeding and was later found to have developed factor V inhibitors. He had been on amiodarone for atrial fibrillation and developed hemorrhagic manifestations due to factor V inhibitors within a few months of initiating amiodarone therapy. Most of the cases of factor V inhibitors reported in the literature were found to be associated with exposure to bovine coagulation factors. However, in our case there was no evidence of bovine thrombin use during surgery. Furthermore, bovine thrombin-associated factor V inhibitors commonly emerge within 1-2 weeks after exposure during surgery versus several months later in our patient. There was dramatic improvement in the coagulation profile 6 weeks after discontinuation of amiodarone and institution of steroids and cyclophosphamide. We propose the consideration of amiodarone as a contributing agent in inhibitor generation even though a spontaneous development of factor V inhibitor could not be ruled out.

Acquired factor V inhibitors: a systematic review

The occurrence of an inhibitor against coagulation factor V (FV) is a rare but challenging condition, which may span from asymptomatic laboratory abnormalities to potentially life-threatening bleeding. The onset of FV inhibitors has been associated most frequently in the past with the patients' exposure to topical bovine thrombin administered during surgery procedures. However, since this preparation is no longer used, in this systematic review we have only focused on non-bovine thrombin-related FV inhibitor cases.

Postoperative acquired coagulopathy: a pilot study to determine the impact on clinical and economic outcomes

STUDY OBJECTIVE

To characterize the clinical factors associated with postoperative acquired coagulopathy, and to estimate the economic impact of resources used to treat postoperative patients with this coagulopathy compared with postoperative patients who did not develop the coagulopathy.

DESIGN

Case-control study.

SETTING

Academically affiliated public hospital and level I trauma referral center.

PATIENTS

Twenty-six patients (mean age 53.9 yrs) who experienced acquired coagulopathy after undergoing an index surgery (cases), and 26 patients (mean age 50.8 yrs) matched to these case patients by index surgery, age, and sex (controls).

MEASUREMENTS AND MAIN RESULTS

Data were collected from a database of 5367 adult surgical admissions over 6 months during 2008, corresponding inpatient electronic health records, billing data, and Medicare Resource-Based Relative Value Scale payments. Case patients had a minimum of two postoperative consecutively drawn episodes of prothrombin time (PT) or activated partial thromboplastin time (aPTT) elevated to greater than 20% above the upper limit of normal. Patients with inherited clotting disorders or other identifiable causes of coagulopathy were excluded. Case patients underwent the following surgeries: 12 orthopedic (46%), six cardiovascular (23%), four gastrointestinal (15%), and four neurosurgical (15%). Mean values of the first elevated PT and aPTT were 19.7 and 50.8 seconds, respectively. Mean postoperative stay was 31.5 days for cases versus 9.8 days for controls (p<0.05). Mean cost (2008 U.S. dollars) of resources used was $112,280 for cases versus $38,357 for controls (p<0.001). Costs incurred between the onset of coagulopathy and discharge constituted 67% of postoperative costs. Physician reimbursement expenditures were minimal.

CONCLUSION

Postoperative acquired coagulopathy was associated with stays that were 3 times longer and resource use costs that were 3 times higher than those of controls. This type of coagulopathy may be an under-recognized and underappreciated event. The case-control design is limited to exploring associations and does not establish causality. Prospective studies need to be conducted to establish the causes of acquired coagulopathy and methods for screening and diagnosing this condition.

Acquired factor V inhibitor in a critically ill patient

Acquired inhibitor of factor V is a rare condition with a variety of clinical manifestations, from extremely mild to life threatening haemorrhage. We present a case from our intensive care unit as a reminder of the less common causes of elevated prothombin and activated partial thromboplastin times, and how knowledge of the variable presentation may aid management.