Factor V inhibitors

Topical bovine thrombin and adverse events: a review of the literature

OBJECTIVE

To review published evidence suggesting a link between topical bovine thrombin (TBT) and important adverse events (AEs).

RESEARCH DESIGN AND METHODS

English language articles and abstracts were obtained from MEDLINE using combinations of text and MeSH terms for thrombin, bovine thrombin and their trade names. References from summary articles were also retrieved. Published case reports, review articles, and retrospective, prospective or observational studies involving either immunogenicity or AEs were selected for further assessment. Retrieved articles were evaluated separately as AE case reports, quantitative studies of antibodies, or quantitative studies of AEs.

MAIN OUTCOME MEASURES

Presence of case causal information, temporal pattern of case report publication, reproducibility of aggregate data findings, and study design features.

RESULTS

The major limitations of reviewed publications were insufficient information regarding TBT and other exposures, and designs in which linkage between laboratory immune phenomena and AEs could not be evaluated. While immunogenicity studies did support an increased risk for post-TBT antibodies, there was no consistent evidence that this led to an increased AE risk or severity. Common evidentiary deficiencies included case reports from high incidence environments, studies of combination or mixture products, biased study designs, lack of patient-level exposure data, inadequate control groups and insufficient sample sizes. The best designed study (a randomized, controlled comparison of TBT to a recombinant bovine product) documented post-TBT antibody production, but no important efficacy or AE differences. An examination of publication dates for case reports showed a peak between 1992 and 1994 followed by a substantial drop. Since 1997 the number of published AE case reports has continued to decline.

CONCLUSIONS

TBT increases the risk for antibody elevations in patients. A careful review of published evidence does not show that either TBT itself or any associated elevations in anti-bovine antibodies are risk factors for clinically important AEs.

Successful treatment with rituximab in a patient with an acquired factor V inhibitor

Rituximab has already been successfully used to treat immune-mediated bleeding disorders such as acquired factor VIII inhibitor. We report here a case of severe acquired factor V (FV) inhibitor deficiency due to FV inhibitor which has been dramatically improved after rituximab.

Factor V inhibitor: case report

Acquired inhibitors to coagulation factors are rare, certainly those directed against factor V. A total of around 150 cases have so far been reported, of which the greater part was due to bovine thrombin exposure. We report the case of a patient who developed a factor V inhibitor during a postoperative period. This report describes possible aetiologies, varying clinical conditions and treatment possibilities as described in the literature. Furthermore, this case report is an example of the often unpredictable disease progression in a patient with existence of a factor V inhibitor.

Mis-identification of factor inhibitors by diagnostic haemostasis laboratories: recognition of pitfalls and elucidation of strategies. A follow up to a large multicentre evaluation

AIMS

We previously reported the ability of diagnostic haemostasis facilities to identify coagulation factor abnormalities and inhibitors, through a large multi-centre study conducted on behalf of the Royal College of Pathologists of Australasia (RCPA) Quality Assurance Program (QAP). In the current report, additional data evaluation aims to (1) help identify the reasons behind the failures in inhibitor identification, (2) highlight the pitfalls in inhibitor testing, and (3) help elucidate some strategies for overcoming these problems and to assist in better identification and characterisation of inhibitors.

METHODS

Forty-two laboratories blind tested a set of eight samples for the presence or absence of inhibitors. These included true factor inhibitors (FVIII and FV), and other samples that reflected potential pre-analytical variables (e.g., heparin contamination, serum, EDTA plasma, aged plasma) that might arise and complicate inhibitor detection or lead to false inhibitor identification.

RESULTS

There was a wide scatter of inhibitor results, with false positive and false negative inhibitor identification, and mis-identification of inhibitors (e.g., FVIII inhibitor identified where FV inhibitor present). Further analysis of the pattern of reported laboratory results, including routine coagulation testing and factor profiles, allowed some additional interpretative power to provide strategies that will assist laboratories to improve the accuracy of inhibitor identification in the future.

CONCLUSIONS

There are currently occasional lapses in factor inhibitor identification, which this report will hopefully help address.

Acquired factor V inhibitor responsive to corticosteroids in a patient with double cancers

A 70-year-old woman suffering from HCV-related liver cirrhosis was admitted for abnormal bleeding. Laboratory findings included PT at 46.6 sec, APTT at >212 sec, factor V activity of <3%, and factor V inhibitor of 2 BU. Having experienced a persistent bleeding tendency for one month, the patient was started on prednisolone (0.8 mg/kg/day). Within a few days, the inhibitor became undetectable and clinical bleeding disappeared. Although clinical improvement was achieved, she died 6 months after the initial bleeding episode from the progression of a lung cancer. An autopsy revealed squamous cell carcinoma of the lung and hepatocellular carcinoma.