Detection of the factor VLeiden mutation. Development of a testing algorithm combining a coagulation assay and molecular diagnosis

A 9-year retrospective assessment of laboratory testing for activated protein C resistance: evolution of a novel approach to thrombophilia investigations

AIMS

To assess international and local trends in laboratory testing for activated protein C (APC) resistance (APCR) and factor V Leiden (FVL). Also, to compare local results of FVL testing with a variety of different clot-based APCR assays to assess utility for detection of APCR both related and unrelated to FVL.

METHODS

Local test statistics and test result patterns were evaluated and international literature was reviewed over the past 9 years. Direct comparisons of FVL testing by DNA analysis against (a) the standard APTT-based APCR assay, with and without pre-dilution with factor V deficient (FVD) plasma, or with and without normalisation, and (b) three alternative RVVT-based procedures (most recently using a commercial RVVT-based procedure called GradiLeiden V; GLV). In total, data obtained over the past 7 years, using referred samples from over 1,000 patients, have been assessed.

RESULTS

The 9-year retrospective assessment has seen many changes in test-based processes. Locally, test requests for both APCR and FVL have consistently increased. We suspect this has been fuelled in part by media reports of 'economy class syndrome' (ECS) and associated general public and clinical concern. Current request patterns number around 800 APCR and 1,600 FVL per year. Interestingly, most requests are for one or either test, with joint requests comprising less than 20% of those overall. Although test requests are increasing, detection of the FVL defect as a proportion of test requests is actually falling (from a high of over 25% in 1996 to around 14% currently). Whether this suggests an increasing tendency for clinical ordering in the absence of appropriate clinical histories is a matter of concern. Consistent with previous findings, the original and commonly used APTT-based procedure was found to show the least correlation with DNA findings, with a large overlap between FVL and non-FVL individuals. The alternate-RVVT-based procedures showed much better differentiation. Thus, for the APTT-based method, in order to ensure 100% sensitivity, an APC ratio cut-off value of 3.1 was required, and this yielded only 49.1% specificity. In contrast, for the GLV RVVT-based method, in order to ensure 100% sensitivity, an APC ratio cut-off value of 1.65 was required, and this yielded 96.6% specificity.

CONCLUSIONS

It is important to recognise the limitation of APTT-based assays to discriminate FVL. However, a combination of RVVT- and APTT-based testing is still recommended, as this will provide excellent discriminatory power for the FVL defect, particularly negative prediction, in addition to detection of potential APCR unrelated to FVL, as well as detection of other potential haemostatic disturbances. Accordingly, we detail strategies, including a test algorithm that we are currently using to improve our detection of APCR and prediction of FVL, and use of clotting-based procedures as the first-line approach.

Diagnostic testing for coagulopathies in patients with ischemic stroke

BACKGROUND

Hypercoagulable states are a recognized, albeit uncommon, etiology of ischemic stroke. It is unclear how often the results of specialized coagulation tests affect management. Using data compiled from a systematic review of available studies, we employed quantitative methodology to assess the diagnostic yield of coagulation tests for identification of coagulopathies in ischemic stroke patients.

SUMMARY OF REVIEW

We performed a MEDLINE search to identify controlled studies published during 1966-1999 that reported the prevalence of deficiencies of protein C, protein S, antithrombin III, plasminogen, activated protein C resistance (APCR)/factor V Leiden mutation (FVL), anticardiolipin antibodies (ACL), or lupus anticoagulant (LA) in patients with ischemic stroke. The cumulative prevalence rates (pretest probabilities) and positive likelihood ratios for all studies and for those including only patients aged </=50 years were used to calculate posttest probabilities for each coagulopathy, reflecting diagnostic yield. The cumulative pretest probabilities of coagulation defects in ischemic stroke patients are as follows: LA, 3% (8% for those aged </=50 years); ACL, 17% (21% for those aged </=50 years); APCR/FVL, 7% (11% for those aged </=50 years); and prothrombin mutation, 4.5% (5.7% for those aged </=50 years). The posttest probabilities of ACL, LA, and APCR increased with increasing pretest probability, the specificity of the tests, and features of the patients' history and clinical presentation.

CONCLUSIONS

The pretest probabilities of coagulation defects in ischemic stroke patients are low. The diagnostic yield of coagulation tests may be increased by using tests with the highest specificities and by targeting patients with clinical or historical features that increase pretest probability. Consideration of these data might lead to more rational ordering of tests and an associated cost savings.

Genetic determinants of heritable venous thrombosis: genotyping methods for factor V(Leiden)A1691G, methylenetetrahydrofolate reductase C677T, prothrombin G20210A mutation, and algorithms for venous thrombosis investigations

OBJECTIVES

To implement cost effective and clinically relevant thrombophilic genotyping and homocysteine analysis in our coagulation laboratory.

METHODS

We describe genotyping assays for three of the genetic defects associated with hereditary thrombosis: factor V(Leiden) A1691G, methylenetetrahydrofolate reductase C677T, and prothrombin gene G20210A. A second confirmatory assay for factor V(Leiden) using allele specific oligonucleotide polymerase chain reaction is also presented. We suggest an algorithm for the rational integration of the traditional assays routinely used to investigate venous thrombosis with genotyping and plasma homocysteine measurements.

RESULTS

These polymerase chain reaction based assays were designed to be performed under identical reaction conditions, permitting simultaneous setup, amplification, digestion, and analysis.

CONCLUSIONS

The three genotyping assays presented are robust and relatively easy to perform. Use of an algorithm will ensure efficient resource utilization and minimize unnecessary testing.

The role of activated protein C resistance in the pathogenesis of venous thrombosis

Venous thromboembolism (VTE) is the third most common cardiovascular disease in the United States. VTE is usually a consequence of either acquired or inherited alterations in hemostatic regulatory proteins. These regulatory proteins are predominantly those of the protein C/protein S natural anticoagulant pathway. Acquired deficiencies in this pathway are frequently a consequence of other clinical entities (eg, cancer, AIDS, and diabetes), while inherited deficiencies can be responsible for venous thrombosis in an otherwise healthy individual. The purpose of this article is to briefly describe the pathobiology of the anticoagulant protein system and to review the clinical implications of activated protein C resistance.