A New Dilution for the Modified APTT-based Assay for Activated Protein C Resistance: Improvement of the Reliability in Patients with a Lupus Anticoagulant

Laboratory Diagnosis of Activated Protein C Resistance and Factor V Leiden

The factor V Leiden (FVL) polymorphism is known as the most common inherited risk factor for venous thrombosis. In turn, FVL is the leading cause of an activated protein C resistance (APCR) phenotype, in which the addition of exogenous activated protein C to plasma does not result in the expected anticoagulant effect. In the routine laboratory approach to the formal diagnosis of FVL, an initial positive screening plasma-based method for APCR is often performed, and only if needed, this is followed by a confirmatory DNA-based assay for FVL. Multiple methods with accepted sensitivity and specificity for determining an APCR/FVL phenotype are commonly categorized into two separate groups: (1) screening plasma-based assays, including qualitative functional clot-based assays, for APCR, and (2) confirmatory DNA-based molecular assays, entailing several tests and platforms, including polymerase chain reaction-based and non-PCR-based techniques, for FVL. This review will describe the methodological aspects of each laboratory test and prepare suggestions on the indication of APCR and FVL testing and method selection.

The Predictability of Factor V Leiden (FV:Q506) Gene Mutation via Clotting-Based Diagnosis of Activated Protein C Resistance

After the discovery of activated protein C resistance (APCR) due to factor V Leiden mutation and the causal relationship of the phenomenon with clinical thromboembolism, a wide variety of functional clotting-based assays were developed for testing of APCR in relation to the specific DNA-based analysis of FV:Q506 Leiden. The aim of this study is to assess a clotting-based APCR assay using procoagulant crotalidae snake venom with respect to the sensitivity, specificity, and predictability for the presence of the factor V Leiden mutation. APCR testing and factor V DNA analyses have been performed concurrently on 319 patient specimens. APCR values of the patients with homozygous factor V Leiden mutation (70.4±13.5 s) were significantly lower (p<0.001) in comparison to the subjects with the heterozygous mutation (87.6±13.4 s). The assay is highly sensitive (98.7%) and specific (91.9%) for the screening of factor V Leiden mutation. The sensitivity and specificity of the APCR testing reached to 100% below the cut-off value of 120 s among the patients with homozygous factor V Leiden mutation. Therefore, this method could help the desired effective optimal screening strategy for the laboratory search of hereditary thrombophilia focusing on the diagnosis of APCR due to FV:Q506.

Membrane autoantibodies in systemic lupus erythematosus: a case of autoimmune hemolytic anemia, antiphospholipid antibodies, and transient acquired activated protein C resistance

BACKGROUND

Warm autoimmune hemolytic anemia and antiphospholipid antibodies (which include lupus anticoagulants and anticardiolipin [ACL] antibodies) are associated, respectively, with approximately 10 and 40 percent of cases of systemic lupus erythematosus (SLE). This study reports a case of SLE presenting with an unusual constellation of findings that included an immunoglobulin M (IgM) cold autoantibody of high thermal amplitude, high-titer ACL antibodies, and transient acquired activated protein C resistance.

CASE REPORT

A previously untransfused, nulligravid 17-year-old woman without a significant medical history presented with signs and symptoms of SLE and an extravascular hemolytic anemia. Spontaneous agglutination was noted in blood samples collected for testing. Serologic testing revealed a normal-titer, high-thermal-amplitude IgM red blood cell (RBC) autoantibody but no additional RBC antibodies in the patient's plasma. Additional testing was significant for a high-titer ACL IgM and a positive test for activated protein C resistance (a screening test for the Factor [F]V Leiden mutation), which prompted initiation of prophylactic anticoagulation. Confirmatory DNA testing for FV Leiden, however, was negative. The patient's symptoms, anemia, RBC autoagglutinins, ACL antibodies, and activated protein C resistance all resolved after 6 weeks of immunosuppression.

CONCLUSION

This case illustrates the wide range of clinical and laboratory findings that autoantibodies against cellular membranes may produce. IgM autoagglutinins of high thermal amplitude associated with a significant extravascular hemolytic anemia may be a presenting feature of SLE. Concomitant antiphospholipid antibodies may interfere with partial thromboplastin time-based tests of hypercoagulability such as that for activated protein C resistance.

A 2-year retrospective analysis of laboratory testing for activated protein C resistance with a factor V-corrected activated partial thromboplastin time-based method

The factor V-corrected activated protein C resistance assay is the test of choice to screen for the factor V Leiden mutation. During the past 2 years, local test results with the frequently used Coatest APCR kit were evaluated and compared with the results of DNA analysis, the 'gold standard'. Samples of 278 patients were analysed by both techniques. We were unable to confirm that factor V Leiden carriers can clearly be delineated from normal individuals with the Coatest APCR test. A ratio of 2.0 as the cut-off provides 99.0% sensitivity and 95.4% specificity.To evaluate the lupus anticoagulant interference, we retrospectively analysed 16 lupus anticoagulant-positive patients. In this study, two (12.5%) showed a false-positive activated protein C resistance result. Six out of 16 (37.5%) lupus anticoagulant-positive patients were also carriers of the factor V Leiden mutation. Four out of eight (50%) false-positive activated protein C resistance results presented with an abnormal baseline clotting time. In order to prevent reporting false-positive results, a maximum baseline clotting time (65.8 s) was calculated. A new scheme for interpreting activated protein C resistance ratios was proposed.

Activated protein C resistance, the factor V Leiden mutation, and a laboratory testing algorithm

OBJECTIVES

To present the current understanding of factor V Leiden and activated protein C resistance, and to propose a laboratory testing algorithm.

DATA SOURCES

Publications on MEDLINE with the terms factor V Leiden or activated protein C resistance through mid 2001, as well as publications in the authors' files, were screened for inclusion in this report.

STUDY SELECTION

Original studies that report a novel finding on testing or clinical features of activated protein C resistance or factor V Leiden are included. Data Extraction.-The novel or key findings from the selected studies are analyzed.

DATA SYNTHESIS

Protein C and protein S are the integral components of an anticoagulation pathway that limits fibrinogen conversion to fibrin through the degradation of factors Va and VIIIa. When factor Va is resistant to degradation by activated protein C, this anticoagulation pathway does not operate properly, and patients have an increased risk for thrombosis. This report describes the protein C/protein S pathway, the significance of activated protein C resistance and the factor V Leiden mutation, and the clinical testing used to detect activated protein C resistance and the factor V Leiden mutation. A proposed laboratory testing algorithm is also provided.

CONCLUSIONS

Factor V Leiden is a risk factor for venous thrombosis and it is particularly common in white populations. A laboratory testing algorithm is proposed.