Diagnostic Issues of Thrombophilia

Several congenital and acquired abnormalities of the hemostasis system have been identified that increase the risk for thromboembolic diseases. These conditions are collectively referred to as a state of thrombophilia. A clinical impression of a potential state of thrombophilia is usually followed up by a request for laboratory tests that should confirm or rule out such defects. At present, these tests are not always reliable and these problems are the subject of this issue of Seminars in Thrombosis and Hemostasis. The clinician who manages these patients has to be aware of the potential shortcomings of some of the tests and will have to take these issues into consideration.

In the first article, Mannucci presents a historical perspective on inherited states of thrombophilia. The first defect to be reported was antithrombin deficiency, but this defect is rather rare. All patients so far identified are heterozygotes; homozygosity appears to be incompatible with life. Next, defects in protein C and protein S were discovered. These are more common than antithrombin defects, but still are relatively rare. Much more prevalent, at least in white patients, is resistance to activated protein C; in most cases, this is due to a molecular defect in the factor V molecule. This is known as factor V Leiden. Almost as frequent is a gene mutation in the prothrombin molecule. At present, these two defects account for the majority of congenital thrombophilic states. There are additional ones, but they are relatively uncommon. The author discusses the laboratory approaches and delineates who should be tested for hypercoagulability.

In the next article, Favaloro discusses the issue of laboratory testing for thrombophilic states. Many conditions can be assayed for, but many issues remain to be resolved. Questions, such as who should be tested, when patients and their family members should be tested, what is the meaning and the consequences of positive test results, and what are the consequences of negative test results, still need to be answered. The author expresses concern about the ever-growing requests for laboratory tests and the uncertainty of how the test results are interpreted by the healthcare providers. It is also suggested that consensus opinions have to be reached, and that greater emphasis needs to be placed on education.

Galli and Barbui review the issues related to the antiphospholipid syndrome, including laboratory testing and clinical significance. Work during the last 10 years has elucidated the effects of antiphospholipid antibodies on the hemostasis system and their possible role in thrombus formation. However, many problems remain regarding laboratory testing of both lupus anticoagulant and anticardiolipin antibodies. Tests need to be standardized and their specificity has to be improved. The authors conducted an extensive literature search on the clinical relevance of antiphospholipid antibodies and found that, without doubt, the presence of the lupus anticoagulant presents a strong risk factor for arterial and venous thrombosis. Unless the G isotype is present, anticardiolipin antibodies do not present a risk. The association between anti-β₂-glycoprotein I antibodies and thrombosis is less certain and no definite conclusions could be reached. Antiprothrombin antibodies appear not to present a risk. The authors see the need for well-designed clinical trials with standardized laboratory procedures to form meaningful conclusions.

Tripodi reviews the clinical and diagnostic utility of laboratory tests for detecting congenital thrombophilic states. Once again, the issue of who and when to test is briefly addressed. The author then comprehensively describes the laboratory tests available to determine defects in antithrombin, protein C, protein S, and activated protein C resistance (APCR). Activity measurements, antigen determinations, and DNA analyses, where applicable, are described; problems with the assay systems are identified and their strengths and weaknesses are discussed. This review provides the reader with a comprehensive and practical laboratory approach to congenital thrombophilia.

Hertzberg comprehensively discusses genetic testing for thrombophilia mutations. Of the known congenital hemostasis defects related to inhibitors, only factor V Leiden and the prothrombin G20210A mutation are prevalent in the white population. Both convey an increased risk of thromboembolism to the carriers. Controversy exists, however, as to who should be tested and the consequences of such studies. In addition, the methylenetetrahydrofolate reductase (MTHFR) mutation and other factor V mutations can be identified by genetic testing. The author discusses the test systems presently in use and elucidates their advantages and disadvantages. This article is helpful to readers who must decide about the clinical importance of genetic testing.

Wong and coworkers discuss the issues related to laboratory testing of anticardiolipin antibodies and lupus anticoagulant. The problems associated with these assay systems, especially their lack of specificity, are well recognized in the scientific community. Many groups of investigators and members of professional organizations have wrestled with the concept of developing consensus guidelines and recommended procedural aspects that should be followed by laboratories that offer these tests. The authors provide details of these efforts, and despite of the best intentions by many, the current guidelines are still not optimal. Continued efforts have to be put forth to improve the testing for these important risk factors of thromboembolism.

Favaloro and coworkers describe the results of a quality assurance program related to thrombophilia testing. Known normal and abnormal plasma samples were tested by 84 laboratories located primarily in Australia, New Zealand, and Southeast Asia for defects in antithrombin, protein C, protein S, APCR, and lupus anticoagulant. A diagnostic error rate of 2 to 10% was observed for these analytes that was dependent on the tests and the methods employed. Most consistent results were obtained when antithrombin was determined, and the greatest variability was noted for protein S. Protein C assays were influenced by the presence of APCR. Although it is clear that improvements are needed, the overall data are encouraging.

Meijer and Haverkate describe their experience with an external international quality assessment of laboratory tests for thrombophilia conducted in Europe. About 400 laboratories participate, and antithrombin, protein C, protein S, and APCR are the analytes. The program not only assesses performance between laboratories, but also measures performance over a prolonged period of time. Test samples include normal, borderline, and abnormal plasmas. Analysis of between-laboratory results revealed significant differences in antithrombin and protein S levels. Less problematic were protein S and APCR testing. Long-term analyses were even more discrepant. The data once again suggest that caution must be exercised when interpreting laboratory test results that relate to thrombophilia testing.

Jennings and coworkers report the results of a National Quality Assessment Program conducted in the United Kingdom, which involves screening tests for thrombophilia. Plasmas of patients with protein C, protein S, and antithrombin defects, and with factor V Leiden were tested on several occasions by 280 centers. Overall, 21% of the laboratories reported incorrect diagnoses. Failings by individual laboratories related to methods used, reagents used, and inappropriate reference ranges. In many instances identification of the problems and repeat testing corrected the errors. The authors stress that well-designed external quality assessment schemes, discussions with the laboratories, and dissemination of the data greatly improved laboratory performance.

Favaloro and associates describe the results of a multilaboratory peer-assessment quality assurance program for the evaluation of anticardiolipin and β₂-glycoprotein I antibodies. The study, conducted in 2002, involved 56 laboratories and 12 samples. As reported by others as well, high interlaboratory variations were found that, to some extent, were based on different methodologies. In addition, interpretation of laboratory data was highly variable. The authors caution that laboratory results should never be used in isolation to diagnose the antiphospholipid syndrome or antiphospholipid syndrome-like disorders. They also express not only the need for improvements in standardization of the assays, but also in worldwide quality assurance programs.

Favaloro next summarizes the quality assessment programs related to thrombophilia testing and once again reiterates the importance of these activities. Of the anticoagulant factors, the defects of which relate to thrombophilia, antithrombin, and protein C assay methods give the most encouraging results. Protein S assays still present a major problem and determinations of APCR are also not optimal at this time. Major difficulties exist with assays of lupus anticoagulant, anticardiolipin, and β₂-glycoprotein I antibodies. Rigorous quality assurance programs and standards are needed to improve the clinical interpretation of thrombophilia-related tests.

Gallus discusses the issue of travel and thromboembolic diseases. It has been suggested that long-distance travel, especially in airplanes, might precipitate venous thrombosis and potentially pulmonary embolism. There is reasonable evidence that this is true, and long-haul travel (i.e., longer than 12 hours), appears to increase the risk. Although there is no evidence that this phenomenon is linked to economy-class travel, there are data that support the assumption that acquired and congenital thrombophilic states may be involved. Hormonal therapy and congenital problems such as factor V Leiden may be important factors. No specific prophylactic measures can be recommended at this time (an exception may be support stockings), and larger studies are needed to ultimately address this issue.

Hoffman and Brenner review the issue of thrombophilia in women and in children. It is well established that pre-eclampsia, intrauterine growth retardation, and abruptio placentae are related to the hemostasis system, and acquired and congenital thrombophilic states all increase the risk markedly. They also enhance the risk for fetal loss and intrauterine fetal death. This is especially true for patients with the factor V Leiden and prothrombin mutations, hyperhomocysteinemia, and combined defects. In addition, the risk for pregnancy-related venous thromboembolism is increased by the presence of thrombophilic states. Finally, oral contraception and hormone replacement therapy, when complicated by thromboembolism, increase the risks. The authors comprehensively review the details of these associations.

Falanga next reviews thrombophilia in cancer patients. Cancer is an acquired state of thrombophilia that is triggered by a variety of mechanisms, in essence related to the tumors. Clinically, this hypercoagulable state can manifest itself from a silent thrombosis to disseminated intravascular coagulation. Inter-relationships between coagulation and inflammation, tumor growth, and metastasis are well recognized. The author also addresses the therapeutic consequences, from prophylaxis to the actual management of cancer-related thromboembolism.

Allman-Farinelli and Dawson examine the role of diet and aging on thrombosis and hemostasis. There is considerable evidence that changes in protein, carbohydrate, and fat intake may influence the risk of thromboembolism through alterations in platelet function (aggregation), clotting factors, and the fibrinolytic system. In addition, the B vitamins influence thrombosis by mediating homocysteine metabolism. Hyperhomocysteinemia is a well-recognized risk factor for thrombosis. Aging increases the risk for thrombosis as well, and physiological factors, such as malnutrition and lack of mobility, and psychological factors all appear to play a role. Another factor in older persons is the multitude of medications that are frequently ingested. More studies are needed to further our knowledge in this important area.

In the last article, Gallus discusses the management of thromboembolism as a consequence of acquired or congenital thrombophilia. The author also addresses the issue of laboratory testing for thrombophilia. Clearly, unfractionated and low molecular weight heparins (UFHs and LMWHs, respectively) are the initial treatment for thromboembolism, followed by oral anticoagulation. LMWHs have gained preference because of their better and safer pharmacological profile. In particular, cancer patients seem to benefit from LMWHs. The target value for control of oral anticoagulants (international normalized ratio, 2.0 to 3.0) is generally agreed upon, but the length of treatment may vary. The type of thrombophilia (congenital or acquired), severity and recurrence of thrombosis, and family history all have to be considered. At present, there is no clear consensus on these issues, but the author extensively reviews the available data. Generally, there appears to be no need for life-long anticoagulation for most patients with thrombophilia, but exceptions exist. In addition, screening of patients and their family members for thrombophilic states is not recommended. It serves, with rare exceptions, no clinical purpose. The author cautions, however, that today's conclusions and recommendations may be obsolete tomorrow.

I would like to thank all of the authors for their valuable contributions and Dr. Favaloro for assembling this important issue. It is hoped that readers will have a better appreciation of the complexities of thrombophilia, especially as they relate to laboratory testing.