Thrombophilia Testing Panel Now Available
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Thrombophilia Testing Panel Now Available Bronson Laboratory offers a any impact on the patient’s therapy. Importantly, most people with an thrombophilia testing panel consisting For instance, the vast majority of older inheritable thrombophilic mutation will of the following: factor VIII activity, anti- patients with venous thromboses in the never experience a thrombotic event, thrombin III activity, protein setting of a recognized inciting event and most of those who do will never C activity, protein S antigen, factor V Leiden will not have a preexisting thrombophilic do so again. Because of this, screening mutation assay, prothrombin 90210A condition, and accordingly testing is the general population or even asympto- mutation assay, and a lupus anticoagulant generally not recommended in this pop- matic relatives of individuals with thrombo- assay. Abnormal values for protein C, ulation. In regards to arterial thromboses, philic mutations is discouraged because protein S, and antithrombin III will be the overwhelming majority are a direct of the potential for harmful overtreatment. automatically reflexed to confirmatory consequence of atherosclerosis, and the By similar reasoning, some hematologists testing at the Mayo Clinic laboratories. added presence of a thrombophilia in would recommend the same period of Although these tests are orderable indi- this setting will not affect patient anticoagulation, often 3-6 months after vidually, there is little rationale to do so management. (continued on page 4) except as noted below. Clinical circumstances that suggest The activity assays are clotting tests a laboratory evaluation for thrombophilia that require adequate amounts of func- tional protein to achieve a normal result. For reasons having to do with greater achievable precision, the free protein S Patient with a Asymptomatic patients Other clinical situations with a family history of VTE antigen test is used in lieu of an activity confirmed acute VTE assay, but it too depends on adequate amounts of circulating protein for a normal finding. Importantly, abnormal Only selected patients from the above clinical circumstances values for these tests may indicate either should undergo a laboratory evaluation for thrombophilia an acquired or inherited condition. The mutational assays, on the other hand, directly assess whether a patient has an Selected patients should be Testing should be considered Testing is recommended inheritable deficiency of these factors, considered for thrombophilia in the following situations: only in limited situations: and whether the mutation is homo- testing if at least one of the • Women who intend to • Woman with a history of zygous or heterozygous. As such, they following is present: become pregnant and/or pregnancy loss that is either need only be run once in a patient’s • “Spontaneous” thrombosis use oral contraceptives recurrent or late in pregnancy lifetime. The lupus anticoagulant test (unprovoked) in patients and who have symptom- (second or third trimester) involves two clot-based assays, the aPTT <50 years of age atic first-degree relatives • Woman with a thrombotic with AT, PC or PS event during pregnancy, and dRVVT, as screening tests to exclude • Recurrent venous thrombosis (at any age) deficiency, or FVL HRT, or while taking oral antiphospholipid syndrome. Normal clotting contraceptives • First-degree relatives with VTE times for both of these assays essentially • Thrombosis in unusual sites, such • Patients clinically suspected excludes a lupus anticoagulant. A pro- as portal, mesenteric, splenic, of having APS longed aPTT will reflex to additional hepatic, renal, or cerebral veins testing that includes mixing studies (without a risk factor) to exclude a factor deficiency or drug effect as the cause of the prolongation. An abnormal dRVVT will prompt repeat Physical exam and complete medical history testing with an excess of phospholipid to evaluate for presence of acquired risk reagent to adsorb any antiphospholipid factors for thrombosis (see text) antibody, which should lead to correction of the dRVVT if a lupus anticoagulant is present. Two positive lupus anticoagulant Thrombophilia – High Priority Tests tests separated by at least 12 weeks in The best time to evaluate a patient for an inherited thrombophilia is in the outpatient setting after the acute thrombotic episode has resolved and the patient is no longer acutely ill. the proper clinical setting are necessary If thrombophilia testing must be done during a thrombotic event or anticoagulation, a number for a diagnosis of phospholipid syndrome. of assays may be affected depending on the patient’s condition and the drug used. The syndrome may alternatively be diagnosed by demonstrating IgG or IgM 1. Global coagulation tests: PT, PTT, TT 5. PC activity anticardiolipin or beta 2-glycoprotein 2. Factor V Leiden mutation 6. PS assay 3. Prothrombin G20210A mutation (P20210) 7. Factor VIII activity antibodies, which are tests sent out to 4. AT activity 8. Antiphospholipid antibodies a reference lab. Integral to the effective use of the Figure 1: Outline of the clinical circumstances that suggest a thrombophilia laboratory testing panel is an accurate assessment evaluation and the high priority screening tests. APS, antiphospholipid syndrome; of the likelihood of a thrombophilic AT, antithrombin; FVL, factor V Leiden; HRT, hormone replacement therapy; LA, state in a given patient, and whether the lupus anticoagulant; PC, protein C; PS, protein S; PT, prothrombin time; PTT, presence of a thrombophilia will have partial thromboplastin time; TT, thrombin time; VTE, venous thromboembolism. Thrombophilia Testing Panel Now Available (continued) (continued from page 3) a single episode more common factor V Leiden and References: of venous thrombosis and lifetime anti- prothrombin mutations are unaffected coagulation after a second event, regard- by acute thrombosis or war farin. One College of American Pathologists less of the presence or absence of an reasonable testing strategy might there- Consensus conference XXXVI:Diagnostic inherited thrombophilia. fore be to order the factor V Leiden and Issues in Thrombophilia. Arch Path Lab prothrombin mutational assays in the Med 2002;126:1277-1433. Although there remains some con- hospital and defer the other tests until troversy regarding whom to test, the later. Less ideally, one could order a full Ballard, RB and Marques, MB. Pathology XXXVI College of American Pathologists thrombophilia panel during the initial Consultation on the Laboratory Consensus Conference offers helpful hospitalization, and if the fibrinolytic Evaluation of Thrombophilia. Am J Clin guidance in this regard, and the reader factors are indeed abnormal and a Path 2012;137:553-560. is encouraged to consult this detailed genetic deficiency is a serious concern, but very readable document. Their rec- then follow-up or confirmatory testing Kottke-Marchant, K. (Ed.) An Algorithmic ommendations, issued in 2002, but still for these factors could be performed at Approach to Hemostasis Testing. widely used, are evidence-based and a later date, again after warfarin Northfield, IL:College of American reflect broad expert consensus. Figure 1 discontinuation. Pathologists, 2008. summarizes their guidelines for thrombo- philia testing. An important and guiding It is important to remember that there concept is that the risk of thrombosis are many acquired causes of protein C increases incrementally with each inher- and protein S deficiency besides warfarin, ited or acquired risk factor present, and and that together these will greatly that in most cases abnormal thrombosis outnumber the genetic deficiencies. is only triggered when at least two such Liver dysfunction, vitamin K deficiency, factors coexist in the same patient. L-asparaginase therapy, and DIC can all Thus for instance, if a woman plans to cause deficiencies of both proteins, as become pregnant or use oral contracep- can the aforementioned acute thrombosis. tives (1 thrombosis risk factor) and has a In addition to these causes, protein S symptomatic first-degree relative with an (but not C) deficiency may be seen with inherited thrombophilia (strong possibility pregnancy, estrogen therapy, nephrotic of a 2nd risk factor) then thrombophilia syndrome, and the acute phase state. testing should be considered. Because Acquired antithrombin III deficiency may of the principle of additive incremental be seen in the nephrotic syndrome, risk, if the clinical data on a given patient fulminant hepatic failure/end-stage liver suggest that it is beneficial to assay disease, and DIC. L-asparaginase therapy for the presence of one thrombophilic and unfractionated heparin infusions abnormality, then all inheritable and may also produce a deficiency. acquired possibilities should be assessed. In summary, thrombophilia testing This forms the rational basis for ordering should be reserved for selected patients a panel of tests when thrombophilia whose management plan hinges upon testing is desired. knowing whether they have an inheritable If such testing is deemed appropriate or acquired thrombophilic state. in a particular patient, the next impor- Established guidelines for testing and/or tant consideration is when to perform a hematology consult should ideally be the testing. In general, the evaluation is sought before testing. best performed after an acute throm- Thoughtful interpretation botic event has resolved and the patient of the results is then has been off warfarin therapy for