Laboratory Referral Rates of Genetic Tests for Thrombophilia Workup in a Major Referral Center

Introduction

The blood coagulation system is a balanced regulatory system that encloses several plasma clotting factors and aids in responding to injury through developing a series of chemical reactions that lead to fibrin formation (Jadaon et al., 2010). A defect in this system originating from a deficiency in natural anticoagulants or from other factors including surgery, long distance travel, oral contraceptives, and obesity may result in a continuous uncontrolled coagulation process known as hypercoagulability or thrombosis (Yokus et al., 2009). Inherited thrombophilia is a multiple gene disease resulting in increased risk of thrombosis due to one or several genetic defects (Larciprete et al., 2010). Thrombophilia manifests clinically as various conditions including venous thromboembolism (VTE) leading to cardiovascular diseases and pulmonary embolism, stroke, and some complications in pregnancies such as early and late pregnancy loss, preeclampsia, intrauterine growth restriction, and placental abruption (Zahed et al., 2006; Kosar et al., 2011). It has been reported that VTE occurs in 1 to 5 people per 1000 annually, and almost 1% of women experience recurrent pregnancy loss (Lund et al., 2010; Tug et al., 2011).

The most common gene mutations involved in inherited thrombophilia are Factor V Leiden mutation (FVL, G1691A), methylenetetrahydrofolate reductase mutation (MTHFR, C677T), and prothrombin gene mutation (F2, G20210A) (Rahimi et al., 2010). The prevalence of these mutations varies among different populations where the FVL variant is frequently found among Europeans, Canadians, and Indians (1%-8.5%) but rare or absent in Africans, Japanese, and South East Asians (<1%) (Ayadurai et al., 2009; Hussein et al., 2010). In the East Mediterranean countries, the prevalence of FVL is considered the highest, for instance, almost 14% to 15% of the Lebanese population carry this mutation (Finan et al., 2002). The F2 G20210A mutation is found worldwide with an approximate prevalence of 2% (Mazoyer et al., 2009). In Lebanon, the prevalence of this mutation does not differ much from the rest of the world; it is found in 1%-3% of healthy individuals (Sabbagh et al., 2009). The MTHFR C677T mutation is detected in 5% to 20% of the European population and is rarely found among Asians and Africans. The Lebanese healthy population carries the MTHFR C677T variant in the homozygous and heterozygous states with a prevalence of 11.0% and 39.7%, respectively (Zahed et al., 2006).

Inherited thrombophilia causes complications in various surgeries including orthopedic, vascular, and cardiac surgery and in kidney and pancreas transplantation; therefore, it is important to perform a thrombophilia workup among patients undergoing any of these procedures (Kfoury et al., 2009). In addition, the FVL mutation was found in increased frequency among patients with sickle-beta zero thalassemia, and some of these patients experience severe thrombotic events. This implicates the necessity of the thrombophilia screening in these patients in order to avoid any undesired complication (Isma'eel et al., 2006a). Surprisingly, FVL was associated with increased sperm counts leading to a higher chance of establishing a pregnancy; however, this involves an increased possibility of spreading the mutated genotype (Cohn et al., 2010).

It is important for the physicians to identify the reason behind the thrombotic events occurring in their patients and to differentiate whether these events are provoked (due to immobility, use of contraceptives, and obesity) or spontaneous (due to a certain or several mutations), in order to make an appropriate decision concerning the treatment (Isma'eel et al., 2006b). Family history of thrombotic events and the prevalence of the FV, F2, and MTHFR mutations in the ethnic group and society to which the patient belongs should also be taken into consideration when deciding on the priority of thrombophilia workup (Yokus et al., 2009).

In our study, the frequency of requesting the thrombophilia test was determined among the medical and surgical specialties and within each subspecialty in order to assess the rate of referrals among each category. This is the first report of its kind in the region as well as, to our knowledge, in the international literature that addresses this subject.

Materials and Methods

Results

As per Figure 1, referrals from medical and surgical specialties were almost equal (51.86% and 48.14% respectively). In the surgical specialty, most referrals came from the department of obstetrics and gynecology (76.11%) followed by vascular surgery (16.33%). The remaining subspecialties, neurosurgery, general surgery, and orthopedic surgery, contributed to 2.74%, 1.7%, and 1.42% of the referrals, respectively. As for the medical specialty, most of the workup referrals originated from the internal medicine department (78.61%) and more specifically, from the hematology/oncology physicians (43.5% of the internal medicine specialty). In addition, 14.11%, 5.35%, and 1.3% of the referrals were from the pediatrics, family medicine, and emergency medicine departments, respectively.

OPEN IN VIEWER

FIG. 1.

The distribution of factor V, prothrombin, and methylenetetrahydrofolate reductase referrals among various medical and surgical specialties.

Table 1 represents the genetic mutation positivity rate among total and specialty-specific referrals defined as heterozygous or homozygous for Factor V Leiden or Factor II, or homozygous for MTHFR (since heterozygous for MTHFR has not been shown to be associated with predisposition for thrombosis). From all referred cases, 42.23% turned out to be classified as positive for a genetic mutation in the thrombophilia genes.

Discussion

Thrombotic events can occur due to several acquired factors including surgery, long duration immobilization, pregnancy, antiphospholipid syndrome, obesity, and the use of contraceptives (Hussein et al., 2010). Inherited thrombophilia results from molecular abnormalities in some components of the coagulation system including factor V, prothrombin, and MTHFR, and the prevalence of the mutations affecting the genes encoding these factors differs between various ethnic groups (Otrock et al., 2008). Thrombophilia workup, especially for FVL, G20210A, and MTHFR C677T mutations, is essential among Lebanese patients experiencing thrombotic events and among healthy individuals, as the prevalence of these mutations in Lebanon is considered of the highest as described in the medical literature.

The highest referral per surgical specialty pertains to the obstetrics/gynecology department because of the workup of recurrent abortions or multiple failures of in vitro fertilization where our medical center has one of the most busy fertility centers in the country. The vascular surgery team referrals come second and mainly for the workup of deep vein thrombosis.

As for the medical specialties, the hematology/oncology team referrals rank first in terms of having their hematology and coagulation experts consulted on any referred case for thrombosis or coagulopathy. The neurology team ranks second in the medical referrals for inherited thrombophilia workup, especially for stroke related to vascular thrombosis.

The interesting and surprising finding comes from the low referral rates by the emergency and family medicine practitioners probably because of the current system of patient workup in our institution and medical culture in general. Patients screened by family or emergency practitioners tend to be referred for final workup by the expert thrombosis/coagulopathy teams, most likely, immediately after admission of these cases to the hospital for clinical or surgical management. Therefore, it could have been possible that these physicians have ordered these tests on initial assessment of the cases, but according to our search strategy in this report, only the names of the “admitting” physician were utilized for building up of the analysis.

Among all referrals, a 42.23% positivity rate for harboring a mutation that has been reported to be associated with predisposition to thrombosis is considered high and, thus, at least in our country, alerts all practitioners that genetic testing for thrombophilia workup should be a routinely available test for this patient population.

In conclusion, this is the first report in our country as well as in the international literature that tackles the issue of patient referral rates for inherited thrombophilia workup among different medical and surgical specialties. This is extremely useful and important to discuss and follow, especially in Lebanon, where the community harbors one of the highest prevalences of Factor V, Factor II, and MTHFR gene mutations in the world. In addition, we highly encourage all diagnostic laboratories to have the genetic profile for this category of patients as a part of their routine offered tests.