Activated Protein C-Resistance Determination and Vascular Access Thrombosis in Populations with High Prevalence of Factor V Leiden.

BACKGROUND/AIMS: Factor V Leiden heterozygosity occurs in 3-8% of the general European and US populations. Activated protein C resistance (APC-R)--a non-molecular laboratory test--can efficiently demonstrate the presence of this mutation and can be performed on most coagulation analyzers. On the other hand, fistula or graft thrombosis is a common and costly complication in hemodialysis patients. Our aim was to establish the value of APC-R determination in hemodialysis patients by assessing the risk of access thrombosis in patients with increased APC-R. METHODS: A total of 133 patients (81 men, mean age 64.5 ± 14.9 years and 52 women, mean age 63.6 ± 15 years) were selected. Participants were divided into 2 groups: those with access thrombosis (54 patients, 40.6%) and those with no access thrombosis (79 patients, 59.4%), and they were tested for the most common congenital or acquired thrombophilia risk factors. RESULTS: Overall, 12 patients (9%) had an increased APC-R and 10 of them had at least 1 episode of access thrombosis (83.3%). Univariate analysis to estimate crude odds ratio (OR) showed an OR of 8.8 (95% CI 1.8-41.8) times higher risk for access thrombosis in these patients. No significant differences were found after adjusting for age, hypertension, diabetes mellitus, coronary artery disease, cerebrovascular disease, peripheral arterial disease and malignancy. Sex was also a factor influencing thrombosis, presenting a higher OR for women (OR 2.2, 95% CI 1.1-4.4). CONCLUSION: This study revealed a significant association between access thrombosis and increased APC-R in hemodialysis patients. This indicates that the determination of APC-R should be considered--especially, in populations with a high prevalence of Factor V Leiden--as proper anticoagulant therapy in these patients may reduce the risk of access thrombosis.

Screening with the activated protein C resistance assay yields significant savings in a patient population with low prevalence of factor V leiden.

Testing for factor V Leiden can be performed with a molecular assay or a test for activated protein C resistance. We noted that physicians in our institution tended to order the molecular test 80% of the time, but the prevalence of the mutation in our patient population was less than 10%. Consequently, we decided to introduce the activated protein C resistance assay in house and consistently use it for screening before the more expensive genetic test and to negotiate a discounted charge for the latter at a reference laboratory. After 6 years since these interventions began, the prevalence of an abnormal screening test result remained low (202/2,475 [8.2%]), even among white patients (10.9%). With this simple approach, the cost to test patients for factor V Leiden decreased by more than 90%, while the productivity of our laboratory increased by the introduction of a high-volume, fully automated assay.

Screening for activated protein C resistance before oral contraceptive treatment: a pilot study.

The feasibility and cost-effectiveness of screening women for congenital thrombophilic alterations before oral contraceptive (OC) treatment was investigated. A total of 525 women (mean age 21.9 years, 73% aged < 25 years) were examined before their first OC course. At first screening, completely normal results were recorded in 485 (92.4%) women, the remaining showing single (n = 34) or multiple (n = 6) alterations. At second examination (possible in 37 of 40), activated protein C resistance (APCR) was confirmed in 21 cases (4.0%, 18 with factor V Leiden), protein C, or protein S reduction in 8 (1.5%) and 2 (0.4%) cases, respectively. No cases with antithrombin III deficiency were detected. The global estimated cost ($US) to detect one altered case was: $7795 for protein S, $2696 for antithrombin III (no case found), $1374 for protein C and $433 for APCR. The present study confirms that extensive thrombophilic screening before OC treatment is not currently advisable. APCR assessment, however, seems to have a favorable cost-effectiveness ratio: the alteration is frequent and has a synergistic effect with OC; sensibility and specificity of some methods are good; family history is unreliable to single out possible carriers; finally, carriers can be fully informed of their increased thrombotic risk if treated with OC and can receive thromboprophylaxis during life situations associated with high thrombotic risk (e.g., pregnancy and puerperium).

PIP: This article investigates the feasibility and cost effectiveness of screening women for congenital thrombophilic changes before oral contraceptive (OC) treatment. The study population included 525 women who were examined before their first OC course between September 1995 and May 1997 in Bologna, Italy. A completely normal result was seen in 92.4% women during the first screening, which was conducted before the first OC course. The second examination showed that activated protein C resistance (APCR) was confirmed in 21 cases (4.0%, 18 with factor V Leiden), and protein C and protein S reduction in 8 (1.5%) and 2 (0.4%) cases, respectively. Antithrombin III deficiency cases were not detected. The detection of one altered case is estimated to cost $7795 for protein S, $2696 for antithrombin III, $1374 for protein C, and $433 for APCR. The study confirmed that extensive thrombophilic screening before OC treatment was not advisable. However, APCR assessment was found to be cost-effective. The alteration was frequent and APCR had a synergistic effect with OC, and the sensibility and specificity of some methods for detection of APCR are good. Family history is not reliable for identifying possible carriers for the thrombophilic trait. Carriers can be fully informed of their high risk if treated with OC and can receive thromboprophylaxis in conditions where thrombotic risk is high.