title: The factor V Leiden mutation: spectrum of thrombotic events and laboratory evaluation.
abstract: OBJECTIVE
  This study aims to describe the spectrum of clinical thrombotic events and to compare the methods of laboratory evaluation for the newly described prothrombotic factor V Leiden mutation.
  
  
  METHODS
  Specimens from 1376 patients with thrombotic events or their relatives were tested for the factor V Leiden mutation by polymerase chain reaction plus restriction digest from Jan. 1, 1995, to Mar. 31, 1996. Activated protein C (APC) resistance test data was available for 554 of these patients. Clinical information was available for 166 patients with the mutation.
  
  
  RESULTS
  Of 1376 patients tested for factor V Leiden mutation, 270 (19.6%) were positive, with 12 homozygotes and 258 heterozygotes. Of 554 patients for whom APC resistance data was available, 221 (39.9%) had low APC resistance ratios (< or = 2.4); of these only 97 (43.9%) were factor V Leiden-positive. Among 333 samples with normal or elevated APC resistance ratios, 19 (5.7%) were later identified with the factor V Leiden mutation, despite the normal screening test. One hundred fourteen of 166 patients (68.7%) with the mutation had at least one thrombotic event, most commonly deep venous thrombosis and pulmonary embolus. Arterial cerebrovascular thrombotic events occurred in 11 patients (10%), and myocardial infarctions in eight (7%). The mean age of all patients with arterial thrombotic events was 45.4 years.
  
  
  CONCLUSIONS
  The factor V mutation is a common cause of venous thromboses but may also be associated with the early presentation of arterial thrombotic events. The APC resistance test is a sensitive screening assay but has limitations of its specificity in clinical practice.
authors.affiliation: Division of Hematology, University of Pittsburgh School of Medicine, PA 15213, USA.
authors.forename: F A
authors.initials: FA
authors.lastname: Bontempo
authors.forename: A C
authors.initials: AC
authors.lastname: Hassett
authors.forename: H
authors.initials: H
authors.lastname: Faruki
authors.forename: D L
authors.initials: DL
authors.lastname: Steed
authors.forename: M W
authors.initials: MW
authors.lastname: Webster
authors.forename: M S
authors.initials: MS
authors.lastname: Makaroun
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D005165:Factor V / Q000235:genetics*; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D002542:Intracranial Embolism and Thrombosis / Q000097:blood / Q000235:genetics; D008875:Middle Aged; D009203:Myocardial Infarction / Q000097:blood / Q000235:genetics; D010314:Partial Thromboplastin Time; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D011486:Protein C / Q000378:metabolism; D011655:Pulmonary Embolism / Q000097:blood / Q000235:genetics; D013924:Thrombophlebitis / Q000097:blood / Q000235:genetics; D013927:Thrombosis / Q000097:blood / Q000235:genetics*
chemical_list: D011486:Protein C; C095381:factor V Leiden; D005165:Factor V