title: Protein C and protein S levels can be accurately determined within 24 hours of diagnosis of acute venous thromboembolism.
abstract: In the 50% of cases of acute idiopathic venous thromboembolism, laboratory testing for inherited causes is often performed. Most physicians are under the impression that assays for protein C and protein S should not be measured at the time of diagnosis because of a high false positive rate. We performed a prospective cohort study from two outpatient thromboembolism clinics on consecutive patients with an objectively confirmed diagnosis of first acute idiopathic venous thromboembolism. Assays for protein C and protein S were performed prior to the initiation of oral anticoagulation therapy and within 24 h of diagnosis of venous thromboembolism. Abnormal results were repeated when patients discontinued oral anticoagulant therapy. Of 253 patients tested for both protein C and protein S, 229 (91%; 95% confidence interval 87-94%) were negative and 484 of 508 (95%) tests were normal. Of the 24 initial abnormal results, 21 were repeated and 10 (48%; 95% confidence interval 26-70%) were still abnormal. Overall, 97.8% of initial protein C and protein S results were accurate. If protein C and protein S are measured at the time of diagnosis of acute venous thromboembolism, the majority of the results will be normal and false positives are uncommon.
authors.affiliation: Department of Medicine, London Health Sciences Centre, London, ON, Canada. michael.kovacs@lhsc.on.ca
authors.forename: M J
authors.initials: MJ
authors.lastname: Kovacs
authors.forename: J
authors.initials: J
authors.lastname: Kovacs
authors.forename: J
authors.initials: J
authors.lastname: Anderson
authors.forename: M A
authors.initials: MA
authors.lastname: Rodger
authors.forename: K
authors.initials: K
authors.lastname: Mackinnon
authors.forename: P S
authors.initials: PS
authors.lastname: Wells
mesh_terms: D000208:Acute Disease; D000284:Administration, Oral; D000293:Adolescent; D000328:Adult; D000925:Anticoagulants / Q000008:administration & dosage; D001780:Blood Coagulation Tests / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D011446:Prospective Studies; D011486:Protein C / Q000032:analysis*; D017293:Protein S / Q000032:analysis*; D015203:Reproducibility of Results; D013923:Thromboembolism / Q000097:blood* / Q000175:diagnosis / Q000188:drug therapy; D013997:Time Factors
chemical_list: D000925:Anticoagulants; D011486:Protein C; D017293:Protein S