APC-RESISTANCE AS MEASURED BY A TEXTARIN TIME ASSAY: COMPARISON TO THE APTT-BASED METHOD
Section snippets
Blood Collection, Preparation and Storage
Blood was collected in evacuated tubes (Vacutainer Systems®, Becton Dickinson, Rutherford, New Jersey) containing 0.5 ml of 0.105M buffered sodium citrate. Platelet poor plasma (PPP) was prepared by centrifugation at 2000 g for 10 min. in a 4°C centrifuge. The PPP supernatant was then transferred to a 5 ml polypropylene tube using a plastic transfer pipette and recentrifuged under the same conditions. The final PPP product was transferred to another 5 ml polypropylene tube and tested within 4
Oral Anticoagulated Samples
After determining the reference intervals as described in the previous section, seventeen stable oral anticoagulated samples were tested in both test systems for comparison. The patient INRs ranged from 1.3 to 4.0. Of these seventeen patients, two tested positive for APC resistance (ratio <2.0) in both test systems. (Table 1) These patients were then confirmed to be heterozygous factor V Leiden using Polymerase Chain Reaction (PCR) [11].
Previously Diagnosed Factor V Leiden Samples
Fourteen samples from patients who had been previously
DISCUSSION
Since the discovery of APC-Resistance as a major cause of venous thrombosis, laboratories have routinely implemented tests to identify these patients. The most popular test system employs the original assay as described by Dahlback and colleagues utilizing an APTT system [1]. However, other test systems have been utilized including: a dilute Russell Viper Venom Time, a modified prothrombin time (one-stage tissue factor-dependent factor V assay), a protein C activation dependent clotting time
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