Diagnosis of fibrinogen deficiency, both congenital and acquired, as well as screen for dysfibrinogenemia.6 Normal values for reptilase time when thrombin time is prolonged suggests the presence of heparin or a direct thrombin inhibitor.
Reptilase is a thrombin-like enzyme. Unlike thrombin, which cleaves fibrinogen to produce fibrinopeptides A and B, reptilase cleaves the fibrinogen molecule to release only fibrinopeptide A.6,7 Reptilase time may be more sensitive than a thrombin time to the presence of a dysfibrinogenemia. The reptilase clotting time may be used in place of, or in conjunction with, the thrombin time to measure fibrin formation. Both reptilase time and thrombin time will be extended when functional fibrinogen levels are <100 mg/dL.6,7 This can occur due to congenital conditions, including afibrinogenemia (complete lack of fibrinogen), hypofibrinogenemia, and in dysfibrinogenemia, a condition characterized by the presence of dysfunctional fibrinogen. Acquired conditions that can lead to diminished fibrinogen levels and extended reptilase times include liver disease, renal disease, disseminated intravascular coagulation (DIC), amyloidosis, malignancy, and thrombolytic therapy.6 Paraproteins and fibrin degradation products, especially fragments D and E, interfere in fibrin polymerization, thus prolonging both the thrombin time and reptilase time. Bovine thrombin inhibitors (antibovine thrombin antibody) may develop in patients previously treated with “fibrin glue” during surgical procedures (most fibrin glue products contain bovine thrombin). This acquired inhibitor prolongs the (bovine-derived reagent) thrombin time, but does not prolong the reptilase time. A thrombin time using human-derived thrombin reagent will not be prolonged in the presence of a bovine thrombin inhibitor. Unlike thrombin, reptilase is not affected by the presence of heparin, heparinoids, or hirudin and may be a useful tool in evaluating test plasma for their presence.6 A prolonged thrombin time in a patient with a normal reptilase time suggest heparin therapy or contamination.
Blue-top (sodium citrate) tube
Ideally, the patient should not be on anticoagulant therapy. Avoid warfarin (Coumadin®) therapy for two weeks prior to the test and heparin, direct Xa, and thrombin inhibitor therapies for about three days prior to testing. Do not draw from an arm with a heparin lock or heparinized catheter.
Citrated plasma samples should be collected by double centrifugation. Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate.1 Evacuated collection tubes must be filled to completion to ensure a proper blood to anticoagulant ratio.2,3 The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. A discard tube is not required prior to collection of coagulation samples, except when using a winged blood collection device (ie, “butterfly”), in which case a discard tube should be used.4,5 When noncitrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes. Any tube containing an alternate anticoagulant should be collected after the blue-top tube. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes. Centrifuge for 10 minutes and carefully remove 2/3 of the plasma using a plastic transfer pipette, being careful not to disturb the cells. Deliver to a plastic transport tube, cap, and recentrifuge for 10 minutes. Use a second plastic pipette to remove the plasma, staying clear of the platelets at the bottom of the tube. Transfer the plasma into a transpak frozen purple tube with screw cap. Freeze immediately and maintain frozen until tested.
Severe hemolysis; improper labeling; clotted specimen; specimen diluted with IV fluids; samples thawed in transit; improper sample type; sample out of stability
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