Anticoagulants, Circulating |
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Circulating anticoagulants are abnormal blood components that inhibit coagulation. They are usually discovered by an abnormal coagulation test such as the activated partial thromboplastin time (APTT).
The presence of an anticoagulant can be confirmed by performing a 1:1 mix of patient and normal plasma and repeating the APTT immediately and after one hour's incubation of the mixture. Ten to 20% normal plasma is usually sufficient to replace a deficient factor and normalize the APTT. If the patient's abnormal APTT is corrected by normal plasma, this indicates that a deficient clotting factor has been supplied and a coagulation factor deficiency exists. If the 1:1 mix has a prolonged APTT immediately, this means that an immediate-acting circulating anticoagulant (such as heparin) is present. If the initial clotting time of the 1:1 mix corrects partially or fully, but is definitely prolonged after incubation, this suggests a time dependent anticoagulant, which progressively inactivates a clotting factor (such as a Factor VIII inhibitor).
Specimen requirement is one 4.5 mL blue top (sodium citrate) tube
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