i've not heard that the pt/inr not be done early in the day. i know that coumadin, the anticoagulant, which these tests assess the effectiveness of, should be given in the late afternoons. the reason has to do with the amount of time between the administrations of the medication, the blood levels of the anticoagulant, and the time the blood specimen is going to be taken. if the coumadin is given in the morning, then the pt/inr will need to be drawn in the late afternoon to avoid getting an inaccurate reading.
a embolus is a blood clot. initial coagulation studies may show that the patient has some sort of physiological problem with the natural clotting mechanisms that is causing blood clots to form in his/her body. however, upon discovering a pulmonary embolus, the standard medical treatment is to start the patient on anticoagulation therapy as soon as possible to prevent the embolus from becoming larger and prevent the formation of more emboli. these drugs are monitored by the coagulation studies and inr. their doses are titrated according to the lab data provided by pt/ptt and inr tests. when a patient is started on heparin, it is not usual for the doctor to have a ptt drawn every 4 hours until an adequate therapeutic anticoagulation response is seen in the labwork.
your question gets asked a lot. here are a number of old threads about these lab tests. within one or two of these threads are links to lab tests online where you will find explanations about each of the coagulation lab tests.
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