Is it necessary to fast when checking blood coagulation function? What should I pay attention to?

Author: Cui Wei, Researcher at the Cancer Hospital of the Chinese Academy of Medical Sciences

Reviewer: Duan Yanlong, Chief Physician, Beijing Children's Hospital, Capital Medical University

We all have this experience in life: when we accidentally cut our hands, we bleed, and after a while the bleeding stops.

1. Why does the skin solidify after a while after being scratched?

The process of hemostasis seems simple, but in fact, a series of reactions occur in the body. Professionally speaking, the process of hemostasis is divided into two parts, the first part is primary hemostasis, and the second part is secondary hemostasis.

Who is responsible for primary hemostasis? Usually, it is the blood vessels and platelets. Bleeding occurs because of damage to the blood vessels. At this time, the blood vessels will first begin to contract, which will shrink the wound, slowing down the local blood flow. At this time, the platelets can adhere to the wound and aggregate to form a small platelet thrombus, sealing the damaged blood vessels, thus achieving the effect of primary hemostasis.

Although the first stage of hemostasis has done a certain job, the platelet thrombus formed is not stable. In order to prevent bleeding again, the coagulation factors in the body will be activated at the same time. After a series of complex coagulation pathways, thrombin is finally activated, which makes the soluble fibrinogen become insoluble fibrin. These filamentous fibrins are wrapped around the platelet thrombus, making the thrombus more stable. This step is called the second stage of hemostasis.

Figure 1 Original copyright image, no permission to reprint

After the primary and secondary hemostasis, the local blood vessel damage is truly stabilized and blocked, and the bleeding stops. So we can see that a small wound, from bleeding to hemostasis, actually undergoes a lot of internal reactions.

2. How to check whether the coagulation function is normal?

During the coagulation process, it activates two systems in the body, one is the coagulation and anticoagulation system, and the second is the fibrinolysis and antifibrinolysis system.

For these systems, some indicators are tested clinically, such as prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT), fibrinogen content (FIB), D-dimer (D-Dimer) and fibrinogen degradation product (FDP), which are what we often call the six coagulation items.

Sometimes some hospitals will also check the four coagulation items, excluding FDP and D-Dimer, which are the routine tests of PT, APTT, TT and FIB.

Figure 2 Original copyright image, no permission to reprint

3. When drawing blood to check coagulation function, do I need to fast or stop taking anticoagulants?

Generally speaking, it is recommended to do coagulation function tests on an empty stomach as much as possible. Why?

Because there may be more lipid particles in the blood when blood is drawn after a meal, which will affect the test results of coagulation function, it is recommended to draw blood for coagulation function test on an empty stomach to minimize the influence of lipid particles. Especially for patients who already have elevated blood lipids, fasting blood is more necessary for testing.

Whether to stop taking anticoagulants before blood collection depends on the situation. For patients who take anticoagulants for a long time, when performing coagulation function tests, we may see that their coagulation time is prolonged. Depending on the different medications taken, it may manifest as abnormalities in different coagulation items, such as prolongation of PT, APTT or TT. If this patient undergoes surgery without stopping anticoagulants, intraoperative and postoperative bleeding is prone to occur. If this patient does not stop taking anticoagulants and blood is drawn for coagulation function testing, it may cause the doctor to misjudge his coagulation function status.

Therefore, for patients who need surgery, it is recommended to inform the doctor of the anticoagulant situation in a timely manner, stop taking anticoagulants as ordered by the doctor, and then do a coagulation function test. This will help the doctor judge his true coagulation function and decide his next treatment plan.

However, there is also a situation where the coagulation function test is used to monitor the anticoagulant effect of anticoagulants to see whether the choice of drugs and the dosage are reasonable. At this time, there is no need to stop the drug, because what needs to be understood at this time is the coagulation function state of the drug when it reaches a stable state in the body. If the coagulation time is prolonged, it may be an overdose of the drug. If the coagulation time is too short, it may be an underdose of the drug, which prompts the clinician to make reasonable adjustments to the medication.

4. Could frequent nosebleeds be a sign of a problem with blood coagulation?

From a clinical perspective, nosebleeds caused by the body's coagulation dysfunction are a very common phenomenon. For example, patients with leukemia may experience epistaxis, which is the phenomenon of nosebleeds.

However, in some cases, nosebleeds may have little to do with the body's overall coagulation dysfunction. For example, patients with congenital nasal septum deflection, nasal structural changes, and allergic rhinitis may also experience frequent nosebleeds.