Why are the tubes used to draw blood colorful? Why do we have to draw so much blood during every physical examination?

Audit expert: Jin Tao

Chief Physician of Hematology Department, Shenyang Red Cross Hospital

When you feel unwell, you usually go to the hospital for a blood test first. It is scary enough to watch the doctor use a small blood collection needle to prick the vein, and the bright red blood flows out of the blood collection needle into the blood collection tube. However, the doctor sometimes takes out blood collection tubes of various colors, one after another... Why do they need to draw so many tubes? And they are in tubes of different colors? Will drawing so much blood cause anemia?

To know the reason behind the colorful blood collection tubes, you must first understand the composition of blood.

Blood is a mixture of plasma and blood cells. The red blood cells, white blood cells and platelets we know are all blood cells. They flow in blood vessels because of the plasma. Plasma itself is also a mixture of proteins, lipids, inorganic salts, sugars, amino acids, metabolic wastes and water. The content of these substances can reflect our physical condition.

When doing blood tests in hospitals, different blood components need to be focused on for different test items. Therefore, adding different substances to different blood collection tubes can facilitate the separation of different blood components and the protection of the substances to be tested. In order to distinguish different additives, the caps of blood collection tubes used for blood drawing are made of different colors, which makes it easier for blood collection nurses to quickly draw blood without having to read the text instructions on the label every time.

Now that we know why blood collection tubes are made in different colors, let’s talk about what the different colors of blood collection tubes represent. (The following colors are domestic standards, and there is no universal standard internationally)

Purple blood collection tube

Contains EDTA anticoagulant to prevent blood clotting and provide non-clotting whole blood specimens for clinical testing. Purple cap tubes are used for testing blood routine, C-reactive protein in cases of cold, fever, anemia, and blood type testing during blood transfusion.

Red blood collection tube

Without adding any ingredients, the blood can coagulate naturally to produce serum specimens. Red cap tubes are used when testing liver and kidney function, cardiac markers, antibodies related to infectious diseases such as viral hepatitis, AIDS and syphilis.

Yellow blood collection tube

It contains coagulants and separation gel, which can reliably separate serum and blood clots without affecting each other, and is used to preserve serum specimens for a long time.

Blue blood collection tube

Contains 1:9 sodium citrate, is an anticoagulant tube, and provides plasma specimens. It is used when platelet and coagulation function need to be tested after taking aspirin, warfarin, etc.

In addition to the above, there are black blood collection tubes, also called erythrocyte sedimentation tubes, which contain 1:4 sodium citrate and are used for erythrocyte sedimentation testing; green blood collection tubes contain heparin and are used for blood viscosity and trace element testing; gray blood collection tubes, also called blood sugar tubes, contain sodium fluoride and are used for blood sugar testing.

Will drawing too much blood lead to anemia? How should people who are afraid of blood take the test? After understanding the uses of different colored blood collection tubes, some people may worry whether drawing blood one tube after another will lead to anemia?

The answer is: No.

There are certain standards for anemia. Anemia is a condition in which the volume of red blood cells in the human body decreases and is lower than the normal range. Among them, adult male hemoglobin concentrations <120 g/L, adult female (non-pregnant) <110 g/L, and pregnant women <100 g/L can be considered anemia. The main symptoms are pale complexion, fatigue, dizziness, increased heart rate, lack of concentration, decreased physical endurance, etc. The more severe the anemia, the more obvious the symptoms.

my country's blood donation standards stipulate that an adult can donate 200-400 ml of blood at a time, which means that normal adult blood loss is safe within this range. In general blood tests, the blood volume is 2-20 ml, and such a small amount of blood loss has no effect on the human body.

Even so, why do some people suddenly feel dizzy, chest tightness, trembling, nausea, cold sweats, or even faint when watching the blood flow from the needle hole into the tube? This is because the person being tested has "hemophobia", which is similar to "acrophobia" and is caused by an overreaction of the autonomic nervous system.

So, how should people who are afraid of blood be tested?

1. Tell your doctor in advance

Some blood drawing rooms have reminders posted at the door to inform medical staff in advance that you are afraid of blood, and they will try to shorten the blood drawing time.

2. Do not look directly at the blood drawing process

Turn your head to the side or close your eyes while your blood is being drawn to distract yourself from the procedure.

3. You can lie flat on your back

When sitting, the tension of the lower limb muscles and veins is low, and the amount of blood returning to the heart is small, which affects the blood supply to the brain. You can lie flat and relax your body.

4. Keep your breathing smooth

If you faint due to blood loss, immediately go to a well-ventilated place to breathe fresh air or breathe oxygen directly, or you can drink some sugar water.

5. Prepare yourself mentally

In most cases, phobia of blood is a psychological effect. Try to overcome your inner fear and relax your mind. If necessary, you can ask family and friends to accompany you to bring psychological comfort.

Friends who are afraid of blood can avoid accidents during blood drawing by following the above points. Finally, I hope everyone has a good body~