What causes slow blood flow in blood draw?

In cases where blood is donated or blood is needed for testing, the process of blood drawing is required. Some people will find that the blood flow is slow during the blood drawing. This may be caused by thin blood vessels, the person being drawn is nervous causing blood vessel contraction, or the blood is too viscous, etc. This requires people to understand the reasons before they can adjust them. The following is a detailed introduction to the reasons for slow blood flow during blood drawing.

1. The thickness of the blood donor's blood vessels. The thicker the blood vessels, the more blood will flow out per unit area and the blood will flow faster. Conversely, the blood will flow slower.

2. The emotions of blood donors. When blood is being drawn, if the blood donor is extremely nervous, it will cause vasoconstriction, venous collapse, and slow blood flow, especially for first-time blood donors. Because it is their first time to donate blood, the psychological pressure will be relatively high. At this time, the blood donors themselves need to adjust their mood, such as talking and chatting with the blood collection staff, reading newspapers and magazines, etc. to relax themselves and relieve psychological pressure.

3. Blood viscosity. When the blood viscosity of a blood donor is relatively high, the speed of blood donation will be slower. At this time, you can drink some water to reduce blood viscosity and increase blood flow rate. In daily life, you should pay attention to eating a light diet, drinking plenty of water, and increasing exercise to alleviate the phenomenon of blood viscosity.

Notes on blood draw:

1. Fast after 8pm

You should fast after 8 pm the night before blood drawing: avoid drinking excessive amounts of alcohol, as the alcohol content in the blood will directly cause the results to increase or decrease; before having blood drawn to check blood lipids, it is best not to eat foods that are too high in fat, such as shabu-shabu, braised pork, etc.; before checking cholesterol, eat less eggs, as these will affect the composition of the blood and cause "misjudgment."

2. Do not do strenuous exercise in the morning

You should get enough sleep the night before blood collection and avoid strenuous exercise in the morning. Because strenuous exercise can temporarily increase the levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), etc., and can also cause changes in blood components such as potassium, sodium, and blood sugar, affecting the measurement results.

3. Fatigue will affect the results

Before having your blood drawn, you should avoid being overly tired or exposed to extreme cold or heat stimulation, as this may cause an increase in your white blood cell count.

4. Don’t wear thick clothes

On the day of blood collection, do not wear clothes with sleeves that are too tight or too small. Otherwise, the sleeves will be too tight and you will not be able to roll up your sleeves when blood is drawn, or it will be difficult to stop the bleeding, causing hematoma in your arm. At present, everyone is wearing a lot of clothes, so it is best to take off your outer clothes and thick sweaters before drawing blood.