How deep should blood be drawn for disease screening?

The needle for venous blood collection (puking the elbow vein, etc.) usually has a needle insertion of 2~5mm, and the peripheral blood collection (pricking the fingertip, heel, etc.) usually has a needle insertion of 1.5~2mm. The specific depth will be flexibly adjusted according to the blood collection object, blood collection site, and blood vessel conditions.

In fact, many people struggle with this issue. Most of them are afraid of staring at the needle in the nurse's hand when drawing blood, fearing that the other person's hand will prick too deeply and hurt themselves. When I was helping at a community free clinic, I met an uncle who was growing a greenhouse. The calluses on his fingertips were as thick as polished kraft paper. He used the normal setting to pierce 2mm, and only a little blood seeped out for a long time. ”

If you often go to the blood collection window and squat for a while, you will find that the depth of peripheral blood collection is actually the most controllable. Nowadays, disposable peripheral blood collection needles basically have fixed settings. For adults, use the 2mm setting for routine blood collection and rapid blood glucose collection. For children and newborns, use the 1~1.5mm setting for heel blood collection. Unless the callus is particularly thick and the skin is particularly rough, it will basically not exceed the reference range and will not damage deep tissues.

Compared with the pain of pricking a finger, more people are afraid of having to draw blood from a vein in the arm, because the depth of this thing fluctuates a lot. In the past, the young nurses in the department and the old head nurse who had worked for 20 to 30 years specifically talked about this matter. The young nurses are now learning comfort care. When they meet healthy young people with blood vessels as bulging as small earthworms, the needles are inserted quickly and shallowly, 2mm is enough. The patients basically feel no pain and the experience is particularly good. ； However, the old head nurse prefers to "insert deeper and deeper", especially for the elderly with loose skin and fragile blood vessels, or patients who need to draw five or six tubes of blood for a full set of screenings. The needle should be inserted to 4~5mm, and the needle is firmly fixed and will not easily roll out or leak blood. Instead, there is no need to suffer the sin of a second puncture. There is nothing wrong with both statements, but the applicable scenarios are different.

I also met a young man who weighed nearly 200 pounds. The blood vessels were buried under the fat. It took him a long time to feel the outline. The needle was inserted almost 6mm before blood was drawn. The young man was prepared for pain, but he was stunned for two seconds and asked, "Is it inserted?" ” In fact, it is not true that the deeper the needle is inserted, the more painful it is. The pain is more related to the sharpness of the needle and the speed of needle insertion. Some nurses insert the needle so fast that you have already withdrawn it before you can react. Even if the needle is inserted 4mm, you will not feel anything. If the needle is inserted slowly to the nerve endings on the surface of the skin, even if it is only inserted 1mm, it will make you wince in pain.

Speaking of which, many people are worried about whether the nerves will be injured if the needle is inserted too deep. You can rest assured about this. Nurses with formal training will avoid the location of the nerves. Even if the blood vessels are particularly deep, the depth of the needle will not exceed 1cm. It is basically impossible to damage the deep nerves and tissues.

If you really want to avoid suffering, rub your hands and shake your arms before collecting blood to let the blood vessels fill up a little. If you know that your blood vessels are deep and difficult to find, just tell the nurse in advance, and they will naturally adjust the angle and depth of the needle. To put it bluntly, there is no standard answer for how deep to insert blood. The core goal is to collect enough blood in one shot and cause as little trouble to you as possible. Rather than tying a few millimeters of blood, it is more practical to pay attention to pressing the needle hole after collecting blood and not rubbing it.