Venipuncture:How To Take Blood?

Definition of venous blood collection

Venous blood collection is to collect blood samples for testing and analysis by inserting a thin tube into the human vein with a needle. Veins are a type of blood vessel in the human body with weak or even no pulse. They are usually located deep in the subcutaneous tissue and muscles, with thick walls, and are less affected by factors such as autonomic nerves and changes in body position, so they are suitable for blood collection. When collecting blood, medical staff will perform multiple steps such as disinfection, puncture, and fixation to ensure the safety and accuracy of blood collection. Venous blood collection is a common medical operation and is widely used in clinical medicine and scientific research.

Common uses of venous blood collection

1. Disease diagnosis

Venous blood collection is an important means of diagnosing a variety of diseases. By analyzing the various components in the blood, doctors can identify and judge the condition.

Routine blood tests: used to check red blood cells, white blood cells, platelets, etc. in the blood to help diagnose anemia, infection, leukemia and other diseases.

Infection diagnosis: By detecting pathogens or inflammatory markers (such as C-reactive protein, leukocytosis, etc.) in the blood, it is determined whether there is bacterial or viral infection.

Liver function and kidney function tests: By testing liver enzymes (such as ALT, AST), creatinine and urea nitrogen, the functional status of the liver and kidneys is evaluated.

Blood sugar and diabetes testing: Venous blood sugar testing can help diagnose and monitor blood sugar levels in diabetic patients.

2. Physical examination and prevention

Venous blood sampling is a routine item in health examinations and is used to detect potential health problems early.

Full body examination: In routine physical examinations, venous blood sampling is used to check blood lipids, blood sugar, blood routine, liver and kidney function, etc. to assess overall health status.

Preventive testing: For groups with a family history or higher risk, regular blood sampling can detect signs of cardiovascular disease, diabetes or cancer early.

3. Treatment monitoring

Venous blood sampling is used to monitor the patient's physical response and drug effects during treatment.

Drug concentration monitoring: For antibiotics, immunosuppressants, anti-epileptic drugs, etc., blood sampling is used to detect the concentration of drugs in the blood to ensure that the drug dosage is appropriate.

Tumor marker detection: Monitor the treatment effect and disease progression of cancer patients by detecting specific tumor markers (such as AFP, CEA, CA-125, etc.).

Diabetes monitoring: Diabetic patients adjust drug treatment and diet through regular blood sugar monitoring.

4. Blood transfusion matching and blood type detection

Blood type detection: The patient's ABO blood type and Rh blood type can be detected through venous blood sampling to help match the appropriate blood type for transfusion.

Cross-matching: To prevent incompatible blood transfusions, doctors perform cross-matching tests on blood donors and recipients through blood sampling to ensure safety.

5. Hormone level detection

Venous blood sampling can be used to detect various hormone levels in the body to diagnose endocrine diseases or evaluate the effectiveness of hormone-related treatments.

Thyroid function test: Such as testing thyroid hormone (T3, T4, TSH) levels to help determine hyperthyroidism or hypothyroidism.

Reproductive hormone detection: used to detect testosterone, estrogen, progesterone, etc., to diagnose male or female endocrine disorders.

Adrenal and pancreatic hormone testing: such as testing insulin, cortisol, etc., to help determine conditions such as diabetes or Cushing's syndrome.

6. Cardiovascular disease risk assessment

Venous blood sampling can be used to assess the patient's risk of cardiovascular disease.

Blood lipid testing: By testing total cholesterol, low-density lipoprotein (LDL), high-density lipoprotein (HDL), triglycerides, etc., the risk of atherosclerosis and coronary heart disease is assessed.

C-reactive protein (CRP) testing: CRP is an inflammatory marker, and high levels of CRP in the blood are often associated with a high risk of cardiovascular disease.

7. Coagulation function assessment

By testing the coagulation function of the blood through venous blood sampling, doctors can understand whether the patient has bleeding or coagulation abnormalities.

Coagulation factor testing: such as prothrombin time (PT), partial thromboplastin time (APTT), etc., to assess whether the coagulation mechanism is normal.

Thrombosis risk assessment: such as D-dimer testing, used to assess the risk of thrombosis, especially in patients after surgery or suspected deep vein thrombosis.

8. Diagnosis of metabolic disorders

Electrolyte testing: Electrolyte levels such as sodium, potassium, calcium, and magnesium are tested in the blood to diagnose electrolyte disorders, especially in patients with kidney disease or dehydration.

Acid-base balance testing: Testing bicarbonate, carbon dioxide, pH, etc. in the blood to determine acid-base imbalance.

9. Immune function assessment

Immune function testing is performed through venous blood sampling to evaluate the status of antibodies, immune cells, and complement systems in the body.

Diagnosis of autoimmune diseases: such as rheumatoid arthritis and systemic lupus erythematosus, which are diagnosed by testing autoantibodies (such as ANA, RF, etc.).

Immune response to infection: Testing IgG and IgM antibody levels to evaluate the body's immune response to viral or bacterial infections.

Common sites for venous blood sampling

1. The first choice is the antecubital vein of the arm, with the priority being the median vein, cephalic vein, and basilic vein.

2. When it is not possible to draw blood from the antecubital vein, the superficial vein on the back of the hand can also be selected.

3. When special patients with severe systemic edema, extensive burns, etc. cannot find a suitable puncture vein in the limbs, blood can be collected from the superficial vein of the neck or the femoral vein.

Operation steps of venous blood collection

1. Before blood collection, medical staff need to wash their hands and wear gloves to ensure aseptic operation. Prepare blood collection tools, including vacuum blood collection tubes, syringes, tourniquets, sterile cotton, gauze, etc.

2. Let the patient sit or lie comfortably and relax his arms. Usually, the blood collection site is selected in the vein of the elbow or the back of the hand.

3. Use a tourniquet to gently tighten the patient's upper arm to enhance the visibility and touch of the vein. At this time, the medical staff determines the location of the vein by touch and gently presses the vein with their fingers.

4. Disinfect the blood collection site with alcohol cotton balls or disinfectant to avoid infection. When disinfecting, it is usually done by drawing circles from the center to the outside to ensure thorough cleaning.

5. Keep the bevel of the needle facing up and insert the needle into the vein quickly and steadily. Pay attention to the angle and strength when inserting the needle to avoid repeated punctures that cause pain to the patient.

6. Blood begins to flow into the blood collection tube, and medical staff collect different amounts of blood samples as needed. Be careful not to collect too much to avoid discomfort to the patient.

7. After the collection is completed, loosen the tourniquet and quickly pull out the needle, while pressing the blood collection site to prevent bleeding.

8. Each blood collection tube should be clearly marked with patient information and sent to the laboratory for analysis as soon as possible.

Precautions for venous blood collection

After the blood collection is completed, immediately press the puncture site with a sterilized dry cotton swab. Press longitudinally for 3-5 minutes at the needle eye and 1 to 2 cm above to stop bleeding. Do not rub to prevent subcutaneous hematoma. Keep the puncture arm clean and dry within 24 hours. The pressing time after blood collection should be sufficient. Due to individual differences, each person's coagulation function is different. Patients with poor coagulation function need to press for a longer time. Therefore, if the skin surface does not seem to bleed, stop pressing immediately, which may cause incomplete hemostasis, and blood seep into the subcutaneous area to cause siltation.

If there is a tendency to bleed, the pressing time should be extended. If local siltation has occurred, a hot towel can be applied after 24 hours to promote the absorption of siltation. After blood collection, the patient should rest for 15 to 30 minutes, sitting or lying down to rest. If symptoms of needle phobia or hypoglycemia occur, the patient should lie flat on the spot immediately, drink some sugary drinks, and leave after the symptoms are relieved.

Common problems and solutions for venous blood collection

1. Loosening time of the compression band

After 1 minute of tourniquet compression, the hematocrit and hemoglobin levels begin to increase, and there are obvious changes after 2 minutes, and the degree of increase is related to the compression time of the tourniquet. If the time is too long, it can also cause hemolysis. Therefore, the tourniquet should be loosened when the first tube of blood is collected, and the use time should not exceed 1 minute.

If in some cases the tourniquet needs to be used in one part for more than 1 minute, it is advisable to loosen the tourniquet and wait for 2 minutes before re-tying it.

2. Treatment when blood collection is difficult

The correct treatment for patients with blood collection difficulties is to pre-heat the blood collection point or ask the patient to clench his fist repeatedly, because the above measures can promote blood circulation, fill the local veins, and make puncture easier.

If you use the method of patting the arm or pushing the blood collection point, it will cause changes in blood flow, blood flow velocity, plasma composition and blood vessel wall pressure, which is easy to cause congestion and venous dilation, thus affecting the test results of certain indicators.

3. Poor blood flow

Before blood collection, check whether the vacuum tube has cracks and whether the tube cover is loose, etc., to prevent the failure of blood collection due to the lack of negative pressure in the tube.

Choose thick, straight and elastic blood vessels, and the first choice is the vein in the antecubital area of the arm. The priority order is the median vein, the cephalic vein and the basilic vein. When it is impossible to draw blood in the vein in the antecubital area, you can also choose the superficial vein on the back of the hand. See and feel the direction of the vein clearly, and choose the location and angle for needle insertion.

During the blood collection process, the angle of the blood collection needle can be adjusted, and the patient is instructed to alternately clench and loosen his fist. If it is still ineffective, the puncture needs to be repeated and the punctured vacuum tube needs to be replaced.

4. Blood leakage

When collecting multiple tubes, the silicone tube of the blood collection needle should be folded back before each replacement of the vacuum tube to prevent the needle latex sheath from being damaged due to repeated punctures, and the needle is exposed and leaking blood; the needle is prohibited from piercing from the side of the sheath, which will cause the sheath to be unable to recover and leak blood.

5. Blood sample mixing method

Turn the blood collection tube upside down 180° and mix it once. When collecting whole blood samples, attention should be paid to anticoagulation. After blood collection, the test tube should be gently rotated immediately to fully mix the blood and anticoagulant to prevent blood coagulation.

When collecting serum samples, do not shake them vigorously to avoid red blood cell rupture and hemolysis.

6. After blood collection, remove the needle first and then press

If the method of pressing first and then removing the needle is adopted, the needle is easy to produce friction with the blood vessel wall due to the application of cotton swabs to press above the puncture point, and the needle will have a cutting effect on the blood vessel wall, which will increase the pain.

Therefore, after blood collection, the needle should be removed first and then pressed, so that the blood collection needle can withdraw from the blood vessel without any pressure, the force is more uniform, and it is more convenient to press, which can significantly reduce pain and reduce congestion.

Summary

Venous blood collection is an important part of clinical diagnosis. Although the operation is relatively common, each step needs to be strictly implemented to ensure the accuracy of the blood sample and the safety of the patient. During the blood collection process, medical staff must not only have good technical skills, but also maintain good communication with patients to provide high-quality medical services.

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