Venipuncture, how to do it?

The withdrawal consists of acquiring a venous blood sample in order to investigate the patient’s state of health.

To avoid errors in execution, it is important to have it performed by competent personnel (doctor, nurse, biologist). The repetition of an incorrect withdrawal, besides being an economic waste (costs of non-quality) is a damage and an inconvenience for the patient.

For the correct execution of the withdrawal it is necessary to carry out the obligatory passages, in order to avoid problems in the laboratory investigations.

1) Inform the patient, who:

  • must not change their eating habits the day before the withdrawal.
  • must observe a fast of 8-12 hours before taking, abstaining from taking coffee, tea, milk or other drinks, except for natural water.
  • Must avoid intense physical exertion in the 12 hours prior to collection
  • must not smoke in the period between waking up and taking the sample
  • should not drink alcohol for 12 hours before taking it.
  • should not take any medication within 12 hours of collection except for mandatory prescriptions
  • must avoid excessive fasting, over 24 hours, due to the consequent decrease in blood sugar, cholesterol, triglycerides, thyroid hormones and increase in bilirubin, uric acid and creatinine.

2) Identify the patient always asking: surname, name and date of birth.

3) Label the samples:

Samples must be identified immediately prior to collection, with name and surname, date and place of birth, date of collection and department of origin, possibly using a barcoded identification system and making sure, in any case, that the identification number and code of the label correspond to those of the patient, through active identification. Where available, adopt the computerized acceptance system that provides automatic label printing, interfaced with the Transfusion Service. Further precautions are the not covering with the label of the filling notch on the test tube and the positioning of the label on the same in order to allow the visualization of the contents in order to evaluate the correct filling.

4) Prepare the material for collection:

The preparation of all the necessary material (or accessory) is an essential aspect for the implementation of a correct withdrawal, in order to optimize the procedure in terms of time and quality.

Essentially, the material should include:

– Disposable safety needles (preferably with caliber between 23 and 20 Gauge).

– Disposable Holder (or “shirt”)

– Fittings for coupling on butterfly or cannula needles

– Tubes for collection

– Skin disinfectant (preferably 70% alcohol solution, except for alcohol)

– Round gauzes or round cotton balls

– Patch

– Tourniquet

– Safety container for elimination of potentially infected material

5) Choice of withdrawal point:

The central veins of the cubital and cephalic forearm are preferable; alternatively, the basilic vein and those of the back of the arm can also be used. The veins of the wrist and hand are to be used only when the previous sites are not accessible, while those of the foot doses represent the last resort due to the greater probability of complications.

6) Place the tourniquet:

About 10 cm above the chosen site, use sufficient pressure to generate venous stasis but not to cause pain, discomfort or hinder the arterial circulation. The stay in the tourniquet for 1 to 3 minutes is the cause of hemo-concentration and therefore of alteration of some laboratory tests, due to the displacement (“shift”) of water and small analytes outside the vessel and consequent concentration of the molecules larger (eg hemoglobin and cholesterol among others)

7) Follow a specific order of tubes:

The vacuum tubes must be inserted in a specific order, which avoids the cross-contamination of additives (anticoagulants or coagulation activators), according to a well-defined order:

  • Coagulation test tubes containing sodium citrate (blue cap),
  • Serum tubes (red and / or orange cap),
  • Test tubes containing lithium-heparin (green cap),
  • Test tubes containing EDTA (purple cap),
  • Test tubes containing citrate and dextrose (yellow cap),
  • Test tubes containing oxalate and / or fluoride (gray cap)

8) Withdrawal techniques:

Lay the patient’s arm out so that it faces downwards. Make the puncture with the needle at an angle of 10-20 ° to the skin and in line with the chosen vein. Insert the needle 10-15 mm until it reaches the lumen of the vein: a sudden failure indicates the penetration of the needle into the vessel lumen. Use your free hand to insert the vacuum tube into the shirt, pushing it until the needle penetrates the rubber part of the cap. Loosen the tourniquet when blood is seen in the tube. Keep a gentle pressure on the bottom of the tube to keep it in place in the shirt. When the blood flow ceases and the first tube is full remove it gently from the holder and insert the other tubes in the shirt respecting the order of the tubes. The vein chosen must be found at the first attempt and, if this does not happen, avoid groped retrieval with repeated complete or even partial extractions of the needle (tissue trauma can be the cause of haemolysis and sampling pollution) and with a new needle take the sample on another vein.

9) Mixing of post-collection tube:

The correct mixing of blood and additives (anticoagulants or coagulation activators) is one of the most critical aspects in the collection procedure. In fact, the lack (or inefficient) mixing leads to an incomplete blood anticoagulation in the samples collected in tubes containing EDTA, sodium citrate or heparin (the major problems affect coagulation and blood counts), or incomplete coagulation activation in the samples collected in test tubes containing coagulation activators (with consequent risk of haemolysis, incorrect positioning of the separator gel or formation of microcoaguli or fibrin frustules that can interfere with some laboratory tests). It is therefore recommended to proceed with the systematic mixing of all the tubes immediately after collection, by gentle inversion of the same for 4-8 times (5 on average). It should also be remembered that excessive agitation (“shakeraggio”) can cause damage to blood cells (especially red blood cells, with in vitro hemolysis) or foam formation that prevents the correct positioning of the separator gel in the tubes that contain it.

10) Final disposal:

At the end of the procedure, it is necessary to eliminate all the material contaminated by the patient’s blood, transferring it to suitable safety containers. Under no circumstances should the needle used for collection be re-capped. The material used for disinfecting the skin (cotton) and any contaminated material must be thrown into the special waste container.