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For most people, having blood taken is quick, easy and relatively painless.  Other people feel anxious and need some strategies to help them cope.  Children, the elderly, and people who have a disability may need special help when having a sample taken.

The blood needed for a diagnostic test is usually fairly easy to obtain. It requires a procedure called venipuncture (a term that quite simply means 'puncturing the vein'). The person performing this procedure may be your doctor, a nurse, or someone specially trained in collecting blood samples, a phlebotomist.

If you are feeling anxious or unwell or if you have previously fainted, let the person collecting the sample know. They will generally suggest you lie down. Also, let them know if you are allergic to medical tapes, isopropyl alcohol or latex.

What happens? 

The person collecting your blood sample will insert a small needle into one of your veins.  Usually this is in your arm. Usually, they are able to identify a vein that is easily accessible.  Clenching your fist, when you are asked to, helps make the vein more prominent. They will draw off a small amount of blood and it will run into tubes to send to the laboratory. After taking a sample of your blood, a cotton-wool dressing is taped over the puncture site. you will usually be asked to apply gentle pressure to help the blood clot and prevent swelling and bruising. Leave the dressing in place for a short time (usually 2–4 hours).

The tubes are sent to the laboratory where the blood is analysed according to the test your doctor has requested on the referral form.

If you faint or feel unwell during or after your blood test, you will be asked to stay until you have fully recovered.   If you have a tendency to bleed or bruise, let the collector know.  To help prevent bruising to your puncture site, do not carry anything heavy or undertake strenuous exercise within 24 hours of your blood test.

Will it hurt? 

When the needle is inserted under the skin you might feel a slight sting and there may be additional discomfort when it is withdrawn.

Not flowing well? 

Try drinking water and exercise. Drinking 8 to 10 glasses of liquid a day helps blood flow better and makes the veins more likely to stick up and be found easily, so drink plenty of fluids for a day or two before your test. But, also, remember to follow your doctor’s instructions - some tests require that you do not drink certain liquids prior to the test. You may also want to take a walk while waiting, or on your way to the test, to increase blood flow and keep the veins pumped up (routinely doing hand and arm exercises also helps those requiring frequent testing). Even eating well the day before, if fasting is not required, improves blood flow.

Cold hands? 

Being warm increases your blood circulation, which makes it easier for the phlebotomist to find a vein. If you have difficulty with blood being taken, lying down and warming your hands under a heating pad and blanket usually provide good results.

Difficulty with blood being taken? If you are among those people who have small or difficult-to-access veins, or veins that are scarred or blocked from repeated punctures (chemotherapy patients can have this problem) you may need to work with the person taking your blood to create a process that works well for you. 

What to do afterwards? 

If you experience swelling, bruising, or pain then follow putting ice on the site, using the affected arm as little as possible, and taking an over-the-counter painkiller can help.

Complications following a blood test

A blood test is an invasive procedure because a needle is inserted through the skin to reach a vein. It is however a very safe procedure. Millions of blood tests are performed in Australia every year. 

By far the most common complication is bruising at the site of the needle puncture. This usually appears within 24 hours and may range in size from a small spot to a large purple bruise. It is caused by blood leaking from the punctured vein out into the tissues just under the skin. This can be reduced by using finger pressure on the site for a minute or so after the blood has been taken.

Bruising is more likely if the collection is difficult, if pressure is not maintained on the site for a minute or so, if you are taking anti-clotting medicines such as aspirin or warfarin, if you are an elderly person with fragile veins, or if you exercise your arm soon after the blood test – such as by lifting heavy shopping bags or going to the gym.

While bruising is unsightly it is not dangerous and will slowly disappear over a few days or weeks, depending on how extensive it is. Large bruises may become tender for a few days because the cells that are involved in mopping up the bruise release substances that cause the area to become sore. This is uncommon but again not dangerous. It is part of the healing process. However, if the tenderness is bothering you, you should contact the person or clinic where you had the blood taken.

Very rarely, a small artery, which contains blood at much higher pressure than in veins, will lie unusually close to or underneath a vein. In this situation, the artery may be accidentally punctured. If this happens, you generally become aware of it within a few minutes because a painful deep swelling can be felt and sometimes seen. Tell the collector if this happens as it is necessary to apply firm pressure to the area for at least five minutes.  Almost inevitably you will develop extensive and sometimes spectacular bruising on the lower part of the arm over the next two to three days because the blood leaks to the underside of your arm with gravity. While this may appear dramatic it is not dangerous and will gradually disappear over a couple of weeks.

There are some rare complications but you have to be unlucky to suffer one of these. For example, you may have a tiny branch of one of the sensory nerves of the arm actually running over the surface of the vein. Rarely, the needle will hit this tiny nerve on the way into the vein. This may cause a short, sharp electric-shock type pain. This may be all that happens; however in some cases tingling type of pain may persist for one to four weeks, as the nerve heals. This is inconvenient and may be unpleasant but it eventually heals up.

Another rare complication is for a small clot (or thrombus) to form in the vein at the site where the needle was inserted. This is noticeable as a small firm lump just under the skin. The lump may or may not be tender and will go away over a couple of weeks.

Finally, there is the possibility of infection developing at the site of the needle puncture.  This is extremely rare and would be noticed as developing redness and pain. Most times, discolouration and tenderness around the needle puncture site are the result of bruises that are healing but if you are worried contact the person or clinic where you had the blood collection done or visit your doctor.
 

Other methods of collecting blood samples

Finger-pricks 
A small number of blood tests require just a finger-prick. A very small sample of blood from your capillaries can be obtained from the fingertip or earlobe, or from the heel or big toe of a newborn baby.

Warming the skin with moist, hot compresses for about 10 minutes helps blood flow to the area. The skin is then pricked with a lancet. Because there are more nerves in the finger than in your elbow, you may find that a finger-prick is a bit more painful than venipuncture even though it can seem less intimidating.
 
Arterial samples 
In more critical situations patients admitted into hospital may require blood to be taken from arteries. This procedure, known as an arterial sample, is performed by a doctor or specially trained nurse. A local anaesthetic may be administered and afterwards the nurse applies pressure to stop the bleeding and prevent bruising.