Bruising after a blood test: what is normal and when to get it checked

The NHS says you may get some bruising or swelling around the area where your blood was taken and that this should go away after a few days. Ashford and St Peter's Hospitals calls bruising or haematoma the most common complication of the blood test procedure and says it should subside after a few days.

The Wensum Valley practice, which publishes patient guidance for its own blood tests, adds that you may get a bruise or a small lump, which will usually settle by itself and fade away in time. It notes that bruising can look very dramatic and some people may find this worrying, particularly if it appears away from the site where the blood was taken or is visible for a few days. It is usually harmless and will go away in time.

In plain terms, a bruise is a small amount of blood that has leaked into the tissue around the vein. Most people notice no more than a tender spot.

Northern Care Alliance explains that a large area of bruising is usually due to insufficient pressure being applied once the needle has been removed, or to damage to the vein when the needle was inserted because of fragile veins. It says that although this can be painful it usually resolves within a few days, and that patients taking anticoagulants will bruise more easily.

The Wensum Valley practice lists several factors that increase risk: drugs such as warfarin or aspirin, conditions such as a bleeding disorder or low platelets (thrombocytopenia), difficulty getting a vein, for example if the arm is swollen with oedema, and older patients. East Sussex Healthcare gives anticoagulants such as warfarin, rivaroxaban and aspirin as examples of medicines that slow the blood's ability to clot.

Technique also matters. East Sussex lists the steps staff are trained to take: avoiding pushing the needle too deep, releasing the tourniquet once blood flow is achieved and applying pressure after the needle is removed. It adds that nerves are very small and nearly impossible to find, which is why occasional pain can occur even with good technique.

The measures are simple and consistent across the leaflets. Press firmly on the site until bleeding has stopped. Keep your arm straight while pressure is applied. Northern Care Alliance asks you to keep the arm straight throughout the procedure and immediately afterwards and to keep the dressing on for at least one hour. East Sussex says the dressing can be removed after 20 minutes if you wish.

Avoid heavy lifting for a short while. Wensum Valley suggests keeping the arm slightly raised and avoiding too much movement, such as lifting or carrying heavy parcels, for an hour or so, and East Sussex suggests not carrying heavy bags or leaning on the arm for at least 5 minutes. Ashford and St Peter's says that resting, elevating and applying ice to the site can help reduce bruising.

If you notice bruising or prolonged bleeding after you leave, Wensum Valley advises applying further firm pressure to the area, and says a few ice cubes wrapped in a towel may help reduce swelling and bruising.

• Press firmly on the site until bleeding stops, with your arm straight.

• Keep the dressing on for the time the clinic advises.

• Avoid lifting or carrying heavy items with that arm for a short while.

• Ice wrapped in a towel may ease swelling.

• Tell staff before the test if you take blood thinners or bruise easily.

Most bruises need nothing. Northern Care Alliance says that if the area becomes red or swollen you should seek advice from your GP, and that you should tell staff immediately if you feel intense pain or burning during the procedure. It also says that tendon or nerve damage is a rare complication of venepuncture, and that medical advice may be required because it can take weeks to resolve.

East Sussex Healthcare lists possible complications and what to do. For infection it advises keeping the area clean and dry after the appointment. For nerve damage it says pain can last from a few days to a few months, and to inform staff of previous occurrences. For pain, it says you can request that blood is taken from your non-dominant side next time.

Wensum Valley adds that some people continue to feel discomfort or pain at the site, probably because of nerves under the surface of the skin, which should settle quite quickly, and that if it does not you should see your GP or a member of hospital staff. Prolonged bleeding should be met with further firm pressure. Pain that persists, a change in feeling in the arm or hand, or a bruise that keeps spreading is worth raising with your GP or the clinic that took the sample.

A bruise at a blood test site is expected. Bruising that appears without a needle or a knock is a different question and has its own guidance, which the related pages below cover.

If you know you bruise easily or take blood thinners, mention it before the test so the person can press for longer afterwards. Wensum Valley asks you to tell the person taking blood if you have any such conditions or have had a problem in the past after a blood test.