Ask the Doc: 'I've been told I need a blood test, what will that show?'
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Dr Laura Ryan answers your health questions.
Q. My GP has recommended a blood test, what are the use of these?
A. Blood tests have a wide range of uses and are one of the most common types of medical test. For example, a blood test can be used to:
- assess your general state of health
- check if you have an infection
- see how well certain organs, such as the liver and kidneys, are working
- screen for certain genetic conditions
Most blood tests only take a few minutes to complete and are carried out at your GP surgery or local hospital by a doctor, nurse or phlebotomist (a specialist in taking blood samples).
A blood test usually involves taking a blood sample from a blood vessel in your arm.
The arm is a convenient part of the body to use because it can be easily uncovered. The usual place for a sample to be taken from is the inside of the elbow or wrist, where the veins are relatively close to the surface.
Blood samples from children are often taken from the back of the hand. Their skin may be numbed with a special spray or cream before the sample is taken. A tight band (tourniquet) is usually put around your upper arm. This squeezes the arm, temporarily slowing down the flow of blood and causing the vein to swell. This makes it easier for a sample to be taken.
Before taking the sample, the doctor or nurse may clean the area of skin with an antiseptic wipe.
A needle attached to a syringe or special container is inserted into the vein. The syringe is used to draw out a sample of your blood. You may feel a slight pricking or scratching sensation as the needle goes in, but it shouldn't be painful. If you don't like needles and blood, tell the person taking the sample so they can make you more comfortable.
When the sample has been taken, the needle will be removed. Pressure is applied to the skin for a few minutes using a cotton-wool pad. A plaster may be put on the small wound to keep it clean.
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