Blood tests

Find out how blood tests can help your doctor check for inflammation in the body and allergies and monitor your response to medicines. Blood tests can also show if other conditions could be causing your lung symptoms.

What are blood tests?

A blood test is a very common test. It’s a quick and simple test done in your GP surgery or local hospital.

Your doctor or other healthcare professional can explain if there’s anything you need to do to prepare for your test. For some blood tests, you may need to avoid eating anything for up to 12 hours before the test. You might be asked to stop taking certain medicines too.

How is a blood test done? 

When you have a blood test, a small amount of blood is taken, usually from a vein in your arm.

Your doctor or nurse or other healthcare professional may do the test. Often blood tests are done by a phlebotomist. A phlebotomist is a member of the healthcare team trained to take blood.

You may feel a slight scratch when the needle goes in, but blood tests are not usually painful.  Tell the person doing the test if you’re scared or anxious about tests using needles. They can reassure you or talk to you to distract you while the test is taking place.

The results from some blood tests come back quite quickly, but other types of blood tests may take longer. At your appointment, you can ask how long it will take to get the results from the blood tests you’re having.

The NHS has more information about what happens during a blood test.

Why do I need a blood test?

Blood tests are a really useful way to tell you and your GP more about your general state of health. They can show if you have an infection, and check how well body organs like your liver and kidneys are working.

Blood tests on their own are not used to diagnose your lung condition.

But alongside other types of tests, blood tests can help rule out anything else that could be causing your lung symptoms or making them worse. 

Different blood tests check for different things. Your doctor can choose the most useful test or tests for you to have.  

ACTH test

An ACTH blood test checks levels of ACTH in your blood. ACTH (Adrenocorticotropic hormone) controls the amount of cortisol in your blood.



Cortisol is a hormone made by the adrenal glands. It’s sometimes referred to as a ‘stress hormone’ because it helps the body respond to stress.

Cortisol helps keep your blood sugar levels normal. It’s also important for your blood pressure and your immune system. 

The ACTH blood test is useful when your doctor thinks you may have high or low cortisol, or thinks you may be at risk from adrenal suppression. This is when your adrenal glands stop producing your body’s own cortisol, which can happen if you have low levels of ACTH.

Low levels of ACTH can be a result of high doses of corticosteroids which are medicines you may need to take for your asthma or other lung condition.

Levels of ACTH in your blood can go up when cortisol levels are low and can go down when cortisol levels are high.

You will usually be invited for your ACTH blood test first thing in the morning. The test is usually done around 9am. This is when cortisol levels are highest.

Allergy test

If you’ve got any allergy signs or symptoms, your doctor may ask for an Immunoglobulin E (IgE) allergy test.

IgE is a protein in the blood. It helps protect our bodies from harmful substances. High levels of IgE protein in your blood can suggest that you’re allergic to something.

Your doctor may look for specific types of IgE, for example food allergens, if they think you could have a specific trigger that could be treated.

You may also have other blood tests like a full blood count. 

AATD test

Alpha-1 antitrypsin (AATD) is a rare genetic condition that can cause lung and liver disease.

An alpha-1 antitrypsin blood test may be used if your healthcare professional thinks you might be at risk of a genetic form of Chronic Obstructive Pulmonary Disease (COPD).

They might think you’re at risk because you developed COPD early, or you have a family history of COPD.

Find out more about alpha-1 antitrypsin deficiency. 

Blood gas test

A blood gas test is not like a normal blood test. This is because a blood gas test takes blood from an artery instead of a vein. It can show if your lung condition is affecting how much oxygen is getting into your body, and how much carbon dioxide is in your blood.

You may have this test in hospital if you have low oxygen levels for any reason. For example, you might not be getting enough oxygen in your blood if you have Chronic Obstructive Pulmonary Disease (COPD) or pneumonia.

If you’re prescribed oxygen, a blood gas test can show if oxygen therapy is helping you get enough oxygen to keep you well, but not too much to make you ill.

Read more about blood gas tests. 

Blood gas tests are usually done in hospital

This is so that the blood can be checked as soon as it’s been taken. Because a blood gas test takes blood from an artery instead of a vein, some people might find it more painful, and some may bleed more.

BNP test

A BNP blood test measures a protein known as BNP in the blood. BNP stands for B type natriuretic peptide.

A BNP blood test can help doctors understand what’s causing your breathlessness.

Higher than normal levels of BNP can show that your heart is not pumping blood as well as it could.

The blood test helps your doctors work out if your breathlessness is because of heart failure, a lung condition, or both.

Inflammation tests

CRP stands for C-reactive protein. A CRP test helps find inflammation.

Your doctor may request this test when they want to test for inflammation or infection in the body.

An ESR blood test is also used to help doctors check on levels of inflammation in your body. ESR stands for Erythrocyte Sedimentation Rate.

An EDR blood test is usually used with other blood tests because on its own it can only give general information about inflammation in the body. ESR levels can also be high because of infection.

An ESR test may be requested to check for inflammation as a result of sarcoidosis. Sarcoidosis is a lung condition where inflamed cells join up to make tiny lumps called granulomas. 

D-dimer test

A blood test called D-dimer tests for clots such as deep vein thrombosis (DVT) and pulmonary embolism (PE).

A pulmonary embolism is where pieces of a blood clot usually in the leg, break off and travel to the lungs. 

You may be given a D-dimer test to check if clots in your lung are causing your symptoms. Often this test is done to rule out clots as a cause for your symptoms.

The NHS has more information about pulmonary embolism

FBC test

A full blood count (FBC) is one of the most common types of blood test. It checks the cells in your blood, and it can give your doctor general information about your health.

A full blood count can show if:

  • your immune system is working well
  • other conditions, like anaemia could be causing your breathlessness
  • you may be fighting infections
  • your blood eosinophil count is high.

An eosinophil is a special type of white blood cell

High levels of eosinophils can show if your lung condition is related to allergies. If you have severe asthma, checking eosinophils in your blood can show if you’re more likely to respond to certain medicines.

Glucose tests

A glucose blood test can show if the levels of glucose (blood sugar) in your blood are high. Your doctor may ask for a blood test to check glucose levels if you’re taking certain drugs, including steroids. This is because high glucose levels can be a side effect of taking steroids.

High levels of glucose in your blood can be a sign of diabetes. Diabetes is a long-term condition that makes blood sugar too high. 

Some people with a lung condition who take long term steroids may be more at risk of diabetes.

Diabetes is sometimes checked with a blood test called an HbA1c test. Taking long-term steroids can be a risk factor for developing diabetes.

You may need to have a glucose blood test or an HbA1c test more than once to confirm a diagnosis of high glucose or diabetes. 

Skin prick tests

Cystic fibrosis is an inherited condition that causes sticky mucus to build up in the lungs.  

A skin prick blood test, also called a blood spot test, is used to test babies for cystic fibrosis.  

A skin prick test is not painful. It is not like a normal blood test. It uses a needle that only scratches the surface of the skin.

Most cases of cystic fibrosis can be picked up at birth with this test.

The blood will be sent to a lab where it is tested for a number of conditions, including cystic fibrosis. 

Theophylline test

Theophylline is a bronchodilator medicine which can help some people manage their asthma better.

If you’re taking theophylline, you’ll need regular blood tests to check the medicine is at safe levels in your blood.

A theophylline blood test checks for levels of theophylline in your blood.  

You may have one at the start of your treatment, and then at regular intervals. This is to make sure you’re continuing to take the drug at safe levels. Theophylline can be toxic at high levels.

U&E tests

U+E (Urea and Electrolytes) blood tests are groups of blood tests that show the health of your liver and how well your kidneys are working.

Tests like these can show if your body will deal well with certain types of severe asthma treatments and absorb them properly. 

Vitamin D test

Vitamin D is an important vitamin for healthy bones, teeth, and muscles, and for the immune system.

A Vitamin D blood test can show if you have low levels of vitamin D in your blood.

Your doctor may recommend this blood test if you’re on long-term steroids for your lung condition or if you tend to get infections, or if you spend a lot of time indoors.

If you have dark skin, or you cover up your skin, you may also be at risk of low vitamin D.

If your Vitamin D levels are low, your doctor may recommend taking a vitamin supplement.

Vitamin D - the 'sunshine' vitamin

During the summer months, most people can get all the vitamin D they need from the sunshine.

The NHS recommends that everyone in the UK takes a vitamin supplement during the winter months, October to March.

We have more information about vitamin D and your lung condition on our healthy eating page.

Read more about vitamin D on the NHS website.

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