You or your child should not usually need any medical tests to diagnose chickenpox. You can be pretty sure that it is chickenpox if there are the key symptoms of a mild fever followed by an itchy rash, blisters and scabs. Chickenpox is a common viral illness that can have serious complications so seek help if unsure of the diagnosis.

Chickenpox spots are usually distinctive enough to distinguish from other rashes, although occasionally they can be easily confused with other conditions that affect the skin, such as insect bites or scabies (a contagious skin condition that causes intense itching).

If you're still uncertain about what is causing the symptoms, your doctor can carry out a simple blood test to identify the virus.

When to contact your doctor

See your doctor if you're not sure whether you or your child have chickenpox.

Contact your doctor urgently if you have been in contact with someone who has chickenpox or you have chickenpox symptoms and:

• you are pregnant
• you have a weakened immune system (the body's defence system)
• your baby is less than four weeks old.

Chickenpox in these instances can cause serious complications if left untreated. It is essential to seek medical advice so that you can receive any necessary treatment.

• Contact your doctor if you have chickenpox and are breastfeeding. They can advise about whether you should continue breastfeeding your baby.

Having a blood test

Once you have contacted your doctor, you may need a test to see if you're already immune from chickenpox.

If you have had chickenpox in the past, then it is extremely unlikely that you will develop chickenpox for a second time. If you've never had chickenpox, or you're unsure whether you've had it, then you may need an immunity test. This is a blood test that checks whether you are producing the antibodies to the chickenpox virus.

If your blood test result shows that you have the antibodies, you'll be naturally protected from the virus. If you don't have the antibodies, then you'll need to be monitored closely to see if you develop chickenpox symptoms. If you do, you may require further treatment.