Kawasaki disease - Diagnosing Kawasaki disease

There is no single test to diagnose Kawasaki disease. Your GP will confirm the condition by looking at your child's symptoms and carrying out a physical examination.

The National Institute for Health and Care Excellence (NICE) states that your child may have Kawasaki disease if they have a high temperature (fever) of 38C (100.4F) or above for longer than five days, and they have at least four of these key symptoms:

• conjunctival injection in both eyes: where the whites of your child’s eyes are red and swollen 
• changes to the mouth or throat: such as dry, cracked lips or a red, swollen tongue
• changes to the hands and feet: such as swollen or painful hands or feet, or red or peeling skin on the palms of the hands or soles of the feet
• a rash
• swollen lymph nodes in the neck

The skin on your child’s fingers or toes may become red or hard and their hands and feet may swell up. Your child's hands and feet may also be tender and painful to touch or to put weight on, so they may be reluctant to walk or crawl.

Read more about the symptoms of Kawasaki disease.

In some cases, Kawasaki disease may also be diagnosed even if a child does not have four or more of the key symptoms listed above. It may be that they have atypical (irregular) or incomplete Kawasaki disease.

If your child only had a fever for four days but they have four or more of the key symptoms, a diagnosis of Kawasaki disease may also still be made.

Further tests

Your child may need to have further tests to rule out other conditions that could be causing their symptoms. Possible conditions that your child could have include:

• scarlet fever: a bacterial infection that causes a distinctive pink-red rash
• toxic shock syndrome: a rare, life-threatening bacterial infection
• measles: a highly infectious viral illness that causes a fever and distinctive red-brown spots
• glandular fever: a viral infection that can cause a fever and swollen lymph glands
• Stevens-Johnson syndrome – a very severe allergic reaction to medication
• viral meningitis: an infection of the protective membranes (meninges) that surround the brain and spinal cord
• lupus – an autoimmune condition that can cause a range of symptoms including fatigue, joint pain and a rash

There are also several tests that can be carried out during the first 7-10 days to help support a diagnosis of Kawasaki disease.

Individually, these tests may not be conclusive but when combined with some of the key symptoms listed above, they can help to confirm a diagnosis. 

White blood cell count

A sample of your child’s blood will be tested to see how many infection-fighting white blood cells it contains.

In over 50% of cases of Kawasaki disease, the blood contains a higher number of white blood cells than normal. 

Platelet count

The number of platelets (clotting cells) in the blood may also be tested as part of the diagnosis.

The platelet count is usually at its highest during the second or third week of Kawasaki disease. A platelet count may not help diagnose Kawasaki disease during the first two weeks but it can be used to confirm a diagnosis later on.

Urine analysis

A urine sample may be tested to see whether it contains white blood cells, which could indicate Kawasaki disease. If your child has Kawasaki disease, their urine is unlikely to contain any bacteria. 

C-reactive protein

C-reactive protein (CRP) is produced by the liver at the start of an infection or inflammation in the body.

The amount of CRP in the blood can be measured. An increased level indicates inflammation or an infection.

A CRP test cannot identify the condition that is causing the inflammation but it can confirm whether there is a problem.

Erythrocyte sedimentation rate

The erythrocyte sedimentation rate (ESR) is a measure of how much inflammation there is in the body.

To calculate your child’s ESR, a blood sample will be placed in a test tube. The length of time it takes for the red blood cells to sink to the bottom of the tube will be recorded.

If the red blood cells sink faster than normal, it may mean that your child has an inflammatory condition, such as Kawasaki disease.

Like a CRP test, ESR can only indicate whether there is inflammation in the body but it cannot identify what is causing it.

Cerebrospinal fluid

Cerebrospinal fluid (CSF) is the protective fluid that surrounds the brain and spinal cord.

A procedure called a lumbar puncture is where a sample of CSF is taken by inserting a needle between the vertebrae (back bones) of the lower spine.

The fluid will then be tested for white blood cells which, if present, could also be a sign of Kawasaki disease.

Other blood tests

A sample of your child’s blood may also be tested to determine levels of:

• sodium (salt)
• proteins
• enzymes (proteins that speed up and control chemical reactions)
• lipid (fats)

If the blood sample contains abnormal amounts of any of these, it could be a sign of Kawasaki disease.

Read more information about blood tests.

Heart problems

Complications of Kawasaki disease usually affect the heart. Therefore, your child may need to have some tests to check that their heart is functioning normally. These might include an:

• electrocardiogram (ECG), which measures the heart's electrical activity using electrodes (flat metal discs) attached to the arms, legs and chest; an ECG can identify damage to the heart or problems with the heart's rhythm
• echocardiogram, which involves ultrasound (high-frequency sound waves) used to produce images of the heart which can confirm whether there are any problems with the heart’s structure or function

During the acute phase of Kawasaki disease (weeks 1-2), several heart abnormalities may be identified. These could include:

• tachycardia (a rapid heart rate)
• pericardial effusion (a collection of fluid in the heart)
• myocarditis (inflammation of the heart muscle)

In around 25% of cases of Kawasaki disease, the blood vessels around the heart (the coronary arteries) are widened slightly.

In most cases, these abnormalities will resolve six to eight weeks after the condition starts, although in some people further complications can develop.

Read more about the complications of Kawasaki disease.