child fever blood test explained

Overview

A blood test is a common way to check for the cause of a fever in children. It looks for signs of infection, such as a bacterial or viral illness, by measuring things like white blood cells and C-reactive protein (CRP).

Blood tests are a routine part of care when a child has a high fever without an obvious cause, especially in young infants or if the fever lasts a long time.

Children of all ages, from newborns to teenagers, but it is more common in babies under 3 months old and in children with weakened immune systems.

Symptoms

Common symptoms

• High temperature (over 38°C or 100.4°F)
• Flushed or hot skin
• Sweating or shivering
• Feeling tired or irritable

Symptoms in children

• Fussiness or crying more than usual
• Poor feeding or loss of appetite
• Sleeping more or being hard to wake
• Clammy or pale skin

Causes

Main causes

• Bacterial infections such as ear infections, pneumonia, or urinary tract infections
• Viral infections like flu, colds, or chickenpox
• Other conditions such as autoimmune diseases or inflammatory disorders

Risk factors

• Young age, especially under 3 months
• Recent contact with someone who is sick
• Weakened immune system from illness or medication

When to see a doctor

See a doctor urgently if:

• Your child has a fever and any of the emergency symptoms listed above.
• Your baby is under 3 months old with a temperature over 38°C.
• Your child is very drowsy, confused, or not responding normally.

Book a routine appointment if:

• Fever lasts more than 3 days without improving.
• You are worried about your child's condition, even if the fever is low.
• Your child has a chronic illness like heart disease or sickle cell disease.

Diagnosis

The doctor will first examine your child and ask about symptoms. If they suspect a bacterial infection or need more information, they will recommend a blood test.

Tests that may be done

• Full blood count (FBC) to see levels of white cells, red cells, and platelets
• C-reactive protein (CRP) test to measure inflammation
• Blood culture to check for bacteria in the bloodstream

What to expect at your appointment

A nurse or phlebotomist will clean the skin and insert a small needle into a vein in your child's arm or hand. It may sting for a moment. They will collect a small amount of blood into a tube. Your child can have a bandage and a cuddle afterwards. Results usually take a few hours to a day.

Treatment

Treatment depends on what the blood test shows. If it finds a bacterial infection, antibiotics are often prescribed. For viral infections, the body usually fights it off with rest and fluids.

Self-care at home

• Give your child plenty of fluids like water or milk to prevent dehydration.
• Dress your child in lightweight clothes and keep the room comfortably cool.
• Let your child rest as needed, but do not force bed rest if they feel okay.
• Use fever-reducing medicine like paracetamol or ibuprofen only as directed by your doctor.

Medical treatments

If a bacterial infection is found, antibiotics (usually oral for mild infections or intravenous for severe ones) may be given. For some viral infections, antiviral medication might be used, but mostly the body heals on its own. Always follow your doctor's advice on which medicines to use and for how long.

When is surgery considered?

Surgery is not needed for fever itself, but rarely an infection like an abscess (collection of pus) may need to be drained.

Living with this condition

While waiting for test results or recovery, monitor your child's temperature and symptoms. Keep them comfortable at home. Most children can return to normal activities when they feel better.

Lifestyle tips

• Ensure your child gets enough sleep and rest.
• Encourage handwashing to stop germs from spreading.
• Avoid sending your child to school or daycare until the fever is gone and they are feeling well.

Diet and exercise

Offer light meals like soup or toast if they have an appetite, but do not force eating. Encourage drinking small amounts often. Gentle play or quiet activities are fine, but avoid running or sports until full recovery.

Mental health and emotional wellbeing

Having a fever and getting a blood test can be scary for a child and stressful for parents. Stay calm and reassure your child. Talk to them about what is happening in simple words. Most fevers and tests lead to good outcomes.

Prevention

Not all fevers can be prevented, but you can reduce the risk of infections that cause fever.

Vaccines

Routine childhood vaccinations (such as for measles, whooping cough, and pneumonia) protect against many illnesses that cause fever. Make sure your child's vaccinations are up to date.

Screening programmes

Screening is not typically done for fever, but if your child has repeated fevers, your doctor may recommend further tests.

Complications

If left untreated

• If a bacterial infection is not treated, it can spread and cause serious illness like sepsis.
• Very high fever can sometimes lead to dehydration or febrile seizures (convulsions) in young children, though these are usually not harmful long-term.

Long-term outlook

The vast majority of fevers in children get better on their own without lasting problems. With proper care and timely treatment when needed, children recover fully. A blood test can help give you peace of mind that the cause is identified.

Find support

Local organisations

• NHS 111 · United Kingdom

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