How does chemotherapy affect the blood?

Chemotherapy can affect the blood cells. This can cause side effects, such as an infection.

Chemotherapy can affect the blood cells. Blood cells are made in the bone marrow, which is in the middle of your bones. Chemotherapy can damage the bone marrow, which reduces the number of blood cells. This can cause side effects.

There are three main types of blood cells.

  • White blood cells fight infection. The most common type of white blood cell is called a neutrophil.
  • Red blood cells carry oxygen around the body. The part of the cell that carries the oxygen is called haemoglobin.
  • Platelets are tiny cells that help the blood to clot.

You will have regular blood tests, called a full blood count, to check your blood cell levels. If the number of blood cells drops, the main side effects are:

If you have these side effects your chemotherapy may be delayed while they are treated, or while your blood cell levels recover. The blood cell levels should return to normal after your treatment, or if you have a longer break between treatment cycles. Your oncologist (cancer doctor) may lower the dose of your chemotherapy in your next cycle, which can help stop these side effects from happening again.

Your chemotherapy team should give you an emergency number to call if you are unwell,

or if you need information about any side effects. Your nurse will explain how to use this number, and when you should call them. If you haven’t been given a number, ask your nurse about this.


A low level of white blood cells may mean that your body is less able to fight an infection. An infection is an emergency if you are having chemotherapy. It can be life threatening and needs treating straight away, as it won’t get better without medical help. Don’t ignore the signs of an infection.

Signs of an infection include:

  • a high temperature
  • feeling shivery and cold
  • headaches and sore muscles
  • a cough or sore throat
  • pain or burning when you pass urine
  • feeling generally unwell or tired.

What do I do if I have a high temperature?

A high temperature is 37.5°C or 38°C, depending on the advice of your chemotherapy team. It is a sign of infection. Call the emergency number if you have signs of an infection.

If you can’t get hold of the chemotherapy team, go to A&E and tell them you are having chemotherapy. You should also phone if you suddenly feel unwell and have flu-like symptoms, even if your temperature is normal or low. A low temperature is 35°C and below.

Everyone having chemotherapy should have their own digital thermometer to check their temperature.

‘‘We were given a ‘chemo card’, so if we went to A&E he could be prioritised.’’

How is an infection treated?

Antibiotics can be used to treat an infection. Your chemotherapy may be delayed until your infection has been treated.

Your oncologist may give you an injection called G-CSF (granulocyte-colony stimulating factor) during your chemotherapy. This can help prevent infection as it helps your body make more white blood cells. It isn’t used with all chemotherapy drugs, so speak to your oncologist about whether you will have it.

It may be a good idea to get the flu vaccination before or during your chemotherapy. Speak to your chemotherapy team about this. You should also avoid any dental treatment once you start chemotherapy, as this can increase your risk of getting an infection. If you do need urgent dental care, speak to your oncologist first.

If you are having gemcitabine, you may get some flu-like symptoms such as feeling hot, cold or shivery. These symptoms normally happen while you are being given gemcitabine, or up to 24 hours later. These symptoms are a side effect of gemcitabine, not an infection. You should call your chemotherapy team if they don’t get better after a day.

Can I take paracetamol or ibuprofen while having chemotherapy?

Paracetamol and ibuprofen can be used to help manage pain. But they can also lower your temperature. This can hide the signs of an infection and make you feel better – but it won’t cure the infection.

Always check your temperature before taking these painkillers. If your temperature is high, call your chemotherapy team on the emergency number straight away before you take any paracetamol or ibuprofen.


Some chemotherapy drugs can lower the number of red blood cells in the blood. This is called anaemia. It can make you feel tired, weak, faint and short of breath.

If your red blood cell level is very low, you may need to be given blood through a drip. This is called a blood transfusion, and will increase your red blood cell levels. Macmillan Cancer Support have more information about blood transfusions.

Bleeding and bruising

Chemotherapy can lower the number of platelets in your blood – this is called thrombocytopenia. Platelets are cells that help blood to clot. If the number of platelets drops, you may be more likely to have nosebleeds, bleeding gums or tiny red spots on your skin. You may also bruise more easily than normal. If you have a nosebleed that doesn’t stop after five minutes, call your chemotherapy team who will be able to help.

You may need a longer break between your chemotherapy cycles to allow your platelet level to recover. Or your oncologist may change the dose of the chemotherapy drug.

Updated August 2019

Review date August 2021

This information is currently under review