INR tests at home for warfarin

The International Normalised Ratio (INR) test measures how long it takes for the blood to clot. This information from Great Ormond Street Hospital (GOSH) explains about carrying out INR tests, reporting results and what to do next.

INR tests are a vital part of treatment with anti-coagulants such as warfarin. Some families may be able to do these INR tests at home, so avoiding regular trips to Great Ormond Street Hospital (GOSH) or their local hospital. It should be read in conjunction with the information booklet provided by CoaguChek®, which is the machine used by GOSH. 

What is an INR test and why is it important?

INR test results are used to make sure that the dose of warfarin is giving the right amount of anticoagulation. Having too much warfarin can cause bleeding as the blood becomes too thin and having too little means that the blood will remain too sticky and at risk of clotting. Your child will be given a ‘target INR range’ by the staff looking after your child. 

This target INR varies from child to child depending on his or her condition. Your child’s target INR will be written in his or her warfarin record booklet. Ideally the INR should be within the range given and every time your child has an INR, the dose could be increased, decreased or remain the same depending on the result. Each time, your anticoagulation contact will make sure you understand how much warfarin to give your child.

Can everyone do INR tests at home?

No, it is not suitable for everyone. At GOSH, we will only recommend doing INR tests at home if your child:

  • has an agreed training plan between your family and the nursing team
  • you have completed a training package
  • has attended all scheduled INR tests and clinic visits

If your child fits in to this category, please talk to us about the possibility of doing INR tests at home.

Once we have agreed that you and your child can do the tests at home, we need to liase with the doctors and nursing team in your local area to confirm that they support home INR testing. If this is the case, we will then need to talk to your family doctor (GP) to confirm prescription of the supplies needed for the CoaguChek® machine, testing strips and warfarin medication.

Learning about the CoaguChek® machine

Before you go home with the CoaguChek® machine, we will teach you how to use it safely. You will need to watch a DVD about the machine and read the written information produced by the manufacturer. You will be given the DVD and information to keep. The main things we will teach you are listed below.

  • Preparation of the equipment
  • Quality assurance of results
  • Safety
  • Carrying out a test
  • Understanding the results
  • Contacting the team for dosing changes

We will also ask you to confirm that you have learnt these skills by signing a record form in your teaching information pack. A copy of this form will be sent to all healthcare professionals involved in your child’s care. Remember that we will make sure that you are confident in doing your child’s INR tests before you go home.

How do I do an INR test with the CoaguChek®?

Full information about doing an INR test is included with the CoaguChek® device but the main points follow. Remember that with some children, it is easier to get a blood sample from their foot rather than fingers. We will show you the best way for your child.

1. Make sure you have all the equipment you need ready

  • CoaguChek® machine
  • Test strip
  • Results booklet and pen

2. Wipe the area clean and wash your hands
3. Ask your child to wash his or her hands in warm water and dry them
4. Ask your child to shake his or her arms and wriggle his or her fingers (or toes if this is where you will take the sample)
5. Insert a test strip into the meter, which will switch on automatically
6. Confirm strip code and wait for the strip to warm up
7. Prick your child’s finger (or toe) with the lancet and put a drop of blood on the test strip
The meter will tell you if you have put enough blood on the test strip
The meter will tell you if the INR test has been done correctly and give you the result in a couple of minutes
If your child’s target INR has been programmed into the machine and the result is outside this range, the meter will tell you
The meter stores up to 100 results automatically
Record the result in your yellow warfarin booklet

Remember that once you have pricked your child’s finger, you only have 15 seconds to put the blood sample on the test strip before it starts to clot. If you run out of time or the machine tells you that the sample is not big enough, you will need to start again with a new test strip and pricking another of your child’s fingers.

Parents have told us that using distraction techniques and rewarding testing can help children cope with the finger pricks. Patients on warfarin will be invited for a six-monthly review coinciding with clinic attendance and general review. Patients with reduced oxygen saturation may require assessment three-monthly.

What do I do with the results?

We will advise you how often to do an INR test as this varies from child to child. If you are doing routine testing once a week, try to do the test during office hours so that you can discuss the result with your anticoagulation contact. When you have done a test, you should ring your anticoagulation contact with the test result. They will then check whether your child’s warfarin dose is correct. If you do need to change the dose, they will check that you understand how to take the new dose of warfarin.

Quality Control

Please bring your CoaguChek® machine to any appointments/admissions to carry out a test as usual. Sometimes an extra sample of the blood for testing in the laboratories may be needed. This extra sample can be taken from the same finger but needs to be done within a few seconds of the CoaguChek® sample.

Storing your CoaguChek® machine

  • The machine is sensitive to heat and moisture, so store it in a warm, dry place away from direct sunlight.
  • Everything you need to carry out INR tests at home is included in the storage bag so do not put it in another container.
  • Keep the machine and equipment out of reach of children.

Cleaning your CoaguChek® machine

  • Put your used lancets and test strips in a sharps bin. Your family doctor (GP) or community team or anticoagulation contact should provide this for you and arrange disposal when full.
  • After use, wipe the CoaguChek® machine over with a clean cloth, dampened with warm water and a little washing-up liquid, before drying with another clean cloth
  • If blood gets inside the test strip guide, you will need to remove this part carefully for cleaning. This will be demonstrated during training and the instructions are given in the CoaguChek® user manual provided with the machine 

How do I order new supplies?

Once you have the CoaguChek® meter, you should be able to get all the supplies needed on prescription from your family doctor (GP). An order form is included in your information pack. If you have any difficulty getting supplies on prescription, please tell us.

Compiled by: 
The Haematology, Cardiology and Neurology departments in collaboration with the Child and Family Information Group
Last review date: 
January 2015


Please note this is a generic GOSH information sheet. If you have specific questions about how this relates to your child, please ask your doctor. Please note this information may not necessarily reflect treatment at other hospitals.