Why Do I Need a Repeat Blood Test?

Written by
The Manual Team
Medically approved by
Dr Earim Chaudry
Last updated
24th March 2021

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In 30 seconds

Why do I need a repeat blood test? That’s usually because your doctor, nurse, or pharmacist struggled to accurately interpret your test results. This is quite normal and can happen for a variety of reasons. So, it’s not an immediate cause for concern.

It might be that your results are borderline, i.e. on the threshold of two different readings. Or it could be that your results are completely anomalous, suggesting that there may have been something wrong with the test. There’s also the possibility that more tests are needed to get a full picture of your health.

Regardless, you must take a repeat test if requested. It will help your doctor better understand – and treat –  any health problems you may have.

Understanding Blood Tests

Blood samples are some of the most important tools that doctors have to help you understand your health. Used to gain an insight into everything from your cholesterol and glucose levels to the health of your thyroid, blood pressure, and kidney function, they are incredibly useful. As a result, if you’re having a health check-up, you shouldn’t be surprised if you’re required to take a blood test.

But what about a retest? Why would you need a repeat blood test? When the stakes are high, it can be disconcerting if something unexpected occurs. However, repeat blood tests are normal – and there are many possible reasons why they might be necessary.

To reassure you, here we take a look at some of the reasons why you might need to redo a blood test. 

Why Would I Need a Blood Test?

Before any retest, though, you’ll need to take a test in the first place. 

Your blood is very helpful for doctors – and for you – to get an insight into your overall health. It carries all of the important nutrients, minerals, and proteins around your body. And it’s particularly helpful as it can be extracted and analysed pretty easily.

So, why might you need a blood test? Here are some of the reasons why a blood test might be useful. Trust us, though, that there are many, many more.

  • To monitor your overall health. General tests including the full blood count (FBC) and the electrolyte test check the balance of the contents of your blood.
  • To check your cholesterol levels. Cholesterol is a fatty substance that accumulates in your blood. Tests can tell you just how much of it you have and whether it is a problem for your health.
  • To see how quickly blood coagulates. Slow blood clotting can be fatal. A test can show you how quickly yours coagulates.
  • To keep an eye on blood sugar levels. Tests like the HbA1c blood test monitor your blood glucose levels over time. This can be life-saving for people with diabetes.
  • To identify signs of cancers. Some tests look for the symptoms of cancer in your bloodstream.

Why Do I Need a Repeat Blood Test?

Just as there are plenty of reasons why you might need a blood test in the first place, there are many reasons why you might be asked to have a repeat test.

Here are some of the most common. In all cases, the simple fact is that your doctor will want to be sure that the reading is correct. That’s their job – and they wouldn’t be doing a good job if they weren’t sure.

1. Some tests require more than one sample

To start with the obvious, some tests require more than one sample of blood. The HbA1c test, for example, should ideally be taken every 3 to 6 months. If you are newly diagnosed as diabetic, that may come as a surprise, but it is crucial to do it regularly to monitor your blood sugar levels.

Similarly, some blood tests are used to monitor other chemicals in your blood too. In these cases, one test will rarely be enough.

2. Abnormality, or unexpected results

If a doctor has been monitoring your health over time, they might request a retest if they see something out of the ordinary. This could be an entirely different value to what they usually find, or else a result they were not expecting.

If it is just a random anomaly (which does happen!), then a retest will confirm that. But if it is a potential sign of something more serious, your doctor needs to be sure.

3. ‘Borderline’ results

A common reason for retests is that your results are at one end of the normal range. For doctors to be sure that they are diagnosing you correctly – or that they are providing you with the right advice or medication – then they may request a retest just to be sure.

This doesn’t necessarily mean that your results are anything to worry about, however. Your doctor will tell you in due course if there is evidence of a health condition that needs to be monitored or treated.

4. Mistakes or errors

Even in the best healthcare systems in the world, mistakes and errors are possible. Leaking or broken samples, while uncommon, for example, do happen – and these mean that your sample will be contaminated and unusable. In this case, it’s understandable that you will need to do another test.

5. False positives

During the coronavirus pandemic, a lot of attention has turned to testing for infection. As you may have read during this time, tests – and that includes blood tests – are not always 100% accurate. When tests deliver a wrong result, these are called false positives. They don’t happen often, but it is more likely with some tests than others. 

It may be that your test has returned results that your doctors believe to be wrong. In which case, they will order a repeat to double-check.

What to Do If You’ve Been Asked to Take a Retest

If you are told that you will need to retake a blood test, the procedure will be the same as the original test. However, there are some things that you should do your best to bear in mind:

  • Don’t panic. We know that things can be a little disconcerting when they are unexpected. However, there is no reason for you to worry if you are asked to take a retest or further tests.
  • Follow your healthcare provider’s instructions. As with any test, you should do exactly what your GP or nurse tells you when taking a test. That means if you need to fast, do it properly (as that may be the reason for your abnormal results). If your doctor tells you not to eat before a blood test, it’s important that you don’t.
  • Ask any questions you may have. The best way to find out why you need a retest is to ask the healthcare professional with whom you are having your tests. They will be happy to explain the reasons to you – and will be able to put you at ease.

If you have taken a test through Manual, our medical team will give you all the information you need on the reasons behind your retest. Whether it’s through online messaging or a phone consultation, we’ll clear up any doubts you have. 

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Key Takeaways

Why do I need a repeat blood test? The answer is simple: your doctor wants to be sure about your results. 

What’s important to bear in mind, though, is that this doesn’t necessarily mean bad news. Rather, from damaged samples to surprising results, there are lots of different reasons why you might need a retest. Ultimately, your doctor should explain to you the reason.

References

  1. BBC News – Coronavirus testing: What is a false positive?: https://www.bbc.com/news/54270373

While we've ensured that everything you read on the Health Centre is medically reviewed and approved, information presented here is not intended to be a substitute for professional medical advice, diagnosis, or treatment. It should never be relied upon for specific medical advice. If you have any questions or concerns, please talk to your doctor.

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