What Is a Full Blood Count (FBC) Test, and What Does It Show?

What is a full blood count test?

A full blood count, or FBC, is a blood test that counts and measures the three types of cell floating in your blood: red cells, white cells and platelets.

Your blood sample is usually taken in a 4ML tube-which comes back with somewhere between 14 and 20 separate numbers on it.

You might also see it called a complete blood count or CBC.

What is tested in a full blood count?

A full blood count usually tests for these:

Full blood count test normal ranges in the UK

What we described below are the typical adult ranges from an NHS pathology lab as well as the one that we see in our lab.

Your own report may differ slightly, because every lab sets its own reference ranges and the machines are calibrated differently.

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If your result comes back with a number outside this range, it does not automatically mean that it’s a problem. Your result is unique for your case and is best discussed with your GP.

What does a full blood count test show?

A full blood count test cannot usually diagnose something, but rather it is used to flag conditions such as:

• Anaemia – low haemoglobin, with the MCV hinting at whether iron, B12 or folate is behind it.
• Infection – a raised white cell count, with the differential suggesting bacterial or viral.
• Inflammation – persistent changes across white cells and platelets.
• Bleeding and clotting problems – a low or very high platelet count.
• Bone marrow disorders – including leukaemias, which usually announce themselves through abnormal white cell counts.
• How you’re tolerating treatment – which is why anyone on chemotherapy, methotrexate or certain immunosuppressants has regular FBCs.

It’s also the standard test before surgery, during pregnancy, and in any workup where somebody says “let’s start with bloods”.

What is not included in a full blood count test?

As the name suggests, this test only provides a full survey of your blood count and the cells associated with it.

It does not test for:

• Cholesterol. That needs a lipid profile.
• Diabetes or blood sugar. That needs a fasting glucose or HbA1c.
• Iron levels. An FBC can suggest iron deficiency through low haemoglobin and a small MCV, and measuring your actual iron stores needs a separate ferritin test.
• B12 and folate. A large MCV can hint at a deficiency, and confirming it takes its own test.
• Liver function. That’s an LFT panel.
• Kidney function. That’s U&Es.
• Thyroid, testosterone, oestrogen or any other hormone. All separate.
• CRP or ESR. These are inflammation markers ordered alongside an FBC, and they’re not part of it.
• Calcium, vitamin D or other minerals. Separate again.
• HIV, hepatitis or any other specific infection. An FBC might show your immune system reacting to something. But to check for HIV, hepatitis, or any other specific infection, you would have to go for a sexual health screening test.
• Pregnancy. That’s hCG.

If you want most of the above covered in a single appointment, that’s what our wider health packages are for. You can book one through our services list, or contact us in case of any questions.

Does a full blood count test show cancer?

Sometimes, and that really depends on the type of cancer.

Blood cancers such as leukaemia usually do change the FBC, often drastically, as they can show up as an abnormal white cell count.

Solid tumours are a different story. Bowel, lung, breast, prostate and most other cancers can leave an FBC looking completely normal.

Where they do show up, it’s usually indirectly, through an unexplained iron deficiency anaemia caused by slow internal bleeding.

So a normal full blood count is more of a routine test, and it cannot be used as a cancer screening test.

If you have symptoms that worry you, an FBC is a sensible first step for doctors to get more data on your bloods- and not the last one.

Do you need to fast before a full blood count?

No. You can eat and drink normally before an FBC, and no special preparation is needed.

But only when your full blood count test is bundled alongside a cholesterol or glucose test, the fasting instruction may be given.

We also recommend drinking water beforehand. This is because well-hydrated veins make it easier for us to retrieve the blood sample.

How long does a full blood count take?

The blood draw itself takes a couple of minutes. You’ll be in and out of the clinic in well under half an hour.

You can also expect to get the results faster than most blood tests. This is because the sample runs through an automated analyser and does not require any growing or culturing, unlike urine samples.

When you book a private full blood count test, most routine panels come back within 1 to 2 working days.

How to book a private full blood count test in London

The usual reasons people pay for a private full blood count test in London is the lack of a waiting list as well as convenience.

When you go private, you get to pick the day, no GP referral needed, and you also get results in one or two days.

At our London Private Ultrasound, we’d recommend going with the Complete Health Check Blood Test at £359 as it covers haematology and biochemistry, including the full blood count and ESR.

If you’d rather start smaller or go broader, the full range of blood test packages runs from £219 upwards.

Here’s why our patients book with us:

If your results need following up, we’ll provide a referral letter, and we can arrange a follow-up consultation with one of our doctors at an additional cost.

Frequently Asked Questions