Blood tests · Guide
Understanding Blood Test Results
Blood test reports are full of abbreviations and reference ranges that can feel intimidating. This guide walks through the most common values — what they measure and what "high" or "low" usually means — so you can have a clearer conversation with your clinician.
Medipher explains medical wording in plain English — it does not diagnose or replace a clinician. If this is a medical emergency, call your local emergency number immediately.
Go deeper on a specific blood test
This page is the general introduction. Each guide below covers one panel in more detail.
What are blood tests?
A blood test is a laboratory measurement of the different cells, chemicals and proteins in a small sample of your blood. Individual tests are usually grouped into "panels" — for example a Full Blood Count (FBC) or Liver Function Tests (LFTs) — so a single sample can answer several clinical questions at once.
Why your doctor may request this test
Blood tests are one of the most common ways clinicians gather objective information. Being asked for one is usually routine — not a sign anything is wrong.
Why your doctor may request this test
- Investigating symptoms such as tiredness, dizziness or unexplained weight change
- Routine health checks or annual reviews
- Monitoring existing conditions like diabetes, thyroid or high blood pressure
- Checking how a medication is working or affecting the body
- Before or after surgery, as part of pre-operative assessment
- Investigating suspected infection or inflammation
- Pregnancy and antenatal monitoring
- Screening for common problems like anaemia or high cholesterol
Reference ranges
Every result on your report is compared against a reference range — the values considered typical for most healthy adults. Ranges vary slightly between labs, so always read the range printed on your own report rather than one you find online.
Clinicians look at the pattern across several results, your symptoms and your history — not a single number in isolation.
It also helps to keep two things apart. A result is a measurement of one substance in one sample at one moment. A diagnosis is a clinical judgement made by a healthcare professional using your results, your symptoms, your examination and your history together. A value outside a reference range can be associated with several different explanations, and on its own it does not confirm any of them.
Full Blood Count (FBC)
A Full Blood Count (FBC) — called a Complete Blood Count (CBC) in the US — is the most common blood test. It measures the three main cell types in your blood: red cells (oxygen), white cells (infection) and platelets (clotting).
The number of red blood cells, which carry oxygen around your body.
- If low
- Can suggest anaemia or blood loss.
- If high
- Can be linked to dehydration or, less commonly, lung or bone-marrow conditions.
Haemoglobin
Hb / HgbThe protein in red cells that actually carries oxygen. One of the most useful FBC values.
- If low
- A common sign of anaemia — you may feel tired, breathless or dizzy.
- If high
- Can be linked to dehydration, smoking or certain lung conditions.
Haematocrit
HCTThe percentage of your blood made up of red cells.
- If low
- Often moves with haemoglobin — can suggest anaemia.
- If high
- Often linked to dehydration.
The average size of your red blood cells.
- If low
- Small red cells can point to iron-deficiency anaemia.
- If high
- Larger red cells can point to B12 or folate deficiency, or heavy alcohol use.
MCH / MCHC
MCH / MCHCHow much haemoglobin is inside each red cell, on average.
- If low
- Often seen alongside iron-deficiency anaemia.
- If high
- Less common — usually interpreted with MCV.
The cells that fight infection.
- If low
- Can be caused by viral infections or some medications.
- If high
- Often a sign of infection, inflammation or stress on the body.
Platelets
PLTThe cells that help your blood clot.
- If low
- May increase bruising or bleeding.
- If high
- Can be reactive (e.g. after an infection) or need further investigation.
What this doesn't necessarily mean
- High white blood cells does NOT automatically mean a serious infection — stress, exercise, pregnancy and some medications can also raise them.
- Low haemoglobin does NOT always mean iron deficiency — B12, folate, pregnancy and long-standing illness can also cause it.
- A slightly out-of-range platelet count does NOT automatically mean a bleeding disorder — reactive changes after a recent infection are common.
- Small changes on one blood test rarely mean anything on their own — clinicians look at the pattern across several results.
Other common blood tests
These are short overviews. Each panel has its own detailed Medipher guide covering what every marker measures, how the results are read together and what may happen next. A laboratory result is a measurement, not a diagnosis — it is always interpreted alongside your symptoms, history and other results.
U&E (Urea & Electrolytes) and kidney function
- What it measures
- Kidney function and the balance of key salts such as sodium and potassium.
- Why it is requested
- Before or during medicines that affect the kidneys, to look into dehydration, or as part of routine health checks.
- What high values may suggest
- A higher urea or creatinine can be associated with reduced kidney function, but is also commonly seen with dehydration. Sodium and potassium outside the range are interpreted alongside your medicines and symptoms.
- What low values may suggest
- A lower sodium or potassium may be seen with some medicines, illness or hydration changes, and is interpreted alongside your symptoms.
What this doesn't necessarily mean
- A single raised creatinine does not by itself mean kidney disease — hydration and muscle mass can also affect it.
- Slightly out-of-range electrolytes are common and often settle on a repeat test.
LFT (Liver Function Tests)
- What it measures
- A group of values (ALT, AST, ALP, bilirubin, albumin) that reflect how the liver and bile system are working.
- Why it is requested
- To look into symptoms such as jaundice, tiredness or abdominal discomfort, or while taking certain medicines.
- What high values may suggest
- A raised ALT or AST can be associated with liver-cell irritation; a raised ALP or bilirubin may be seen with changes in bile flow. Mild rises are common and are interpreted alongside your history and other results.
- What low values may suggest
- A lower albumin can be seen in longer-standing illness and is reviewed alongside other results.
What this doesn't necessarily mean
- A mildly raised ALT does not by itself mean liver disease — recent exercise, alcohol or some medicines can cause temporary rises.
- A raised bilirubin does not always point to serious illness — Gilbert's syndrome is a harmless inherited variation that is common.
HbA1c
- What it measures
- Average blood sugar over the past two to three months.
- Why it is requested
- To screen for and to monitor diabetes and pre-diabetes.
- What high values may suggest
- A higher HbA1c can suggest that average blood sugar has been raised, and is interpreted alongside a repeat test and your overall picture.
- What low values may suggest
- Very low values are uncommon and may reflect conditions affecting red blood cells rather than blood sugar itself.
What this doesn't necessarily mean
- A single HbA1c in the pre-diabetes range does not mean diabetes is inevitable.
- A raised HbA1c does not automatically mean medication — a clinician considers your whole picture first.
TSH (Thyroid Stimulating Hormone)
- What it measures
- The main screening hormone used to look at thyroid activity.
- Why it is requested
- For symptoms such as tiredness, weight change, low mood or palpitations, or to monitor thyroid treatment.
- What high values may suggest
- A higher TSH can be associated with an underactive thyroid, and is usually read alongside free T4.
- What low values may suggest
- A lower TSH can be associated with an overactive thyroid, and often leads to further tests such as free T4.
What this doesn't necessarily mean
- A borderline TSH does not automatically mean thyroid treatment — mild changes often settle on a repeat test.
Cholesterol / Lipid profile
- What it measures
- Total cholesterol, LDL ('bad'), HDL ('good') and triglycerides.
- Why it is requested
- To help estimate long-term heart and stroke risk, or to monitor treatment.
- What high values may suggest
- A higher LDL or triglyceride level can be associated with greater cardiovascular risk over time, and is interpreted alongside blood pressure, age and other factors.
- What low values may suggest
- A lower HDL may be associated with greater cardiovascular risk; a low total cholesterol on its own is rarely a concern.
What this doesn't necessarily mean
- A high cholesterol result does not automatically mean medication — decisions weigh overall cardiovascular risk, not one number.
- One raised reading does not mean anything permanent — diet, illness and timing can all influence it.
When should I be concerned?
- Most abnormal blood tests are not emergencies.
- Many results are only slightly outside the normal range.
- Reference ranges differ between laboratories.
- Seek urgent medical advice if your report contains urgent wording, or a clinician has advised immediate assessment.
If this is a medical emergency, call your local emergency number immediately. Medipher is designed to help explain medical information and is not an emergency service.
Questions to ask your clinician
- Which of these results, if any, are you concerned about?
- Are any of my values outside the normal range, and by how much?
- Do any of these results need a repeat test — and when?
- Could any of my medications be affecting these results?
- Are there lifestyle changes that could improve these numbers?
Frequently Asked Questions
Should I worry about one abnormal blood result?
Usually not. Many results sit just outside the reference range without indicating a problem. Clinicians look at the pattern across several results, your symptoms and your history — not one number in isolation.
Why are reference ranges different?
Laboratories use slightly different equipment, methods and populations to define what is 'normal'. Always compare your value to the reference range printed on your own report, not one found online.
Can medicines affect blood tests?
Yes. Many common medications, including some antibiotics, blood pressure tablets and hormones, can influence liver, kidney or blood-count results. Always tell your clinician what you're taking.
Why has my doctor ordered repeat blood tests?
A repeat test helps distinguish a temporary change from an ongoing pattern. It doesn't automatically mean something is wrong — it's often just how clinicians confirm a result.
Can dehydration change blood test results?
Yes. Dehydration can raise haemoglobin, haematocrit, urea and some electrolyte values because the blood becomes more concentrated.
Can blood tests diagnose everything?
No. Blood tests are one piece of the picture. Many conditions need additional tests such as scans, biopsies or physical examination to diagnose.
Should I compare my results with someone else's?
It's rarely useful. Reference ranges vary by lab, age, sex and pregnancy, and a value that's fine for one person may be worth reviewing for another.
Can normal blood tests still mean something is wrong?
Yes. Normal results can be reassuring but do not rule out every condition. If your symptoms persist, tell your clinician even if your blood tests were normal.
Look up specific terms
Every value on your report has its own plain-English definition in the Medical Glossary.
Sources
Medipher guides are written from publicly available UK health information. They are educational and do not replace advice from your own healthcare professional.
- 01NHSBlood tests — Health A to Z
- 02Association for Laboratory MedicineLab Tests Online UK — Tests index
- 03National Institute for Health and Care Excellence (NICE)NICE guidance and advice list
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This guide is general health information, not medical advice. Reference ranges and clinical interpretation vary — always discuss your results with a GP, doctor, nurse or pharmacist.