In short. Blood tests before surgery do two different jobs. A full blood count, kidney and liver function and sometimes a clotting screen establish whether your body is fit to be operated on, while a group and screen or a full cross-match make sure the right blood is matched and ready if a transfusion is needed. Most people never need blood.
Key points
- Blood tests before surgery check fitness for the operation and prepare blood in case it is needed.
- A group and screen is enough where transfusion is unlikely; a cross-match is done when bleeding is expected.
- Autologous donation suits only some patients and has drawbacks, including a lower starting count.
- Being asked for a cross-match does not mean your team expects a problem.
- Anaemia found early can be corrected before the day of surgery.
What the two kinds of test are for
Blood tests before surgery do two different jobs. Some establish whether your body is in a fit state to be operated on. Others make sure that, if you need blood during or after the operation, the right blood is ready and waiting. Keeping those two purposes apart makes the list easier to read: the first group is about you, the second about what may be needed on the day.
The tests most patients have
A full blood count shows whether you are anaemic, whether your white cells and platelets are normal, and gives a baseline against which any change after surgery can be measured. Tests of kidney and liver function show how your body clears drugs and anaesthetic agents. A clotting screen may be added if you take medicines that affect bleeding, or if you have a history of bleeding problems.
How blood is matched and held ready
Your blood group and your antibodies are recorded in advance. A group and screen is enough for operations where transfusion is unlikely; a full cross-match is done when bleeding is expected, or when you have antibodies that make matching more complicated. Cross-matching is what allows blood to be issued quickly and safely if it is needed, and it takes time, which is one reason these tests are done before the day.
| Test | What it establishes | When it is used | What it allows |
|---|---|---|---|
| Full blood count | Anaemia, white cells, platelets and a baseline | Routinely before surgery | Early correction, and a comparison after surgery |
| Kidney and liver function | How your body clears drugs and anaesthetic agents | Routinely before surgery | Knowledge of how you clear them before the day |
| Clotting screen | Whether bleeding is a problem | If medicines affect bleeding or there is a history | A known problem rather than a surprise |
| Group and screen | Your blood group and antibodies | Where transfusion is unlikely | Blood to be issued if it is needed |
| Full cross-match | A matched unit held ready | Where bleeding is expected or matching is complicated | Quick, safe issue without delay |
| Autologous donation | Your own blood, given beforehand | Only when time, count and likely need allow | Your own blood, at the cost of a lower starting count |
Should you donate your own blood before the operation?
Autologous donation means giving blood for your own use before a planned operation. It is offered only in certain situations, because it is not suitable for everyone: you need enough time before surgery, a good enough blood count, and an operation where transfusion is genuinely likely. It also has drawbacks, including a lower blood count going into surgery and the fact that donated blood still has a shelf life. Whether it is worth doing is a decision to make with your team.
What happens if you are anaemic beforehand?
Anaemia is common and often treatable. Finding it early gives time to correct it, which is far better than discovering it on the morning of surgery. This is one reason blood tests are done in advance rather than treated as a formality.
What should you tell the team before the day?
Tell your team about previous transfusions or reactions, about any antibodies you have been told about, about blood disorders or a history of clots, and about medicines that affect bleeding. If your religion or your personal beliefs mean you would decline blood products, say so at the assessment and not on the day: the team can plan alternatives, but only if they know in advance.
The details worth raising early are any previous transfusion reaction, or antibodies you have been told about after pregnancy or after a transfusion; any personal or religious position on receiving blood products; and bleeding problems, easy bruising, a family history of bleeding, or any medicine or supplement that affects clotting.
Planning is a precaution, not a prediction
Transfusion planning is a precaution, not a prediction. Most people having most operations never need blood. The tests exist so that if it is needed, the right unit is matched, available and safe to give without delay. Being asked to have a cross-match does not mean your team expects a problem.
Sources
- World Health Organization: patient safety information on safe surgery and blood
- National Institute for Health and Care Excellence: perioperative care guidance
- Royal College of Anaesthetists: patient information on preparing for surgery and anaesthesia
Internal links
Frequently asked questions
What is the difference between a group and screen and a cross-match?
A group and screen records your blood group and antibodies and is enough where transfusion is unlikely. A full cross-match is done when bleeding is expected or matching is complicated, and it allows blood to be issued quickly and safely.
What does autologous donation mean?
Giving blood for your own use before a planned operation. It suits only certain patients, because you need enough time before surgery, a good enough blood count and an operation where transfusion is genuinely likely. It has drawbacks, including a lower starting count.
What if I would decline blood products?
Say so at the assessment, not on the day. The team can plan alternatives, but only if it knows in advance. Tell them about previous transfusions or reactions, antibodies you have been told about, and any bleeding disorder.
Risks & Limitations
- Preparing well lowers the risk of an operation, but it cannot remove it. Every anaesthetic and every operation carries risk that preparation reduces rather than eliminates.
- The instructions that apply to you are the ones given by your own surgical and anaesthetic team. General guidance, including everything on this site, cannot know your operation, your history or your other medicines.
- Stopping or changing a prescription medicine without advice can be dangerous — particularly blood thinners, diabetes treatment and steroids. Never do so on the basis of something you have read.
- An operation may still be postponed or cancelled on the day, even when you have prepared carefully. Illness, uncontrolled blood pressure or blood sugar, a fasting breach, or a theatre or equipment problem can all require it.
When to Seek Care
- Tell the hospital before your operation if you develop a fever, a productive cough, vomiting or diarrhoea, a wound or skin infection, chest pain, or any change in your usual medication.
- If you become acutely unwell — severe breathlessness, chest pain, confusion, fainting or a rapid worsening of any symptom — seek emergency care rather than travelling in for surgery.
- After discharge, contact the number your team gave you if you develop a fever, spreading redness or swelling around the wound, worsening pain, or a wound that is separating or discharging.
- If you are unsure whether something is urgent, treat it as urgent and ask. It is always acceptable to call.
References & Further Reading
- World Health Organization (WHO) — surgical safety and patient safety resources
- National Institute for Health and Care Excellence (NICE, UK) — perioperative care guidance
- Royal College of Anaesthetists (UK) — public information on anaesthesia and preparing for surgery
- Chongqing West District Hospital — your own pre-operative assessment and written instructions
This page is patient education, not medical advice, and it does not cite individual studies. Your own surgical and anaesthetic team gives you individual instructions, and those instructions take precedence over anything written here. To arrange a pre-operative assessment at Chongqing West District Hospital, see Contact & Consultation.